HellBoy - No Limit C10

[coolwelder62]

Awesome lob on the truck Rob.Kevin say's that thing work's great.

[RobNoLimit]

I did say it would be a driving thread after all. haha. Last weekend was the "ROUE 66 " autocross. We helped put this on for the city here and it went really well. Robert and Trish Byrd (Racing Byrds) did the coarse layout and supplied the timing and P.A. equipment. And I have to say they did a great job. The guys from K.R.O.P.S. (Keep Racing Off Public Streets) ran the pits, shagged cones, and did tech. The event went great, weather was great, crowd was great, Rob's radiator, not so great. On my fourth run at about 10 am, some type of evil material made it's way into, and I mean INTO, the radiator. and, as you would guess, put a hole in it. A BIG hole. We first tried the stop leak. Not a chance. The good news, if there was any, is that I was litterally one block from my shop. So, I ran, yes, on foot, to the shop to check to see if I had a radiator in stock, No. But, I did have a core of the correct size. So, I ran back to the stadium, got the truck, topped it off with water, and drove it over to the shop. Pulled the old rad and built a new one. The radiator is a bit more complex than normal, double pass with the water pump mounting built into the lower tank, and with the mounting, took me about three hours to build and install. Thinking of Mike Maier using the track forklift to pull the motor and then win a championship a few weeks ago kept me moving quickly. When I left the autocross 60.0 was fast, when I got back it was 57.8's. It was 2:30 and my run group had just finished so I had to wait. Good, choke down a burger and a coke. In a few runs I got down to a 56.777. then Matt Alcalla ran a 56.768, .009, are you kidding? Then Danny Pinard in his Pedders prepped 2013 SS Camaro put down a flawless 56.458. What? is that right? Matt dropped a tenth, and then our run group got the final go. On my second, and final run of the day, I ran 56.341. I could hardly believe it. Other notable were Casey in his third gen Camaro at 56.844 and Bill Speed in the Black Widow S-10 at 56.782. The moral here, "Never Say Die"

[Ron Sutton]

Nothing like a good thrash repairing your car to get the heart pumping!

Congrats on the win !

.

[RobNoLimit]

OK Ron lets talk about this beast. The rear is a torque arm set up, and I have two main approach areas for the link bars. Here's some basics. The wheel base is 107" ft wt 1665, or 52.8%. rear wt is 1460 or 47.2%. 3125 total (this is without me in it, add 195 lbs, very close to 50/50 added ft/rr) The C.G. hieght is appx. 16.65". I'd like to discuss the different link bar locations. The usual bars in this type of set up would be in one of the lower positions. During the build I had a thought that there might be some advantage of having the link bars at the same hieght as the axle center line. The link bars are 24" eye/eye. For now, I want to talk about acceleration/braking forces, (not any rear steer) Before I taint the water with my own thoughts, and experience with the truck in real life, I'd like to hear your thoughts on these different bar positions, anti-squat, and in the mix, torque arm length. Please be kind to my humble chicken scratch here.

[Ron Sutton]

OK Ron lets talk about this beast.

The rear is a torque arm set up, and I have two main approach areas for the link bars.

Here's some basics. The wheel base is 107" ft wt 1665, or 52.8%. rear wt is 1460 or 47.2%. 3125 total (this is without me in it, add 195 lbs, very close to 50/50 added ft/rr) The C.G. hieght is appx. 16.65".

I'd like to discuss the different link bar locations. The usual bars in this type of set up would be in one of the lower positions. During the build I had a thought that there might be some advantage of having the link bars at the same hieght as the axle center line. The link bars are 24" eye/eye.

For now, I want to talk about acceleration/braking forces, (not any rear steer) Before I taint the water with my own thoughts, and experience with the truck in real life, I'd like to hear your thoughts on these different bar positions, anti-squat, and in the mix, torque arm length. Please be kind to my humble chicken scratch here.

Hey Rob,

Best drawing I've seen in awhile.
Everything was super clear, except the torque arm mounts up front. Are there 5 mounting points horizontally ... allowing you to use different torque arm lengths?

Also, need to confirm the torque arm is decoupled. Or is it mounted on a pivot/slide?

