Suspension Optimization and Tuning Help

[AutoX_a_Truck?]

After seeing several of Ron’s very educational threads I decided that it was time to put in some extra work and go to the next level and try to optimize my less than ideal budget setup. Here is a basic breakdown of my vehicle.

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1972 International Scout II
T: 2,805 lbs (F: 1,460 lbs & R: 1,345 lbs)
F: 52%
R: 48%
(These are close estimates based on less than ideal four corner scales, which were downhill and showed 53% & 47%. I am in the process of getting more accurate up-to-date weights)
Wheelbase: 99.75”
FT: 57.8375”
RT: 57.25”
Ride Height Behind Front Tire: 4”
Ride Height Center of Crossmember: 4.25”
Estimated CG Height: 12” (That's the height to the center of the harmonic balancer, but I am not sure that is entirely accurate for my vehicle)
Front Tires: 315/35/17 Nitto NT05 on 17x11” (11.5” tread width)
Rear Tires: 335/35/17 Michelin Pilot Sport 2 on 17x12.5” (12.5” tread width)

Front Suspension:

The front suspension is S10 based with a combination of aftermarket and stock style parts. It’s a basic stock style 2” drop spindle, with a larger stock style 33mm sway bar from a newer model and RideTech PosiLinks.

The tubular upper control arms are from a swap meet and apparently were designed for a metric dirt car, but have been modified. The upper arms use Allstar Adjustable ball joints adjusted approximately 1” from the tallest setting.

The lower control arms are RideTech StrongArms with the standard Moog ball joint.

The upper spring pocket has been removed to fit a 4.1” stroke RideTech Triple Adjustable Coilover with 4.1” stroke (10.125” compressed & 14.225” extended) running a 10” tall 2.5” ID 450 lbs/in spring.

I believe that my front suspension might possibly be considered a “Tweener” set up or at least it might be possible to set it up as a Tweener. Taking actual shock travel measurements at an event or by simulating event conditions is a priority once the weather is better. But for now I can only estimate based on videos and jouncing the front end that my front shocks can compress about 2.5-2.75” under heavy braking and are nearly bottomed out when the front cross member scrapes.

I typically shoot for about -1 degree of static camber, 0 toe in/out, and according to the FasTrax Adjustable Caster Camber Gauge I can currently register about 8.5-8.6 degrees of caster.

I am also battling a relatively high scrub radius due to my 17x11” wheels with just 4.25” backspacing. Using the method in Lance’s thread, I measured the scrub radius at 4 13/32”

A few videos for reference:

http://www.youtube.com/watch?v=R9o9UwR99fE&feature=share&list=PL4SXSAXaWtpC7_3_ZYHurp7H6zsMZlgX7

http://www.youtube.com/watch?v=ISMsvaYOpuE

An older video with the ‘47 truck body, but same basic setup with similar front weight. In this video the fender drag quite a bit because I had a tall passenger riding shotgun.

http://www.youtube.com/watch?v=t3Jg_RBur7Q

Here’s a really tight GG course where I struggled with tons of push in the middle of the corner.

http://youtu.be/2RlgucBBqO4?t=1m8s

Steering:

The S10 spindle steering arm geometry has always annoyed me because it’s front steer and the arm is actually angled forward toward the centerline of the front of the frame because the tie rod must clear a tire (for small diameter stock style wheels) or in my case the wheel itself. Moving the tie rod end outward any further will require shortening the steering arm at least an inch or two so that it can clear the rim lip and barrel, but I have not quite been able to determine whether this is feasible or not. I have a 12.7:1 Grand Cherokee steering box. The stock spindle steering arm has a flat base at the end where the tie rod end mounts, but there was room for moving the mount back slightly, which effectively shortened the arm with good results.

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Rear Suspension:

Homemade truck arms with a single front pivot point (spherical bearing). The truck arms are mounted solid to the axle pad underneath the axle tube with RideTech Triple Adjustable Coilovers mounted behind the axle. It has an adjustable pahhard bar.

After reading the mapping instructions, and then rereading them again, my dad and I spent the better part of two days developing creative ways to map out the front suspension. There were small, but mostly consistent variations side-to-side, but we double checked each measurement and/or checked against a different measuring method in some cases. I have those measurements in a spreadsheet. Thus, if possible, I would like to set and tune the front roll center height.

I primarily want to excel at autoX and tighter corners. I drive to events, but comfort is largely not an issue as long as the setup is not so harsh on wear parts that a 200 mile trip is out of the question. I also occasionally run track days, where I think the Scout feels much easier to drive than on a tight autoX course, but I do these mostly just for fun. At Mid-America Motorplex I was not running 10/10ths by any means as it was only my 2nd time on course, I have very little formal training, and I do not have anything near a racecar level of safety gear. Anyway, once I was a bit braver at the end of the day my quickest timed and recorded lap with Harry’s Lap Timer was 1:47. One of the quickest times I logged without a video was nearly a 1:46 flat with a gear limited top speed of 128 mph on the main straight. I am told that a good driver with a stock C6 Z06 should run in the realm of 1:45.

I favor running a modern high travel/low roll setup if possible, but I think I would currently fall into a tweener setup.

As I was reading through some of the helpful threads I came up with a few general goals based on what I have read so far:

1) Map the roll center and correct problems shifting towards a high travel/low roll setup if feasible
2) Correct and potentially improve LCA geometry
3) Correct and potentially improve UCA geometry
4) Build in Ackerman steering (I think but am not certain that my steering geometry is a huge hinderance on tight autoX courses)
5) Dial in caster and caster gain
6) Determine if more sway bar is necessary
7) Determine if spring rate changes are necessary
8) Possibly revalve my Ridetech coilovers if appropriate
9) Properly dial in and adjust my coilovers
10) Learn as much as possible

[Ron Sutton]

Sounds like a plan Tyler.

Can you convert your excel spreadsheet into a JPG file & post it up? If you have Photoshop or Adobe Pro, those will do it. Otherwise, you'll need to post them up manually.

Also, I'd like to see more photos showing all angles of your rear suspension & steering. Post some of bottom view, side view & front or rear view.

A few questions for you to answer ...
1. Is that an aftermarket spindle? It looks kind of like a CPP.
2. Does each truck arm have its own pivot or do the two arms join at the front forming a triangle like old Model A suspensions?
3. Get a height measurement to the front pivot(s) of the truck arms.
4. Get a height measurement to the mating surface of the truck arms & the housing brackets.
5. Did you measure motion ratios of the springs? If not, please do.
6. List the spring rates front & rear.
7. Have you calculated effective rates on the sway bars? if not, I'll show you how, but I need photos showing me the shapes.

[bmbrzmn101]

This should be a good learning experience for us all.

Looking forward to reading it.

Chris

[SSLance]

Subscribed...

I've seen this truck\car\SUV Scout thing run in person and it is impressive. I'm certain with Ron's tutulage and Tyler's fabrication skillz and driving it'll only get faster.

[AutoX_a_Truck?]

Sounds like a plan Tyler.

Can you convert your excel spreadsheet into a JPG file & post it up? If you have Photoshop or Adobe Pro, those will do it. Otherwise, you'll need to post them up manually.

I see the spreadsheet JPG did not work the first time so I had to reattach it as a PDF.

90202 UPDATED on 2/14/2014 because there was a round off error for the Passenger Lower arm rear pivot.

Also, I'd like to see more photos showing all angles of your rear suspension & steering. Post some of bottom view, side view & front or rear view.

Here are some pictures I have on hand of the steering and rear suspension. For the rear suspension, obviously it was easier to use a few older pictures from earlier in the build. I can try to get some better views if necessary.

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Ignore the wide spacer on the front end. That was just a mockup for a narrower set of front wheels that I used on the street with the truck body.

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For the steering, I also included an older picture of center link and tie rod setup too because it was slightly better.

