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Tincup
08-13-2015, 12:03 PM
I'm getting ready to start modifying my truck chassis and have a basic question. When you set up the bare chassis, you set it level, and at desired ride height, either on the shop floor or frame table. Do you actually set it at desired ride height or do you add a couple inches to account for when all the weight is put back on the chassis? I would think if I have a bare chassis, and I want a 6" ride height under the main rails, I should set it at say 8" so when everything is back together ( all the weight back on it ) it will be at my desired 6". I am running all coilovers so I will have some adjustment. Any help is appreciated...

dirty rick
08-13-2015, 12:15 PM
Ride height is determined by the geometry designed into your suspension. You can replace the shocks with solid struts to maintain that height during construction. There is a sweet spot in every suspension design for ride height and that should not be deviated from by much (at all). If you are buying suspension components ask for design specs you then build the frame with the right drop to put the body where you want it at ride height.

RobNoLimit
08-14-2015, 04:48 AM
It's all in the math. We like to set the chassis level (easier to measure from), and then calculate the position of the front and rear center lines at ride height. As Rick said, a Coil-Over manufacturer will be able to give you the 'Open', Closed', and 'Ride-Height' specs of their shock. Use the 'Ride-Height' dimensions to plan out the mount locations for your desired outcome. Remember to factor in the tire diameter here as well.

Tell you what, we are starting a build for an 89 C1500, I'll post up some picts and drawing to help out.

RobNoLimit
08-14-2015, 06:27 AM
1. We're building a chassis for an 88-98 short bed. Our customer has a list of wants, 315 front tire, 345 rear tire, 5"R.H. (bottom of rail), Air ride, full drop, tow a small trailer, 800 hp LSX, 6L80E, .... OK, well, at No Limit, if you're going to actually drive it, we will build in the suspension stops so that the frame WON'T hit the ground.First compromise, full drop will be 1" off the ground. Everything else on the list is fine. We start with wheelbase, R.H. of the main rail, and the tire sizes. 1/2 of the tires diameter is the center to the ground. We subtract .400" for tire squish at R.H.

RobNoLimit
08-14-2015, 06:31 AM
2. Rear kick height. Start at the axle CL height, add 1.500" for half of the axle tube (assuming 3" axle), then add 4" for up travel (we add in another .500" for a bumpstop here, that I did not include in the simplified drawing), and then another 4" for the height of the rear frame rail (yours may vary, 4" to 5" is normal)

Rod
08-14-2015, 06:37 AM
this thread is fun!!!

RobNoLimit
08-14-2015, 06:40 AM
3. For the front rail height, you need some more info. The IFS you choose will have a 'sweet spot' or recommended ride height. ** Here's a tip - If the company your going to buy an IFS from can't give you this information, Your dealing with the wrong people. Hang up the phone.** On our No Limit Wide-Ride IFS (shameless plug), we spec from the 'top' of the rail down to the spindle CL. 5" for Std. spindle, 3" for drop spindle. On really low trucks, we prefer a drop spindle vs. raising the crossmember too high (this can upset motor height, driveline angles, and raise the CG) - as long as there is good ground clearance from the bottom of the crossmember to the ground.

With this info to start with, we can begin to layout a plan for the frame rails and suspension. I'll show you some more next week. Have a great weekend - Please leave a comment or two, or a question. If this is of no interest, I'll stop here.

Peter Mc Mahon
08-14-2015, 07:16 AM
. If this is of no interest, I'll stop here.[/QUOTE]
Oh ya, this is of no interest at all. One of the guys at the top of the game explaining things from the beginning. Just cancel this thread now.
Continue on, please.......

Guyt699
08-14-2015, 07:54 AM
I am very interested in seeing what you guys do with the 88-98 C1500 chassis Rob. Suspension is next on my list!

Rod
08-14-2015, 09:26 AM
If this is of no interest, I'll stop here.


WHAT!!! dang it Rob....always starting trouble.... :cheers:

Tincup
08-14-2015, 10:27 AM
Thanks a ton Rob, I'll be doing some homework tonight. Please continue for both myself and all the other interested individuals. BTW, I am using your Fatbar on the rear.