The more I think about it ... for the discussion we're going to have ... I need to see the front mounting. I'm very visual, can you post a few photos?

[RobNoLimit]

Yes Ron, 5 mounting points horizontally, front to rear. The measurements are from the rear axle centerline forward. The connection from chassis to torque arm is with a shackle assembly. The bottom, chassis mount, uses a a urathane bushing and sleave, there are 5 steel busshing shells (tubing) welded in a row. Then end of the torque arm has 5 sphericle bearings in bearing shells welded in a row. The urathane bushing allows the shacle to rotate forward/backward and keep the torque arm in line, the bearing mount allows the axle to tip side to side without binding in the front shackle mount. I'll take some specific picts thursday. Thanks.

[RobNoLimit]

Here's some picts from the underside. I must confess, I did not indicate all of the link bar moumt locations. I only listed the locations that I have current log data with. I think for the initial discussion this will be cleaner. The first pict is of the shackle mounts on the chassis. - simple hat bushings and a sleave fit in. The second picture is of the front section of the torque arm, and you can see the row of bearings. pict three is the link bar mount on the housing. And the last pict is the link bar mount on the chassis. - some of the pict quality is not so good but I think this will give you a good visual.

Crap, well the picts loaded in reverse order. - you'll get the idea.

[Ron Sutton]

Hey Rob, thanks for the photos.

I learn & understand things best when I see them. It would have took 10,000 words for me to understand this. The 4 photos made it super clear.

OK Ron lets talk about this beast. The rear is a torque arm set up, and I have two main approach areas for the link bars.

Here's some basics. The wheel base is 107" ft wt 1665, or 52.8%. rear wt is 1460 or 47.2%. 3125 total (this is without me in it, add 195 lbs, very close to 50/50 added ft/rr) The C.G. hieght is appx. 16.65". I'd like to discuss the different link bar locations.

The usual bars in this type of set up would be in one of the lower positions. During the build I had a thought that there might be some advantage of having the link bars at the same hieght as the axle center line. The link bars are 24" eye/eye.

For now, I want to talk about acceleration/braking forces, (not any rear steer) Before I taint the water with my own thoughts, and experience with the truck in real life, I'd like to hear your thoughts on these different bar positions, anti-squat, and in the mix, torque arm length. Please be kind to my humble chicken scratch here.

First, I have never ran a torque arm with what I think of as the "lower links" ... mounted at axle CL ... making them "center links"

I read about this concept from Herb Adams years ago. But I do not have any first hand experience to know what they will do.

There are WAY more factors to how a link suspension works than anti-squat. In fact there are a dozen key factors. Some overlap with anti-squat, but clarify the cause & effect more. Some have nothing to do with anti-squat:
1. Anti-squat percentage / AS % lift & squat effects on acceleration & deceleration
2. Horizontal IC location / Length of swing arm
3. Vertical IC location / Affect on AS
4. Resultant thrust angle
5. Upper & lower link horizontal separation / Control
6. Upper & lower link vertical separation / Torque loading percentages
7. Upper link placement / Torque steer
8. Upper link angle / Torque steer
9. Upper link angle / Degree of lift vs pull
10. Lower link angle / Degree of lift vs push
11. Lower link angle / Side forces
12. Lower link angle / Rear steer

And this is if we stick to traditional 3-link, 4-link & torque arm suspensions. There are more factors if we utilize torque absorbers on any of the links and/or decouple the top links. Since you & I are discussing this, I save the complete tutorial for another time, and just focus on the items you want to discuss … which still covers a lot of ground.

1. Anti-squat is a crude method to measure a suspension’s leverage & resistance to squat or lift the rear suspension. Many folks don’t take into account the g-forces effect on the car … they just look at the suspension … which is a mistake.

Under acceleration, the car wants to “pitch” (lift the front & compressing the rear). The guide is anything less than 100% anti-squat allows the suspension to compresses on acceleration & anything more than 100% anti-squat causes the suspension to extend/lift on acceleration. There are some other factors often not discussed that affect the math and the result to a degree, but the concept is spot on.

Obviously, under braking the car wants to “pitch” the other way (compress the front suspension & lift the rear). Again, the anti-squat percentage plays a role here too, as higher AS % increase this effect, and lower AS % reduces the effect.