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A few questions for you to answer ...

1. Is that an aftermarket spindle? It looks kind of like a CPP.

Yes, the spindles are generic aftermarket drop spindles, but I do not know what brand they are. I bought them used. If the brand is important I might be able to find some identifying marks, but I did not see anything obvious such as part numbers or markings.

2. Does each truck arm have its own pivot or do the two arms join at the front forming a triangle like old Model A suspensions?

The two arms join at the front forming a triangle. It is 48” from the center of the pivot point to the center of the axle.

3. Get a height measurement to the front pivot(s) of the truck arms.

5 3/8”

4. Get a height measurement to the mating surface of the truck arms & the housing brackets.

10 1/2”

5. Did you measure motion ratios of the springs? If not, please do.

I quickly searched through a few of the threads here and at Lateral-g, but I did not find a definitive gold standard method for measuring the motion ratio in the front suspension thread. In the past, I have used the simple method of distance from LCA pivot center to shock mount divided by LCA pivot to center of ball joint. Currently, works out to 0.578 (8.5/14.7), but I am open to suggestions on gathering a better measurement.

6. List the spring rates front & rear.

Front: 450 lbs/in
Rear: 150 lbs/in

7. Have you calculated effective rates on the sway bars? if not, I'll show you how, but I need photos showing me the shapes.

In the past I have tried a few methods I have seen online to get a rough estimate, but I do not have accurate numbers. Here are some pictures of the sway bars. The front is what the larger (33mm on the bottom) looks like compared to the original in the top picture. The bottom picture shows the rear sway bar, which is 32" long with 8 5/8" arms that have some adjustment.

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[Ron Sutton]

A few quick questions before I get started ...

1. Is there a bushing or monoball in the front pivot point of the rear suspension triangle where it connects to the frame?
2. With no bind or even pressure ... how far will the rear end housing articulate (angle difference to the frame) each direction ?
3. Front sway bar: What diameter? Solid? If hollow, what wall thickness?
4. Rear sway bar: What diameter? Solid? If hollow, what wall thickness?

[UMI Tech]

Anything Ron works with gets faster. Or better. Or whatever the goal is.

Subscribed.

[AutoX_a_Truck?]

A few quick questions before I get started ...

1. Is there a bushing or monoball in the front pivot point of the rear suspension triangle where it connects to the frame?

It is a ¾” spherical bearing pressed in a tube. There is probably a possibility of bind at extreme articulation, but I have not seen any evidence of that during testing or inspection.

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2. With no bind or even pressure ... how far will the rear end housing articulate (angle difference to the frame) each direction ?

When we designed the rear end and installed the RideTech Coilovers it was possible to hold either end of the axle against the frame (max compression travel) with the opposite end at full shock extension (with no springs installed) without bind. I do not think this amount of articulation would ever occur in the real world except maybe to a much smaller extent when driving one wheel at a time into a steep gas station entrance. If exact angles are needed I can do some tests to measures those, but that will probably have to wait until the weekend.

The only time I have seen a similar setup in use was on an Agent 47 Mustang prototype. It appears to have a more sophisticated front pivot, but the picture is too small to tell exactly what it is.

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The old body design with an open truck bed was more conducive to taking video. I am not sure how helpful they are, but here are a few:

http://www.youtube.com/watch?v=PtI0E8eP8uk

http://www.youtube.com/watch?v=sDqM7FISJeM

http://www.youtube.com/watch?v=uCbXzO0cvts

http://www.youtube.com/watch?v=kdTxTR-Zdyg

3. Front sway bar: What diameter? Solid? If hollow, what wall thickness?

33 mm solid

4. Rear sway bar: What diameter? Solid? If hollow, what wall thickness?

7/8" solid

[Ron Sutton]

Excellent. Thanks for those answers & the video.

I'll input all the data & be back on here in a few days. Would you measure the height from the ground to the CL of the rod end on each side of your panhard bar & post for me?

[AutoX_a_Truck?]

Excellent. Thanks for those answers & the video.

No problem. I really appreciate your help!

I'll input all the data & be back on here in a few days. Would you measure the height from the ground to the CL of the rod end on each side of your panhard bar & post for me?

When my dad and I mapped out the front suspension I figured those measurements would be important so they were actually included in the PDF I posted under the row with "Panhard Ride Height" obtained by measuring to the center of the rod ends.

The axle end (on the driver's side) is 9 5/8" and the frame end (on the passenger side) is 6 5/8"

The frame side is adjustable upward in 1" increments, with the 6 5/8" height the lowest setting, but modifications could be made to either end if necessary.

[1966longroof]

I'll be following this one. I LOVE this stuff, as an old round track guy (asphalt) street stock, LLM, Modified. A person can always learn something. Tyler...I'm sure you've already done this. But take notes on Everything. Best of luck on your quest.

[AutoX_a_Truck?]

Ron, it might have been obvious anyway, but I went ahead and updated post #5 so that the information regarding the front and rear sway bars is more accurate. The top picture shows the original front sway bar and the current front sway bar look like. The bottom picture shows the rear sway bar, which is 33" long with 8 5/8" arms that have some adjustment.


I'll be following this one. I LOVE this stuff, as an old round track guy (asphalt) street stock, LLM, Modified. A person can always learn something. Tyler...I'm sure you've already done this. But take notes on Everything. Best of luck on your quest.

Thanks! I am really digging the Nova in your profile pic. My dad has a '67 SS that he has had since high school that he autocrosses.


Subscribed...

I've seen this truck\car\SUV Scout thing run in person and it is impressive. I'm certain with Ron's tutulage and Tyler's fabrication skillz and driving it'll only get faster.

Thanks! I hope to run a handful of SCCA events this season and get the Scout dialed in. I was really impressed by your car last season too.

[rentedmule]

Also following this - hoping to get some insight into new avenues for improvement on S10 front ends.

[RobNoLimit]

This should be fun. We have an S-10 here that we play with. I'll get some picts of the front end fixes. It's only a coil spring but we made big gains. Ron, I have raced with Tyler a few times. He is smart and capable, this should work out well. Tyler, kepp up the good work - see you in a few months.

[AutoX_a_Truck?]

Ron, I just wanted to check in to make sure you had all of the info you needed from my end. Thanks again for your help!


This should be fun. We have an S-10 here that we play with. I'll get some picts of the front end fixes. It's only a coil spring but we made big gains. Ron, I have raced with Tyler a few times. He is smart and capable, this should work out well. Tyler, kepp up the good work - see you in a few months.

Rob, thanks for the kind words. I would really appreciate your valuable input too. I saw a thread for the S-10 over on the Chevy Truck forum. It's a really neat setup and looks cool with the wide tires and body work.

[Ron Sutton]

Hi Tyler,

I've been busy with client design projects the last few weeks & next week too. I'll see if I can carve out some time this weekend to map out your front suspension. But I have reviewed & analyzed your suspension issues.

I have some observations about Your Scout's handling characteristics that are clear from watching the videos. Thanks for those by the way. As Lance will tell you ... I am very visual ... and need photos and/or videos. I've spent 35 years watching race cars, roll angle, travels & tire angles.