72BBSwinger
08-14-2015, 10:39 AM
Another thing, at least this is how my brain works, is setting the upper control arm angle. Rob do you have it parallel to the ground at ride height or already starting into negative camber gain at ride height?

andrewb70
08-14-2015, 10:40 AM
Please continue! This is very helpful not only from a practical perspective but for general knowledge. I may never build a frame from scratch, but I sure would love to know how it is done.

Andrew

69_Sportsroof
08-14-2015, 06:33 PM
This is exactly the kind of advice I've been looking for. Please continue, it is very good info.

Tincup
08-16-2015, 04:38 PM
116178

Here is a pic of my IFS. The manufacturer could not provide me with the CL number because he did not have the spindles, I designed an machined my own so that I could run an OEM hub and brake setup. According to my measurements the number is 3" from the top of the frame mount to the spindle CL. My front tire is a 285-40-20 (29" dia.) so if I take half my tire dia 14.5" add in my 3" that should put the top of my frame rail at 17.5" from the ground. With a 5" rail height the bottom is at 12.5" but it all depends on the amount of kick up my frame has to determine rail to ground clearance. My chassis has a 5 5/8" kick up in the front, so that would put my ground clearance at 7.375" Does this make sense?

Dr G
08-17-2015, 08:00 AM
If that is the ultimate position of your steering rack then I'd say you're going to have some bad bump steer. The tie rod should be coincident with a line pointing to the instant center of the two control arms. Yours seems to be pointing in a very different direction.

brawls43
08-17-2015, 08:01 AM
Great info Rob! Sub'ing to follow this one.

Tincup
08-17-2015, 09:25 AM
If that is the ultimate position of your steering rack then I'd say you're going to have some bad bump steer. The tie rod should be coincident with a line pointing to the instant center of the two control arms. Yours seems to be pointing in a very different direction.

No big deal, I can flip the tie rod brackets...

XTRMEASURES
08-17-2015, 09:29 AM
Great info indeed

RobNoLimit
08-17-2015, 10:09 AM
Good to see everyone chiming in.

OK, since Tin Cup started this, I am trying to follow along with what will fit his needs best. I did notice the steering issues, and possible another. So, to help out, I have some more chicken scratch for you.

The first is a very basic plotting of the Instant Center (henceforth to be known as IC) - (three extra points for that word). Also, this shows a basic concept of bumpsteer tuning. Once the A arms are set, you can plot out the IC. Next, a line through the inner Tie Rod End (TRE), and outer TRE (see how much easier that is for me to type?) should also intersect through the IC. As for the length of the TRE - inner pivot to outer pivot - it can be plotted by drawing a line through the Upper Ball Joint (UBL) and the Lower Ball Joint (LBJ), and drawing a line through the Upper Control Arm (UCA) and Lower Control Arm (LCA) pivot points. Measing from the intersection points of these lines as they pass the TRE line will give you the length of TR needed. Note** you CAN move the Tie Rod 'in' or 'out' on the TRE line as long as the TR length is correct.

So, take a look at this.
1. Looks like A) lower the rack as much as you can - you will need engine clearance. and B)Raise the outer TRE. Now, if your going to make a new steering arm, plot out the TR legth and see if you need to move the outer TRE in or out.
2. Also, if the upper and lower A-Arm lines are very close to parallel, you may want to make the spindle 'taller', to get the lines to cross for the IC a little sooner. Raising your spindle with a new lower ball joint mount may help.

RobNoLimit
08-17-2015, 10:18 AM
More Napkin scratch.

When planning an IFS for a certain chassis, again, wheel size and ride height are right up there. I like to keep the bottom of the front crossmember close to being even with the bottom of the main rail (general rule) If the crossmember is much lower, it will be the first thing to hit the ground (5" dropped C10) If the crossmember is much higher, it will cause drastic eng/trans driveline angles, more than 5 degrees. So, there has to be a balance with the Tire/spindle/rack/crossmember to keep things working good. This is mostly food for thought. You also have to use whats available, as most of us don't have the budget to build 100% spec custom everything (Indy car)

rchaskin
08-17-2015, 10:22 AM
Awesome thread.....

Tincup
08-17-2015, 11:01 AM
While this is all good stuff, I feel we have gone off on a tangent from the original question.