2. The horizontal IC location determines the length of swing arm, which experience has shown me to be the most critical factor in defining the characteristics of the rear suspension. As anyone who has played around with anti-squat calculations knows, you can achieve the same AS% with the IC location at different lengths. The AS% matters, but the IC length matters more.

The horizontal IC location determines the length of swing arm … which is simply telling us how long the lever is. Lever is the important word here. Realizing it is a lever is the key to understanding & tuning rear suspensions. And realizing it is operating in a dynamic condition … with constantly changing loads on the lever … is another key to optimum tuning.

The effects are clear & simple:
• The longer lever loads the rear end & tires with more weight, slower & over a longer period of time of acceleration.
• The shorter lever loads the rear end & tires with less weight, quicker & over a shorter period of time of acceleration.

Any time we need the traction to last longer (higher power cars) we’re moving the IC farther forward, making the lever longer. Anytime we have less power, and need to “help” the car get going, we run move the IC closer to the rear axle, making the lever shorter.

Where the lever is lifting … in relation to where the weight is … is critical. The weight bias (horizontal CG location) of the car plays a huge role in where we place the IC. For most of the higher powered stuff I work with (500-1000hp) we are placing the IC under the CG or in front of it. On lower power cars, making the swing arm shorter, moving the IC back, helps achieve weight transfer.

So on a car with 600hp, 108” wheelbase, 52% front weight … making the CG at 56.16” ahead of the rear axle … I’m usually targeting a horizontal IC location in the 50”-60” range as a starting point. Other factors will come into play as we fine tune this car, including the rear suspension.

The CG height plays an important, but secondary role. If we’re running the lower links level, for zero rear steer, their height is controlling the IC height. If we need to tune on this, and desire to keep zero rear steer, then we need to raise or lower these lower links equally front & rear. This is course requires forethought when someone is building their 3, 4 or torque link suspension.


3. Of course the vertical IC location has an effect on AS percentage. Assuming the IC doesn’t move horizontally;
• The higher you raise the IC, the more the suspension will load the rear tires, lift the front end … but push the car forward less.
• Taken too high in drag cars, causes violent wheel stands.
• If too high in track cars, the tires have early grip but lose grip later during corner exit.
• The lower you place the IC, the less the suspension will load the rear tires, lift the front end … but push the car forward more.
• Taken to excess in drag cars or track cars, causes tire spin.


4. Most everyone is familiar with the line drawn from the center of the rear tire contact patch through the IC. Anti-squat & rise percentages are calculated from where this line crosses the CG line. Not everyone is familiar that this line is the resultant thrust angle. The resultant thrust angle is the actual direction the tire & suspension are driving the car.

The lower the angle, the less effect on loading the tire, less lifting of the car … and the more the tire is driving the car forward providing it has enough traction for the application. The higher the angle, the more effect on loading the tire, more lifting of the car … and the less the tire is driving the car forward.

We fine tune the traction by:
• Moving the IC horizontal to control how quick, how hard & how long the tires are loaded.
• Moving the IC Vertical to control how much load is lifting & how much is pushing.


6. The upper & lower link vertical separation affects the torque loading percentages of the links. Most folks know that under acceleration the lower link pushes & upper link pulls. But what is really happening is the lower links push & drives the car forward, the upper link lifts the car, loading the tires.

If the upper & lower links are placed the same distance apart from the rear axle centerline … say 5” each for conversation … the rotational torque from the axle housing is split 50/50. 50% of the torque driving the car forward & 50% lifting the car & loading the tires. If you change the relationship to 75/25 … say by making the lower link 7.5” below the rear axle centerline and the upper link 2.5” above the rear axle centerline … then you 75% of the torque driving the car forward & 25% lifting the car & loading the tires.

This is just one factor of the whole equation. But it is a common reason why two cars with the same link angles & AS % percentage don’t perform exactly the same.

Key Tip: When you have more torque to rotate the housing, you need less torque directed to lifting & more going to push/drive the car forward. When you have less torque to rotate the housing, you need more of that torque directed to lifting & less pushing the car forward.