From your videos, it is clear ...
a. Your Scout has too much roll angle for the camber you're running.
-OR-
b. You need more camber for the roll angle you're running.

c. Your front geometry only provides a moderate amount of camber gain in full dive. Not enough for the high roll angle you're running. So your outside front tire does not have a good contact patch when turning. In fact, when you turn the steering hard & fast, the contact patch narrows immediately. I am estimating about 40-45% contact patch loss. So your outside front tire is going from 11.5" of contact patch ... to 6". Since the rear tires still have a 12.5" contact patch (or close to it) ... the truck goes into an instant push.

d. The inside front tire has a decent contact patch because ... the inside wheel is losing camber as it lifts ... due to the high roll angle ... which is actually helping it. Often guys have optimized the camber for the outside front tire and have the inside tire working poorly. Your situation is the opposite.

e. You have a soft spring package which is letting the truck suspension travel a lot. That part I like, but you don't have a happy suspension package.

f. You have a high degree of roll angle from a combination of weight, higher CG and insufficient sway bar size.

g. You have a slight mismatch in front & rear roll angles. Ideally we want the front roll angle to be .3° to .4° less roll angle than the rear. This creates a balanced handling competition vehicle that is disengaging the inside rear tire more than the inside front tire. Yours is off a little. It is rolling slightly less in the rear than the front ... I'd say around .2° more in the front ... which is about .5°-.6° from ideal. What this does is keeps the inside rear tire too engaged ... and unloads the inside front tire to a higher degree ... contributing to your push condition.

h. The final ... but BIG issue, is your front shock valving doesn't have enough low-speed rebound. Meaning the front shocks let the inside front suspension roll too much and come up too quick when you step off the brakes. Ideally for AutoX & road courses, you need the shock valving to "tie down" the front end down through the roll through zone. And when the shocks do "let go" and let the front come up, it needs to happen slower. Otherwise it unloads the inside front tire ... adding to the push condition. You're probably running the shock rebound valving soft for more exit grip, but there are other, better ways of getting exit grip without killing the middle of the corner with a push.

So, before we get into changing roll centers, camber, caster, etc ... you need to pick a path for your suspension strategy. There are two good routes to go. And each strategy will need a different roll center and have different needs for optimum geometry.

#1 is a conventional low front travel/high roll angle set-up. You already have the high roll angle. For this, you would need stiffer front spring rates, reduce the compression travel on dive & keep the soft sway bars. Then you'll need to increase the camber gain & caster in the front geometry to work well with the higher roll angle.

#2 is a modern high front travel/low roll angle set-up. You already have the high front travel. For this, you would need bigger, meaner, stiffer sway bars, reduce the roll angle from the estimated 3° to around 1.5°. Then you "may" need to increase the camber gain & caster in the front geometry ... but not by much. When you roll the truck 1.5° less ... that's adds 1.5° dynamic camber to the outside tire. You will still want to optimize the camber & caster settings, but it won't need as big of a change as it needs with the high roll angle you have now.

Each has its pros & cons. If you're not clear on them, I'll be happy to provide insight. But if you're clear, pick a path and let's work on the whole suspension package along with the roll center & front suspension geometry.

[Mateospeed]

Ron Sutton is the singular most helpful source of suspension design and tuning information I've ever seen.

That is all.

[AutoX_a_Truck?]

Hi Tyler,

I've been busy with client design projects the last few weeks & next week too. I'll see if I can carve out some time this weekend to map out your front suspension. But I have reviewed & analyzed your suspension issues.

Ron, thanks for the response. I really appreciate your generous input. I understand you are busy with many other very important projects so no rush, I will wait patiently.

I have some observations about Your Scout's handling characteristics that are clear from watching the videos. Thanks for those by the way. As Lance will tell you ... I am very visual ... and need photos and/or videos. I've spent 35 years watching race cars, roll angle, travels & tire angles.

I am amazed at how much information you were able to gather from the videos. These two videos might simply be redundant so I am not sure if they are very helpful, but I figured I would include two more short videos of autoX runs:

http://youtu.be/tewKtS1f57E
http://youtu.be/dnA8TmygFLk

Are there any particular on board shots that would be particularly useful to capture at future events?

From your videos, it is clear ...
a. Your Scout has too much roll angle for the camber you're running.
-OR-
b. You need more camber for the roll angle you're running.

c. Your front geometry only provides a moderate amount of camber gain in full dive. Not enough for the high roll angle you're running. So your outside front tire does have have a good contact patch when turning. In fact, when you turn the steering hard & fast, the contact patch narrows immediately. I am estimating about 40-45% contact patch loss. So your outside front tire is going from 11.5" of contact patch ... to 6". Since the rear tires still have a 12.5" contact patch (or close to it) ... the truck goes into an instant push.

It used to be much easier to take photos and videos of the suspension in action. Here is a shot of the old setup without tall ball joints, which used the stock style S-10 shock with a heavy rate conventional spring that did not allow much travel.

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d. The inside front tire has a decent contact patch because ... the inside wheel is losing camber as it lifts ... due to the high roll angle ... which is actually helping it. Often guys have optimized the camber for the outside front tire and have the inside tire working poorly. Your situation is the opposite.

e. You have a soft spring package which is letting the truck suspension travel a lot. That part I like, but you don't have a happy suspension package.

f. You have a high degree of roll angle from a combination of weight, higher CG and insufficient sway bar size.

To avoid potential confusion down the road, which might frustrate the turning process I wanted to make a note regarding the front sway bar. In post #5 I included a picture that represents the former and current front sway bars. The former front sway bar in the top of the photo is a stock style S-10 piece, 28mm in diameter. That sway bar was in play in all of the videos provided. The current front sway bar in the bottom of the photo is 33 mm in diameter, but it was only recently installed this winter. I have not tested the current 33 mm front sway bar yet.

g. You have a slight mismatch in front & rear roll angles. Ideally we want the front roll angle to be .3° to .4° less roll angle than the rear. This creates a balanced handling competition vehicle that is disengaging the inside rear tire more than the inside front tire. Yours is off a little. It is rolling slightly less in the rear than the front ... I'd say around .2° more in the front ... which is about .5°-.6° from ideal. What this does is keeps the inside rear tire too engaged ... and unloads the inside front tire to a higher degree ... contributing to your push condition.

h. The final ... but BIG issue, is your front shock valving doesn't have enough low-speed rebound. Meaning the front shocks let the inside front suspension roll too much and come up too quick when you step off the brakes. Ideally for AutoX & road courses, you need the shock valving to "tie down" the front end down through the roll through zone. And when the shocks do "let go" and let the front come up, it needs to happen slower. Otherwise it unloads the inside front tire ... adding tot he push condition. You're probably running the shock rebound valving soft for more exit grip, but there are other, better ways of getting exit grip without killing the middle of the corner with a push.

I will have to try and refer back to my tuning notes for exact numbers (I cannot access them at the moment), but for my quickest lap at the GG autoX, the front shock settings were adjusted just below full stiff for both rebound and low speed compression (somewhere in the range of -6 to -2). In the rear I typically run closer to full soft low speed compression (somewhere in the range of -26 to -20) and somewhere in the middle for rebound (somewhere in the range of -15 to -10). Admittedly, I have struggled with shock tuning in the past. Generally, based on advice that may or may not have been accurate, I ran as much rebound as possible and started at full stiff compression and backed off until my times started to slow down. I really hope to make it to a test and tune event this season because tuning shocks is tricky with just 3-5 runs. In the future I also hope to have better luck using the very easy to follow tuning guide you posted in Lance's thread.

I posted a link to my quickest lap in post #1, but here is the link again for reference to the above statement regarding shock settings:

http://youtu.be/R9o9UwR99fE

Wow! That was a very clear, concise, and alarming snapshot of my suspension that I probably never would have determined on my own.

So, before we get into changing roll centers, camber, caster, etc ... you need to pick a path for your suspension strategy. There are two good routes to go. And each strategy will need a different roll center and have different needs for optimum geometry.

#1 is a conventional low front travel/high roll angle set-up. You already have the high roll angle. For this, you would need stiffer front spring rates, reduce the compression travel on dive & keep the soft sway bars. Then you'll need to increase the camber gain & caster in the front geometry to work well with the higher roll angle.

#2 is a modern high front travel/low roll angle set-up. You already have the high front travel. For this, you would need bigger, meaner, stiffer sway bars, reduce the roll angle from the estimated 3° to around 1.5°. Then you "may" need to increase the camber gain & caster in the front geometry ... but not by much. When you roll the truck 1.5° less ... that's adds 1.5° dynamic camber to the outside tire. You will still want to optimize the camber & caster settings, but it won't need as big of a change as it needs with the high roll angle you have now.

Each has its pros & cons. If you're not clear on them, I'll be happy to provide insight. But if you're clear, pick a path and let's work on the whole suspension package along with the roll center & front suspension geometry.

Ron, I borrowed this from your Lateral-g thread, and I think it convinced me a modern high front travel/low roll angle setup is the way to go. If I am understanding it correctly, the major disadvantage you listed for modern high front travel/low roll angle setups (susceptible to dive bomb passes in door-to-door racing) would not really be an issue since I do not race door to door. Are there any other factors specific to my vehicle that I should consider aside from those listed above and below? If not, I think implementing a modern high front travel/low roll setup is my preferred choice, but I am open to input.


Conventional:
• Stiff front springs
• Small, soft sway bars
• More Roll
• Less Pitch

Old School – Let it Roll
• Moderate to High Roll Angle (3 to 6 degrees)
• Front suspension doesn’t compress much on corner entry. (3/4” to 1-1/4”)
• Work the outside tires for grip & work the inside tires less so it will turn.

Drawbacks:
• Too much roll angle overworks the outside tires in corners & underworks the inside tires.
• The tires heat up quicker & go away quicker, providing a better short run set-up.
• After tires “come in” the car is “knife edgy” to drive.
• Very line sensitive … drivers say, “can’t drive it just anywhere” … meaning it handles poorly out of its optimum groove.
• As the track grip increases & the car rolls more … these problems magnify.
• When it rolls a lot & you brake hard, the inside rear tire has no grip. So to prevent from being loose on entry you must run stiffer front springs.
• The stiffer front springs make the car tight/pushy in the middle … requiring the driver to brake more and run slower corner speeds.

-----------------------------------------------------------------------------------------

High Travel:
• Soft front springs
• Big, stiff sway bar in front
• Known as SS/BB … soft spring/big bar … if no bump stop or coil bind is utilized.
• Same concept used in conjunction with travel stops: Bump Stops or Coil Bind
• Less Roll
• More Pitch

New School – Get the nose on the ground & run the car flatter
• Roll angle is minimal, controlled primarily by the sway bar in front & stiffer rear suspension. (1 to 1.75 degrees)
• Front suspension travels a LOT in dive (compress) to put maximum load & grip on front tires. (3” +)
• Load the outside tires only slightly more than inside corners for optimum 4 tire corner grip.

Disadvantages:
• Even when optimized … it still can not be driven as deep on corner entry as a conventional set up.
• When racing door-to-door in a field of race cars running a mixture of set-ups, the SS/BB set-up is susceptible to dive bomb passes.

Advantages:
• Flatter Roll Angle works the tires more evenly.
• The tires heat up slower & last longer … making a better long run set-up as the tires are “good” way longer.
• Less line sensitive … drivers say, “I can drive it just anywhere” … meaning any line on the track.
• As the track grip increases … the advantages show more.
• The soft spring/high travel front end puts creates maximum grip on front tires for highest cornering speeds.
• Will produce faster cornering speeds & quicker lap times over conventional set-up, all other things being equal.

[Ron Sutton]

Don't pay the ransom ... I'm back. :)

Hey Tyler,

I ran the calcs in the software and am posting 2 graphs below. One at ride height & the second "dynamic" in dive & roll. For now, I am estimating your dive at 2.75" and your roll at 2.5°. This isn't dead on accurate but close enough to learn, discuss & move forward.


Ride Height:
91595



Dynamic in Dive & Roll:
91596

[Ron Sutton]

Tyler,

We have a lot to cover & some things to figure out. I'm clear on some things & not on others. I'm going to map out what I see and let's start some discussion to help us both figure it out.

What I see so far ...
1. You have a lot of stuff right or close to right. I think you're on track with your thoughts and plans.
2. You have some things not correct ... some are close ... others are not.
3. You have several things off a little ... enough so that it pushes too easy.
4. We may ... or may not ... find you have one big thing "off." And that would be what I call dynamic toe, which is a combination of ackerman, static toe out & "bump out" (toe out from bump steer). I can't tell for sure, because we haven't mapped out the steering ... yet. But that spindle has anti-ackerman in it ... so I have concerns.

5. The two fenderwell camera videos in post #1 ... show me different dynamic tire angles ... which has me a bit perplexed. Are they from the same day? Were there any changes between those runs?

* The geometry shows plenty of camber, but one of the videos shows the car driving on the outside edge of the outside front tire. Any changes between the date of the video & the date of the geometry capture?


6. If I understand the order of things ...
a. You had stiffer springs & the 28mm sway bar, then ...
b. Went to softer front springs & the same 28mm bar, then ...
c. You switched to the 33mm bar ... but haven't run it yet.
... is this correct ?

If so, "a" was your "conventional set-up" ... "b" was a high travel & high roll set-up ... and "c" will be somewhat of a high travel/low roll set-up.

7. Even though the two fenderwell camera videos in post #1 show me different dynamic tire angles ... I still think you have the wrong geometry for that much roll angle. But it sounds like you want to go the high travel/low roll angle route ... so the geometry change will be less.



I typically shoot for about -1 degree of static camber, 0 toe in/out, and according to the FasTrax Adjustable Caster Camber Gauge I can currently register about 8.5-8.6 degrees of caster.
8. My calcs ... and the software show you have much higher caster than your specs ... and different from side to side. 11.5° on the left & 10.6° on the right. So either your ball joint measurements are off or your caster measuring process is off.




I am also battling a relatively high scrub radius due to my 17x11” wheels with just 4.25” backspacing. Using the method in Lance’s thread, I measured the scrub radius at 4 13/32”
9. That is a ton for an AutoX vehicle. Where it hurts the most is in the tightest corners ... and especially if you have to give the truck some additional steering input when you're in the corner. You can band aid this some by running an higher/wider entry line ... turning in later & harder ... and apexing later. This will help, but the solution is longer control arms & deeper back spaced front wheels to get that scrub radius down closer to zero.


10. There are several differences in your geometry settings from side to side. What this does is make the dynamic geometry different on LH turns versus RH turns ... which makes the truck handle differently on LH turns versus RH turns. This is common ... especially in production car ... but never good. My focus is on "how bad is it" and does it merit reworking & TLC'ing the geometry points to correct it.

Yours is off significantly. Your RC migrates to the left quite a bit (21") on LH turns ... and a ton (184") on right hand turns.

11. The front roll center is too low one direction (Not 25" .... .25" below ground level) ... and way too high (5"+) the other direction. If all other things were neutral, this would make the front end of the truck roll more on LH turns & less on RH turns. With the numbers I'm seeing, the effect won't be small, so you should be feeling it & seeing it.

P.S. All things are not neutral, as you have 3" of split in the panhard bar. I'll address that in the next post.

For a 2.5°-3° high roll angle/Autox set-up I feel around 1.5"± above ground would be closer to optimum. Both directions obviously. For a 1.0°-1.5° low roll angle set-up, you'll want to be around zero (ground level).

.

.

This is hard left hand turn ...
91597

.

.

This is a hard right hand turn ...
91598

As you can see ... there is some work to do ...





I typically shoot for about -1 degree of static camber, 0 toe in/out
12. We definitely want to switch to running some toe out, but we need to look at the whole picture. Static toe out helps give the inside tire "some" slip angle ... which makes the tires have more initial turn in grip ... and the steering becomes way more responsive.

13. We also need to look at what your bump steer does through your realistic travel. Have you bump steered each side individually yet?

14. The only reason to run dynamic toe (ackerman, static toe-out & "bump out") is to force the inside front tire to achieve the optimum slip angle ... for optimum grip. This is HUGE ... especially for cars running tight road courses & autoX tracks. There is no "one best setting" because it varies with both tire design and suspension strategy.