In Pro/Stock level powered drag cars, with more torque to rotate the housing, moving the lower links farther away from the axle CL and the upper links closer to the axle CL … helps reduce violent wheel stands. Here is a sample in this photo.



In very low powered drag cars, with less torque to rotate the housing, placing the lower links closer to the axle CL and the upper links farther away from the axle CL … helps load the tires harder for quicker launches. Here is a sample in this photo.



* I should clarify ... MANY suspension brackets built for street cars are placing a higher priority on floor pan clearance than placement of the links for optimum torque distribution.

In high powered Track Cars, with really big slicks, I tend to lean more towards 60/40 or 70/30 split ... shorter on top.

In AutoX & Track Cars on TW200 street tires, with hard sidewalls, I find the need to plant the tires a little harder. For this reason I recommend closer to the 50/50 torque distribution … providing you have enough floor plan clearance for the taller upper brackets on the housing.

Guys reading along with us ... Remember: If you run your lower links level for zero rear steer ... the height of your lower links are the height of your IC. Design accordingly.

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So … Rob ...

A. If you’re running your “lower links” level with the axle CL, that would mean there is a lesser degree of torque pushing & a higher degree of lift.
B. This is probably providing more traction on AutoX tracks.
C. But with the short swing arm lever, the traction may, or may not, last as long as you want/need. (Corner length affects this)
D. I also suspect you have less torque steer during braking & acceleration.
E. But hey, this is all just theory, because I’ve never run this set-up.
F. Right now you’re the only one I know with experience with this set-up. What’s it doing ?

[RobNoLimit]

A. yes, that is the current set up.
B. Also yes but - C. loss of traction in long sweepers and at corner exit (some of this may be cuased by the drivers foot)
D. Almost no torque steer
E & F. This is my first torque arm set up, and I haven't had any "good"information to help, so, I'm sure I have made some mistakes

Before we go much further, I want to clarify I.C. locations when using a Torque Arm. My understanding (although I have heard and read many others) is that the I.C. for a T.A. car would be at the intersection of A) a line passing vertically though the chassis mount of the torque arm, and B) the vector line moving forward though the link centerline.

Here is a drawing to illustrate (the way I understand it) two different link bar locations that I have commonly used, and the effective A.S. percentages.

So...Ron...

A. would you agree with this as the correct method to determined the I.C.? - and If not, how about a quick explanation of the correct way. That way we are both on the same page.
B. I agree with the explanation of concepts above, so if I have the I.C. correct, we'll get into whats happening, and the story of how it got to this point.

[linkstar69]

This thread is an excellent read.

[Ron Sutton]

A. yes, that is the current set up.
B. Also yes but - C. loss of traction in long sweepers and at corner exit (some of this may be cuased by the drivers foot)
D. Almost no torque steer
E & F. This is my first torque arm set up, and I haven't had any "good"information to help, so, I'm sure I have made some mistakes

Before we go much further, I want to clarify I.C. locations when using a Torque Arm. My understanding (although I have heard and read many others) is that the I.C. for a T.A. car would be at the intersection of A) a line passing vertically though the chassis mount of the torque arm, and B) the vector line moving forward though the link centerline.

Here is a drawing to illustrate (the way I understand it) two different link bar locations that I have commonly used, and the effective A.S. percentages.

So...Ron...

A. would you agree with this as the correct method to determined the I.C.? - and If not, how about a quick explanation of the correct way. That way we are both on the same page.
B. I agree with the explanation of concepts above, so if I have the I.C. correct, we'll get into whats happening, and the story of how it got to this point.

Hey Rob,
It's always a good sign when the theories & the results match.

Until now I had seen/heard two theories & methods on determining the IC of a torque arm suspension. Yours add a third twist. Let’s cover those first, then I share what I learned from testing.

1. Some folks believe the IC is where the line of the lower links converge with the line from the axle through the torque arm pick up point.
2. Some folks believe the IC is where the front point of the torque arm lifts up on the chassis and the lower links only affect roll steer.
3. Your drawing, if I understand it correctly, is working off a similar theory to #1 … but that the IC is always at the length of the torque arm pick up point.

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Now I’ll throw you a curve ball. I have found none of these three are completely correct and all three are partially correct. Huh? I know. Stay with me.

First, I have zero drag race experience with a torque arm suspension. All of my experience with tuning, testing & racing the torque arm suspension are in road racing. Second, I learned a long time ago to treat anti-squat percentage as small player in the 12 factors in how a rear suspension works. So a target anti-squat percentage is never my goal. “Resultant thrust angle” is way more important. The AS % matters … but it’s just a byproduct of getting the desired resultant thrust angle.

Third, and this is a reach at first, the torque arm suspension is rare in that its lift point and IC are not necessarily the same. WTH? I know. Be patient with me and I’ll make it all make sense & come together. Here goes …

A torque arm applies lifting force at the pick up point. Period. This point is not affected by the lower links. The lower links angle or height, do not change where the torque arm is applying its lifting force. Nothing stops the torque arm from lifting at its pick up point. Nothing changes where the torque arm is lifting from its pick up point. If you embrace that, the rest will make sense.

The lower links still help define the instant center. The lower links angle & height … and the line projecting through them … converge with the line from the axle through the torque arm pick up point … to form an instant center. This defines the “swing arm” characteristics of the rear suspension. This is the arc the suspension pivots & rotates on. But it does not change where the lifting force is. The lifting force is still at the pick up point of the torque arm. This is what is rare. And this is what confuses most folks. We are all used to the IC being the point where the lifting force is. With a torque arm, it is not.

We can change how the torque arm suspension works and how it loads the tires by moving the lower links, but we’re not changing the point of lifting force. So what does the lower links affect? A lot!

The lower link vertical separation from the axle CL affects the torque loading percentages of the links. Most folks know that under acceleration the lower links push. The lower links push & drive the car forward. The closer the lower links are to the axle CL the less torque is applied to pushing the car forward. Therefore more torque is transferred through the torque arm to lift. Conversely ... the farther the lower links are from the axle CL the more torque is applied to pushing the car forward. Therefore less torque is transferred through the torque arm to lift.

So in this way, moving the links higher off the ground & closer to the axle CL, moves the IC up, creating a higher AS %. And the result is “almost” the same as achieving a higher AS% with all other rear suspension models. More force from the housing rotation is applied to lifting & less to pushing. But the torque arm is still applying lifting force at the pick up point. That point does not change with lower link adjustments.

Conversely, moving the links lower to the ground & farther from the axle CL, moves the IC down, creating a lower AS %. And the result is “almost” the same as achieving a lower AS% with all other rear suspension models. Less force from the housing rotation is applied to lifting & more to pushing. But the torque arm is still applying lifting force at the pick up point. That point does not change with lower link adjustments.

I’m going to go off-track & discuss 3 & 4-links for a moment, but it will help to provide clarity. Let’s say we have a 3 or 4 link suspension … with the upper & lower links both 5” from the axle CL … with angles to form the IC 50” in front of the rear axle & 7” off the ground.
• If we move all of the links down 2.5” at the housing … to where the lower links are 7.5” from the axle CL & the upper link(s) is/are now 2.5” above axle CL … but we adjust the front pivot points so the IC is still 50” in front of the rear axle & 7” off the ground … we will have less lifting force & more pushing force … because of the change in torque distribution.
• If instead, we were to move all of the links up 2.5” at the housing … to where the lower links are 2.5” from the axle CL & the upper link(s) is/are now 7.5” above axle CL … but we adjust the front pivot points so the IC is still 50” in front of the rear axle & 7” off the ground … we will have more lifting force & less pushing force … because of the change in torque distribution.
• But the IC never changed. The anti-squat never changed. The IC & anti-squat matter … but they are not everything.

Now let’s discuss lower link angle. Adjusting the lower link angle so the front is higher than the rear … or the angle is running uphill going forward as I like to say … moves the IC up, creating a higher AS %. And the result is “almost” the same as achieving a higher AS% with all other rear suspension models. More force from the housing rotation is applied to lifting & less to pushing. But the torque arm is still applying the lifting force at the same pick up point. That point does not change with lower link adjustments.