Low Front Travel/High Roll Angle suspension set-ups work the inside front tire less ... and require a larger combination of ackerman, toe-out & bump out. High Front Travel/Low Roll Angle suspension set-ups work the inside front tire more ... and require a smaller combination of ackerman, toe-out & bump out. But both need to be tuned until optimum front tire grip is found.

15. Remember earlier when I said ...
"You have a slight mismatch in front & rear roll angles. Ideally we want the front roll angle to be .3° to .4° less roll angle than the rear. This creates a balanced handling competition vehicle that is disengaging the inside rear tire more than the inside front tire. Yours is off a little. It is rolling slightly less in the rear than the front ... I'd say around .2° more in the front ... which is about .5°-.6° from ideal."

What this means is as you work out your spring rate & sway bar rate combo ... you need rear springs & sway bars to achieve about .3°-.4° more rear roll angle than front. As an example, i have a set up that runs the front end at 1.2° & the rear at 1.55° roll angles. This is keep the inside front tire working better & disengage the inside rear tire "to a specific degree" to help the truck turn. Make sense?

16. Also mentioned earlier ...
The final ... but BIG issue, is your front shock valving doesn't have enough low-speed rebound. Meaning the front shocks let the inside front suspension roll too much and come up too quick when you step off the brakes. To achieve your AutoX goals, you need front shock valving with both stiffer low speed rebound valving & some degree of rebound valving at zero, before it moves.

17. As you correct all these things to make the truck turn better ... if nothing is done in the rear, you'll lack forward bite off the corners. Two things that will need to be addressed are shock valving (stiffer low speed rebound) and the height of the IC for "lift & plant" leverage.

After you read all of this over ... digest it, answer my few questions ... and let's figure out what we need to do make your truck an even better handling machine.

Next I'll post some info on tuning what we call "Split" in the panhard bar to achieve neutral handling.

[Ron Sutton]

Tuning the split in a panhard bar for neutral handling

For most road course & autocross applications, a watt's link works well and is the preferred choice of many. I agree & support this ... but because I'm a tuner, I prefer a panhard bar ... but only if it is height adjustable on both sides & centered in the chassis. This is not a thread to steer someone towards or away from either. Just an understanding of how they work & how they can & can not be tuned.

Pros & cons of Watt’s links:
• Pro: Does not cause different roll centers, roll resistance or tire loads on LH & RH corners.
• Con: Can not be tuned to provide different roll resistance or tire loads on LH & RH corners.

Pros & cons of panhard bars:
• Con: If simply set level, causes different roll centers, roll resistance & tire loads on LH & RH corners.
• Pro: Can be tuned with simple angle change to achieve neutral & equal roll resistance & tire loads on LH & RH corners.
• Pro: Can be tuned to provide different roll resistance & tire loads on LH & RH corners.

The natural tendency for a panhard bar (mounted to the housing on the left & the chassis on the right):
• In LH turns, the left side rod end raises only a small amount with tire extension & the right side rod ends lowers significantly with suspension compression. This moves the roll center down dynamically on LH corners.
• If the panhard bar had been level at 10”, the math could look like this: LH 10.25” & RH 9” = DRC 9.625” & 1.25” split
• In RH turns, the left side rod end lowers only a small amount with tire compression & the right side rod end raises significantly with suspension extension. This moves the roll center up dynamically on RH corners.
• If the panhard bar had been level at 10”, the math could look like this: LH 9.75” & RH 11” = DRC 10.375” & 1.25” split

The split is the same both directions … at 1.25” in this example:
• But the DRC (dynamic roll center) is ¾” lower on LH corners than on RH corners.
• The car rolls more on LH corners … making the car more free or looser.
• The car rolls less on RH corners … making the car more tight or pushy.
• If the panhard bar mounting is reversed, everything above is reversed too.
• This can be corrected easily. More on the “how to” later.

The irony is … the torque steer from centered 3-link, 4-link, torque arm & truck arm suspensions … behave the opposite under power on corner exit. So under power the combination of torque steer & panhard effects are neutralizing each other to some degree … but just on corner exit. You would still have the car behaving more freely or looser in the entry & middle of LH corners … and more tight or pushy in the entry & middle of RH corners. So it’s not the ideal solution by any means.

But with an offset 3-link … if the top link is offset to the right the correct amount to counter the torque … you end up with zero torque steer under power. Combine this with a Watt’s link or “Balanced Panhard Bar” and you will have even loading throughout the corner … on both left & right hand corners. :)

What is a Balanced Panhard Bar?
We already know that Watt’s links do not cause different roll centers or loads on LH & RH corners … and they can not be adjusted to do so. If you’re running a Watt’s link you will have even loading. If you’re running a panhard bar … with an offset 3-link … you need to tune the panhard bar angle to neutralize the effects discussed above and have a balanced panhard bar set-up. It is easy to do, but needs to be done.

To counter the typical panhard bar effects, you simply run angle … also known as split … in the panhard bar … with the left side lower & right side higher. (Assuming the panhard bar is mounted to the housing on the left & the chassis on the right.) For discussion purposes only, let’s say you run the same 10” roll center but with a 1/2” split. The left side would be 9.75” & right side 10.25”. The dynamic results during cornering would look like this:
• In LH turns: LH 10” & RH 9.25” = DRC 9.625” & 0.75” split
• In RH turns LH 9.5” & RH 11.25” = DRC 10.375” & 1.75” split

This next part throws people off as it is a little challenging to digest:
• The dynamic roll centers do not change with panhard bar split.
• But the differences in dynamic panhard bar angles … change the chassis roll resistance & tire loading when cornering.
• The lower levels of split on LH corners & the higher levels of split on RH corners … balance the handling left & right.
• Of course the numbers above are just an example & the split needs to be fine tuned on any race or track car.

So Ron … why don’t you run a Watt’s link?
Simple answer really. There are some variables that sometimes call for the race car to load the tires more one direction of corner & less the other direction. An adjustable panhard bar lets me fine tune the balance of tire loading.

Situations to tune balance with panhard bar split:
1. Car not 50/50 balanced side to side. Some cars are left heavy due to driver placement.
2. Some tracks have more rights. Some tracks more lefts.
3. Some tracks have high speed lefts & low speed rights … or vice versa.
4. Some tracks have more banked lefts & flatter rights … or vice versa.
5. Some track have off-camber corners, combined with flat and/or banked corners.

At the end of the day, winning races is about overcoming the challenges of the track better than your competitors. If I have a tuning tool that lets me tune for any of these 5 conditions better than my competitors that don’t have this tool … that’s an advantage I’ll take.

We ran a course with 7 right hand turns and only 2 lefts. One left was banked & the other was tight & flat. We used several tools to “wedge” the opposite direction of oval track racers. This gripped up the RH turns & freed up the LH turns. We had amazing grip on all the right hand turns. The banking providing “ok” grip for the first left turn. And freeing up the other super tight left corner made us faster there too. We were faster in 8 out of the 9 corners … won a lot a of races … and won two championships at that track. :)

---------------------------------------------------------------------------------

Whew! That’s a lot to take in. Let’s summarize it.

1. Centered 3-link, 4-link, torque arm & truck arm suspensions experience torque steer under acceleration.
2. Offset 3-links, if offset correctly, do not experience torque steer.
3. Watt’s links do not cause different roll centers or loads on LH & RH corners … and cannot be adjusted to do so.
4. Panhard bars do cause different roll centers & loads on LH & RH corners … but can be adjusted back to neutral & balanced.
5. Panhard bars can be run neutral & balanced … or tuned to load the tires differently if needed.

---------------------------------------------------------------------------------

With a centered 3-link, 4-link, Torque Arm or Truck Arms & a Watt’s link:
• You will have even loading on entry & middle for both left & right hand corners.
• You are stuck with torque steer on corner exits.

With a centered 3-link, 4-link, Torque Arm or Truck Arms & a adjustable panhard bar:
You can use the panhard bar angle to effectively counteract "torque steer" … to a degree. The keys to doing this are simple:
• Keep the center height where you want the roll center.
• Lower the side you want to load the tire more on & raise the other side the same amount.

This strategy is always a compromise. But the suspension already had a compromise.
You’re just shifting where the compromise is.

Think of it this way:
• If you eliminate 100% of the torque steer, you will have 100% of the effects provided by an unbalanced panhard bar set-up.
• If you balanced panhard bar set-up 100%, you will have 100% of the of the torque steer.
• Most racers shoot for a 50/50 balance and then tune for track conditions.
• You can always shift the balance to gain here & give up there.

With an offset 3-link & a Watt’s link:
• You have zero torque steer and can achieve a “Balanced Panhard Bar” for even loading throughout both left & right hand corners. :)

With an offset 3-link & an adjustable panhard bar:
• You have zero torque steer and can achieve a “Balanced Panhard Bar” for even loading throughout both left & right hand corners. :)
• Plus, you can tune tire load balance with panhard bar split if the situation calls for it.

Make sense?

[AutoX_a_Truck?]

After you read all of this over ... digest it, answer my few questions ... and let's figure out what we need to do make your truck an even better handling machine.

Ron, thanks again for your assistance. I almost always end up reading your posts multiple times, but you certainly are very good at providing concise explanations that break down the concepts. It was a lot of information to digest, but I think I have some grasp of the outlined concepts. Below are my answers to each of your questions, which I hope will clear up any confusion.


4. We may ... or may not ... find you have one big thing "off." And that would be what I call dynamic toe, which is a combination of ackerman, static toe out & "bump out" (toe out from bump steer). I can't tell for sure, because we haven't mapped out the steering ... yet. But that spindle has anti-ackerman in it ... so I have concerns.

My Dad started experimenting with modifying the spindle steering arms. That project is finally to a mock up stage. Here is a picture. The spindle itself is the same, but the overall length of the steering arm is approximately 1" shorter than before, and the steering arm is bent as far as brake rotor clearance allows, which is about 2” further inward. The plan is to reset the alignment and then check and adjust bump steer as necessary. The basic goal is to try and at least eliminate the anti-Ackerman steering to achieve some percentage of 100% Ackerman.

91662


5. The two fenderwell camera videos in post #1 ... show me different dynamic tire angles ... which has me a bit perplexed. Are they from the same day? Were there any changes between those runs?

One video was from GG Des Moines July 2012 and the other was from GG Kansas September 2012. I do not believe any chassis or suspension components were changed between the two events. It is possible that there was a slight change in the front end alignment between the two events though.


* The geometry shows plenty of camber, but one of the videos shows the car driving on the outside edge of the outside front tire. Any changes between the date of the video & the date of the geometry capture?

Those suspension view videos were taken with the old truck body. The truck body was slightly lighter in the front and lighter in the rear. The underlying chassis components are the same though.


6. If I understand the order of things ...

a. You had stiffer springs & the 28mm sway bar, then ...

This was the original setup that started as a stock style S10 front suspension with a conventional spring, stock style shock, and drop spindle.


b. Went to softer front springs & the same 28mm bar, then ...

At this point the RideTech Triple Adjustable Coilovers were installed with a 10" long 450 lbs/in spring (softer than the previous conventional spring). The stock style 28 mm S10 sway bar was used, albeit with aftermarket end links. This is the setup used in all of the videos I posted.


c. You switched to the 33mm bar ... but haven't run it yet.
... is this correct ?

Correct.


8. My calcs ... and the software show you have much higher caster than your specs ... and different from side to side. 11.5° on the left & 10.6° on the right. So either your ball joint measurements are off or your caster measuring process is off.

The caster measurements were only recently taken using a newly acquired Fastrax gauge. I hope the error was in the cater measuring process. I will look into verifying both measurements. When my Dad and I mapped out the suspension, we spent the better part of a Saturday and Sunday making sure the measurements were accurate.

91663


9. That is a ton for an AutoX vehicle. Where it hurts the most is in the tightest corners ... and especially if you have to give the truck some additional steering input when you're in the corner. You can band aid this some by running an higher/wider entry line ... turning in later & harder ... and apexing later. This will help, but the solution is longer control arms & deeper back spaced front wheels to get that scrub radius down closer to zero.

I would like to redo the entire front end with better components and ditch the heavy, cast Cragars for a set of 18” light weight forged wheels with deep backspacing, but for the time being I cannot afford to change or upgrade my wheels and all of the components so I am stuck reusing components in a different way or targeting aspects that can be tweaked or fabricated.


10. There are several differences in your geometry settings from side to side. What this does is make the dynamic geometry different on LH turns versus RH turns ... which makes the truck handle differently on LH turns versus RH turns. This is common ... especially in production car ... but never good. My focus is on "how bad is it" and does it merit reworking & TLC'ing the geometry points to correct it.

Yours is off significantly. Your RC migrates to the left quite a bit (21") on LH turns ... and a ton (184") on right hand turns.

11. The front roll center is too low one direction (25" below ground level) ... and way too high (5"+) the other direction. If all other things were neutral, this would make the front end of the truck roll more on LH turns & less on RH turns. With the numbers I'm seeing, the effect won't be small, so you should be feeling it & seeing it.

P.S. All things are not neutral, as you have 3" of split in the panhard bar. I'll address that in the next post.

For a 2.5°-3° high roll angle/Autox set-up I feel around 1.5"± above ground would be closer to optimum. Both directions obviously. For a 1.0°-1.5° low roll angle set-up, you'll want to be around zero (ground level).

Dependent upon your input, I think tweaking the upper and lower control arms pivot points should be able to provide two benefits. First, (if I am picturing the dimensions correctly) I think it should be possible to square up a large amount of the front end geometry by tweaking the horizontal and vertical position of the upper and lower control arm pivots on either side. For instance, I double checked, and the ball joint pivots to control arm pivots are the same on either side. Second, where feasible, it might also be beneficial to improve the geometry rather than simply square it up. That said, I am not the expert here so I will defer to your suggestions.


13. We also need to look at what your bump steer does through your realistic travel. Have you bump steered each side individually yet?
I will add measuring bump steer to the "to do list."


15. Remember earlier when I said ...
"You have a slight mismatch in front & rear roll angles. Ideally we want the front roll angle to be .3° to .4° less roll angle than the rear. This creates a balanced handling competition vehicle that is disengaging the inside rear tire more than the inside front tire. Yours is off a little. It is rolling slightly less in the rear than the front ... I'd say around .2° more in the front ... which is about .5°-.6° from ideal."

What this means is as you work out your spring rate & sway bar rate combo ... you need rear springs & sway bars to achieve about .3°-.4° more rear roll angle than front. As an example, i have a set up that runs the front end at 1.2° & the rear at 1.55° roll angles. This is keep the inside front tire working better & disengage the inside rear tire "to a specific degree" to help the truck turn. Make sense?

Yes, the concept makes sense.

[AutoX_a_Truck?]

To counter the typical panhard bar effects, you simply run angle … also known as split … in the panhard bar … with the left side lower & right side higher. (Assuming the panhard bar is mounted to the housing on the left & the chassis on the right.)

It sounds like the current panhard bar split is the opposite of ideal. The housing mount on the left is a fixed design set at 9 5/8" and the chassis mount on the right is adjustable in 1" increments from 6 5/8" to 9 5/8"

At first, we usually just ran the panhard bar level but at one point it was disconnected and put back in the lowest hole (probably for no good reason). It should not be a huge problem to alter the current design of the panhard bar by either tweaking the mounting points or by fabricating new mounting solutions.

[Ron Sutton]

Hi Tyler,

We got a lot of conversation points going. I'll try to keep it concise & on track.