Conversely, adjusting the lower link angle so the front is lower than the rear … or the angle is running downhill going forward … moves the IC down, creating a lower AS %. And the result is “almost” the same as achieving a lower AS% with all other rear suspension models. Less force from the housing rotation is applied to lifting & more to pushing. But the torque arm is still applying lifting force at the same pick up point. That point does not change with lower link adjustments.

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While we’re on the subject of lower link angle, we need to discuss the effects of rear steer on traction (or roll steer as some call it). First the basics for our readers following along:
• Lower links at an angle running uphill going forward creates a rear steer effect as the body & chassis roll during cornering. Larger uphill link angles produce higher degrees of rear steer.
• As the car achieves roll angle, the rear steer effect helps the car to turn while cornering, by pushing the outside tire rearward, the inside tire forward and both tires pointing to the outside of the corner. This is rear steer. This also adds a slight loosening effect.
• Lower links at an angle running downhill going forward creates a counter rear steer effect, by pushing the outside tire forward, the inside tire rearward and both tires pointing to the inside of the corner. This is counter rear steer. Larger downhill angles produce higher degrees of counter rear steer.
• As the car achieves roll angle, counter rear steer effect reduces the car’s turning ability. This adds a slight tightening effect.

* This next explanation does not apply to drag cars if they have controlled their body rotation with preload, springs and/or sway bars. This applies to all other cars that run on Road Courses, AutoX. Street, etc … where you are trying to accelerate out of corners under power.

Even though running the lower links at an uphill angle … applies more force applied to lifting & planting the tires harder … there is also the different action of rear steer happening simultaneously … providing a counter effect. The small gain in traction from increased lifting force (for a shorter duration) is over powered by the larger rear steer effect loosening the car up. The typical result is more grip at throttle pick up, but loss of traction at some point trying to exit the corner under power.

When the loss of traction occurs … is defined by how much rear steer is in the car and how long the corner exit is (therefore how long cornering grip must be maintained). On tight corners it possible to achieve a setup that provides rear steer & good exit grip. I find small amounts of rear steer on short, small corners, can work good, as long as everything else is optimized.

We run into problems is when we:
• Get greedy with the amount of rear steer utilized.
• Run any rear steer on high speed, long sweeping corners.

For these reasons, I suggest:
• Rear steer can be good tuning tool for short tracks with small tight corners.
• Avoid any rear steer on big tracks or road courses with long, fast sweepers.
• In fact, counter rear steer can be used effectively on tracks with primarily long, fast sweeping corners.

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Guidelines for torque distribution:
• When you have more engine torque to rotate the housing, you need less torque directed to lifting & more going to push/drive the car forward. When you have less engine torque to rotate the housing, you need more of that torque directed to lifting & less pushing the car forward.
• Also: When you have softer sidewall tires you need less torque directed to lifting & more going to push/drive the car forward. When you have stiffer sidewall tires, you need more of that torque directed to lifting & less pushing the car forward.
• Engine power output, curve, tire design, track conditions, etc … all play a role in defining the optimum setup any given day at the track.
• The key is finding the optimum balance for each individual application.

In high powered Track Cars, with wide slicks, I tend to lean more towards 60/40 or 70/30 split of link split ... shorter on top. In AutoX & Track Cars on TW200 street tires, with harder sidewalls, I find we need to plant the tires a little harder. For this reason I recommend closer to the 50/50 torque distribution … providing you have enough floor pan clearance for the tall housing brackets.

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In summary, Torque Arm suspensions act & respond similar to other suspension models with one exception. The pick up point of the torque arm is always where the lifting force is applied, regardless of where the IC is.

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We have not discussed your placement of the horizontal torque arm pick up point and the resultant thrust angle. I believe that will be the primary key to getting your grip to “stay with you” longer on corner exits.

Your wheelbase is 107" with 52.8% rear weight & 47.2% front weight. That makes your CG at 50.5” in front of the rear axle. Your current torque arm pick up points range from 30” to 36”. We could load the rear tires with more weight, slower & over a longer period of time of acceleration ... with the longer lever of a torque arm pick up point farther forward. In my experience the happy widow is going to be in the 45”-55” range.

Of course, we need to discuss your lower link mounting, get into what’s happening with your handling now … and the story of how it got to this point.

Let’s start there. Catch me up on what's happening & how it got there.