#4 - I like the "shorter arm" as that will speed up the steering. If you're not moving the steering box, arms & centerlink assembly back the same amount ... that will reduce the ackerman ... so it requires more ackerman be built into the spindle offset. Moving it in 2" may be overkill. Realize the centerlink adds some ackerman as it moves forward during steering (as the steering arms rotate).

You need to either calculate it out or test it physically on the truck. With zero toe-in or toe out, if you turn the wheels left ... and make the RF at a 25° angle ... what angle is the LF at? I often target 4-5° more.

#5 - It does make sense now. the two tracks could have easily had different grip levels and created different roll angles. Also, if you changed any alignment specs as you mentioned, could affect it too.

Later on ... switching back to the heavy body ... played a big roll in your roll angle being higher. Additional weight, up high, has to be dealt with.

#6 - Makes sense. When you went to softer springs & kept the small sway bar, roll angle increased along with dive travel. Now you've put on the bigger sway bar, which is a good move.

#8 - Either the ball joint measurements are off or the caster measurements are off, because they don't match. Double check & see if you can find which is correct.

#9 - I completely understand the budget issue. Work to optimize everything else & make it work as well as you can with the scrub radius you have now. Then, down the road, if you want to improve this area, you'll need to make new control arms & get deeper back spaced wheels.

#10 & #11 - You are on track. It is not that hard to square up the measurements ... and while you're at it, make some improvements. Lance Hamilton did this to his Monte and made big gains. Read his thread on how to do this HERE (https://www.pro-touring.com/threads/98063-Need-a-little-help-figuring-something-out).

#13 - Doing the bump steer could show a small or big problem. So that is good it's on the "to-do" list.

#15 - You've already done something to improve this ... by switching to a larger front sway bar. Without running the calcs, we don't know if this achieves the optimum front to rear roll angles. And if you're going the low roll angle route, you have a decision to make in "how far". Let's say the 33mm bar reduces your roll angle from 3.0° to 2.5°. Do you want to fine tune that combo? ... or go to a bigger splined sway bar in the front and shoot for a roll angle of 2.0°, 1.5°, etc? ... and tune your spring & bar package around that?

[AutoX_a_Truck?]

Ron, I got your message so I figured I would check in even though I do not have much of an update. I am glad to see you are back on the forum, and I hope that your business venture is going well. I have not been home or had time to work on the Scout since February as I have been very busy with school, which is finally winding down after 20+ years. Once I graduate in mid-May, I should be able to devote some more time to the Scout. In the meantime, my Dad has tweaking the steering geometry and other components to get bump steer under control. I will also have the opportunity to attend two autocross events on June 1 and June 29 for gathering more testing data and video footage. Before I start, I had a carryover question from a previous post:


16. Also mentioned earlier ...
The final ... but BIG issue, is your front shock valving doesn't have enough low-speed rebound. Meaning the front shocks let the inside front suspension roll too much and come up too quick when you step off the brakes. To achieve your AutoX goals, you need front shock valving with both stiffer low speed rebound valving & some degree of rebound valving at zero, before it moves.

Ron, I forgot to ask this earlier . . . What sort of inputs of measurements, video footage, or other inputs are necessary to determine shock valving? And for the upcoming events are there any video angles or data I should focus on collecting?


#4 - If you're not moving the steering box, arms & centerlink assembly back the same amount ... that will reduce the ackerman ... so it requires more ackerman be built into the spindle offset. Moving it in 2" may be overkill. Realize the centerlink adds some ackerman as it moves forward during steering (as the steering arms rotate).

You need to either calculate it out or test it physically on the truck. If you turn the wheels left ... and make the RF at a 25° angle ... what angle is the LF at? I often target 4-5° more.
The results were as you indicated above. With the wheels turned to the left and the RF at a 20° angle, the LF is also at a 20° angle (+ or - 1°). However, by further modifying the steering arm, the results improved and are closer to the target of 4-5°


#8 - Either the ball joint measurements are off or the caster measurements are off, because they don't match. Double check & see if you can find which is correct.

I still need to set everything up for re-measuring the ball joint dimensions.


#13 - Doing the bump steer could show a small or big problem. So good it's on the to-do list.

The tie rods were pointing above the instant center, which caused the wheel to bump-out when moving up, and bump-in when moving down. Using a very helpful Longacre document and a different centerlink, it was possible to get the bump steer under control using a design similar to the bottom diagram. For the time being though I do not have super accurate measurement numbers.

94470

Here is a pic of the centerlink in mock up and a pic of the final product.

94471

94472


#15 - You've already done something to improve this ... by switching to a larger front sway bar. Without running the calcs, we don't know if these achieves the optimum front to rear roll angles. And if you're going the low roll angle route, a decision to make is "how far". Lt's say the 33mm bar reduces your roll angle from 3.0° to 2.5°. Do you want to fine tune that combo? ... or go to a bigger splined sway bar in the front and shoot for a roll angle of 2.0°, 1.5°, etc? ... and tune your spring & bar package around that?

I probably would prefer to look into further reducing the roll angle with a larger splined sway bar if the 33mm sway bar only reduces the roll angle to 2.5°. I largely base this off information in some of your other posts, and under the assumption that you think it would be a “good” idea to further reduce the roll angle. In the past, I looked into a larger splined sway bar from Speedway Engineering. I think it would be a relatively affordable way to upgrade the sway bar and build in greater adjustment. The main problem will be packaging. If a larger splined sway bar is placed in the same position as the stock style sway bar, it might require arms with multiple complex bends to fit because the packaging is rather tight. That said, I think it should be feasible to fabricate a solution, and once the initial fabrication was done it would be relatively easy and affordable to fine tune the sway bar in the future.

This from an earlier post:


17. As you correct all these things to make the truck turn better ... if nothing is done in the rear, you'll lack forward bite off the corners. Two things that will need to be addressed are shock valving (stiffer low speed rebound) and the height of the IC for "lift & plant" leverage..

I apologize up front, because once again I am potentially opening up a new can of worms . . . But once the front end is in a happier place, my Dad and I thought it might be time to look at redesigning the rear suspension. When we first built the chassis it was a “use what we had on hand” project, closely followed by a “go with what is easy to package and fabricate” motto. I figure it should not be too hard to package a homemade offset 3 link for the rear that can offer more adjustability and less unsprung weight among other attributes.

[Ron Sutton]

Hi Tyler,

I'm back on the Forums. I know you're busy with other stuff. When you're ready to pick up our discussion, just PM me.

:cheers:

[AutoX_a_Truck?]

Hi Tyler,

I'm back on the Forums. I know you're busy with other stuff. When you're ready to pick up our discussion, just PM me.

:cheers:

Ron, aside from what I posted in #25, I do not have much of an update, but I wanted to check in because I now have some free time to devote to my Scout II project.

I think the steering setup is now in a good place with minimal bump steer. My Dad fabricated a trick roller bearing setup for the idler arm to finish it off.


Also, the upper ball joints can be adjusted to be at least 1" taller than in the previous measurements.

I have an autoX event on June 1st. Before then my to do list includes taking more accurate measurements of the front ball joints (and possibly other components) so that the dimensions match the measured caster angle. It should also be relatively easy to fix the panhard bar split, which is the opposite of what you suggested in post #21. I also posed a few questions in post #25 regarding making the most of the event to gather the most useful data possible. Finally, as always, I am open to your suggestions and input.

Thank you,
Tyler

[Ron Sutton]

Hi Tyler,

We still have a lot of moving parts in this discussion, so I’m trying to keep them straight & in order.


In the order you need to attack them …


A big issue is the geometry not matching side to side. As I outlined earlier, this makes the dynamic geometry different on LH turns versus RH turns ... which makes the truck handle differently on LH turns versus RH turns. Your RC migrates to the left quite a bit (21") on LH turns ... and a ton (184") on right hand turns. The front roll center is too low one direction (.25" below ground level) ... and way too high (5"+) the other direction. If all other things were neutral, this would make the front end of the truck roll more on LH turns & less on RH turns. This is a significant variance and needs to be fixed first. Otherwise we’re wasting our time with the tuning.

It is not that hard to square up the measurements ... and while you're at it, make some improvements. Lance Hamilton did this to his Monte and made big gains. Read his thread on how to do this HERE (https://www.pro-touring.com/threads/98063-Need-a-little-help-figuring-something-out).

I ran your geometry calcs a several ways and correcting it is pretty simple. It’s work … but it’s not complex. What I am going to suggest is not how I’d do it, because I would be raising all the control arm mounts significantly & building my geometry different. But that is very involved & we’re going to keep this simple.

You will want to modify & shift all of the control arm pivot points on the left side … to match the right side … which includes raising the left side ride height to match the right side. This will get all of the front end geometry performing & acting the same on left hand & right hand corners. Then use upper ball joints that are ¾” taller and it will place your roll center in a sweet spot for your high-travel/low-roll suspension strategy.

In the chart below I have the truck turning left … and made the roll angle less at 2.0° … and you can see the RC is .3” above ground. I ran the roll angle from 1.5° to 2.5° and the RC height doesn’t change much, but the migration (left & right) is less with lower roll angles.

96120


Next, you will want to dial in the ackerman. A rule of thumb “starting point” I use often is 25° & 30°. Set your toe-out first … to 1/8” out total (1/16” each side). Do this with the steering absolutely centered. Then turn wheels either direction … until the outside tire is at 25° steering angle. Measure the steering angle of the inside wheel & let me know where it ends up. We will fine tune this number … next … with static toe-out & bump steer settings.

Before you measure & adjust bump steer, set the static camber at -0.5° & static caster at 9° on both front wheels. That is my baseline recommendation for you. Many people may tell you to run more camber or less caster, but that is not the case with a high travel front end. The challenge will be not ending up with too much camber.

Lance’s thread contains some great info on measuring bump steer where he simply clamped a straight edge & laser to the brake rotor and pointed the laser at a paper target placed a set distance ahead of the axle CL for simple math conversions. When you’re using a bump steer gauge like I and many have … you’re working with 2’ … 12” in front of the axle CL & 12” behind.

Making the laser distance 20’ from the axle CL makes the math real easy … because all you do is reduce your measurements by 10, by simply moving the decimal point. In other words if the laser shows a .300” variance 20’ away … it’s only .030” at the wheel. The farther away the target is, the bigger the variance will show. This makes it easier to see, measure & fine tune it more accurately. But most people don’t have a shop large enough to do that. So if you use 10’ simply dived by 5 … 8’ dived by 4 & so on.

For your specific goals & this truck … you will want to measure bump steer from 4” compression of your suspension to 2” of extension (at the tip of the spindle). Measure & reference everything with the spindle at ride height. Let’s consider 3” of compression your max compression travel and make this your priority point. 3” of compression is what we’ll reference in all of our conversations as “full dive.” For extension, even though you’re measuring to 2” … for track purposes, we only care about 1”. So, let’s consider 1” your full extension number for reference in discussions.

Many people think you want zero bump steer, but that’s not accurate for competition vehicles. We want bump-out in dive (suspension compression) to increase the toe-out for a higher slip angle of the inside front tire for increased grip of that inside tire. And we want the toe-out to reduce as the front end rises (suspension extension) to assist in adding forward bite/grip for corner exit.

Only as a baseline starting point, I typically find the sweet spot where I’m getting .030” of “bump-out” on each side … .060” (1/16”) total in full compression (3”). “Bump-out” is slang for toe out increasing from bump steer during compression. It is ok if you see a lot of “bump in” during dive/compression. I don’t get concerned unless it exceeds .060” each side or .120” total at 1”. I can not say what your final bump steer needs to be until I know your ackerman situation. Even then, you’ll want to fine tune this to achieve optimum front tire slip angle & grip … which can only come from track testing. I’ll guide you on “how to do this” later.

I see your Dad has already modified find your tie rod length and mounting points on the centerlink to tame the bump steer beast. You “may” find your tie rod length and mounting point on the centerlink needs to change again … and may not.

Let’s save the shock valving & panhard bar angle discussion until we have these projects on track. Then I’ll share with you the hows & why’s of modern race track shock valving. Plus I’ll show you how to tune the panhard bar for neutral handling … or to load one side more or less depending on the track.



:cheers:

[AutoX_a_Truck?]

Time to revive this 2 year-old thread! This last winter brought a snowball of upgrades. The front rotors and pads were shot, so my Dad and I decided to do a brake upgrade all around with larger and wider bolt on circle track style rotors along with Wilwood Dynalite calipers. The old 7.5” GM 10 bolt was maxed out so we picked up a Ford 8.8”, and it only made sense to build a new suspension for the rearend. We designed and fabricated an offset 3 link with a torque link. So far I think it has worked very well, and it seems like a major improvement. As for the brakes, they are better, but I still need to get used to them to push them to their full potential.

https://static1.pt-content.com/images/pt/2016/06/CZHM-1.jpg

https://static1.pt-content.com/images/pt/2016/06/u0Xu-1.jpg

The old Michelin PS2s on the rear finally wore out, and they are so expensive and difficult to find that I decided to go with 315/35R17 Nitto NT05s on the rear same as the front. They are approved for 12.5” wide wheels, but that is definitely the max because they look a bit funny like the import guys who stretch tires. So far the forward bite seems better, but the sidewalls are much stiffer so I will have to experiment more with pressures. Four runs at the last autoX just was not enough to get the footprint and lateral grip/feel where I wanted. The Nittos are way off compared to the newest and even previous generation of 200 treadwear tires, but they will have to do for now.

Over the last 2 years the front suspension geometry has been tweaked slightly in an attempt to get the geometry very close to the same right to left. But the goal is to find some free time this summer to completely redo the front suspension measurements to get a solid baseline and make any necessary changes. It should be much easier and a bit more accurate the 2nd time around just because we will have some experience and a better idea of how the whole process works. I would also like to get the Scout back on some 4 corner scales to get a good baseline weight.

Pictures:

https://pattersonprints.smugmug.com/Motorsports/Kansas-City-Region-SCCA/2016-KCRSCCA-Solo-Event-3/i-RPGxpgp

https://pattersonprints.smugmug.com/Motorsports/Kansas-City-Region-SCCA/2016-KCRSCCA-Solo-Event-3/i-kfWTxpx/A

https://pattersonprints.smugmug.com/Motorsports/Kansas-City-Region-SCCA/2016-KCRSCCA-Solo-Event-1/i-x7WxXMs/A

https://pattersonprints.smugmug.com/Motorsports/Kansas-City-Region-SCCA/2016-KCRSCCA-Solo-Event-1/i-8BDDH7R/A

https://pattersonprints.smugmug.com/Motorsports/Kansas-City-Region-SCCA/2015-KCRSCCA-Events/2015-KCRSCCA-Solo-Event-12/i-DRtcTZ5/A

https://pattersonprints.smugmug.com/Motorsports/Kansas-City-Region-SCCA/2015-KCRSCCA-Events/2015-KCRSCCA-Solo-Event-12/i-vcvHXs7/A

Here are a few front suspension videos of the from an SCCA event last season:

https://youtu.be/xlkyaAfg8p0

https://youtu.be/WBA1VjhrrVc

And here are a rear suspension videos of the new offset 3 link in action from a recent SCCA event:

https://youtu.be/cdkWAx2g9-M

https://youtu.be/GFvP0RDfNwU

https://youtu.be/F4SYGHSKz6I

[BK2LIFE]

Time to revive this 2 year-old thread!


sure is !!

8 years later, anything new?