Tincup
08-17-2015, 12:13 PM
116213

While researching Bumpsteer, I did come across this picture which is exactly what Rob was explaining.

brawls43
08-18-2015, 06:39 AM
Back to your original question, about setting up the frame and chassis. I do like Rob said, and set the chassis level, its easier working off a level chassis to me. Then set the front spindle height and rear axle based on ride height. So I mock up some welded rods to replace the shocks, to sit at the calculated ride height. This avoids the difference in weight of a bare chassis vs a fully loaded chassis and body. Sure you could calculate the difference in height based on the weight differences, but if you're putting the engine/trans in and doing some work, then taking it out, and your weight is changing, then things seem to shift around. Just my preference.

RobNoLimit
08-18-2015, 01:56 PM
I agree, setting building at RH, on a level plain is the easiest. OK, I'm not trying to lead away from the original question, just wanted to go a little farther.

The reason I started out on the IC explanation was to get to the next step (and to help you sort out some steering issues). The location of the IC on each side is what sets the Roll Center (RC). The roll center is the physical roll axis of the suspension/chassis/truck. ** see the drawing

As you RAISE the RC, the truck will lean LESS in a corner, BUT, the trade off is, it will also load the outside tire LESS. This will lead to a 'Push', or under-steer. - less sway bar is needed.
As you LOWER the RC, the truck will lean MORE, BUT it will also load the outside tire MORE, and have less tendency to 'push'. - More sway-bar is needed here.

On our normal performance minded build, a RC of 2" to 2 1/2" is a good starting point. You can manipulate the RC a bit, by raising and lowering the crossmember in the chassis. If the LCA is level, the RC will be appx 1/2 of the distance from the ball joint center or LCA pivot (as these two should be the same if the arm is level) to the ground. If you are building the rails, you have a chance to play with this a bit.

Rod
08-18-2015, 02:12 PM
The reason I started out on the IC explanation was to get to the next step (and to help you sort out some steering issues). The location of the IC on each side is what sets the Roll Center (RC). The roll center is the physical roll axis of the suspension/chassis/truck. ** see the drawing

As you RAISE the RC, the truck will lean LESS in a corner, BUT, the trade off is, it will also load the outside tire LESS. This will lead to a 'Push', or under-steer. - less sway bar is needed.
As you LOWER the RC, the truck will lean MORE, BUT it will also load the outside tire MORE, and have less tendency to 'push'. - More sway-bar is needed here.

On our normal performance minded build, a RC of 2" to 2 1/2" is a good starting point. You can manipulate the RC a bit, by raising and lowering the crossmember in the chassis. If the LCA is level, the RC will be appx 1/2 of the distance from the ball joint center or LCA pivot (as these two should be the same if the arm is level) to the ground. If you are building the rails, you have a chance to play with this a bit.

now where cooking!!!

Rod
08-18-2015, 02:13 PM
ummm Rob....I'm stealing your art work

Josh@Ridetech
08-19-2015, 05:41 AM
Very cool. Good info, Rob!

Red67Mustang
08-19-2015, 03:39 PM
Awesome thread! Very informative and useful for tuning the suspension. Thanks!

RobNoLimit
08-20-2015, 05:17 AM
For most builds, the front suspension is purchased or re-used, so the shock length is somewhat set. The shock mounting for the rear suspension usually has a bit more freedom. I have two general shock rules that I try to follow.

1) Try to use the longest shock possible (within reason) - but never let the shock be the limiting factor of suspension travel (this is more important in compression, we sometimes allow the shock to be the limiter in 'droop')

2) Try to keep the shock at appx 50% travel when the suspension is at RH. (+/- 5% is well within reason)

I have seen many front suspensions that use short - 3 1/2" stroke - coil-overs, and the coil-over gets the blame for the harsh ride. Here's the quick math. At RH, a 3 1/2" stroke shock has 1.75" of compression travel. It also uses a short spring, usually 7" or so. If there is 850 lbs of the left front corner, and the LCA has a .7 to 1 motion ratio, then there is appx 1200 lbs of force compressing the coil-over at RH. If the spring was pre-loaded onto the shock 1/4", or 150 lbs., then you need a 600 lb spring to hold the car up. And, it rides pretty stiff. If you had a 5" stroke shock with a 12" spring, with 150 lbs pre-load, you would use a 450 spring. These concepts are for comfort and ride quality, But, as we lean more towards a 'soft spring - big bar' set up for performance, this is a winner in for both comfort and performance.

Stroke Compressed Extended Suggested Spring Length Price
2.9" 8.725" 11.625" 8" $250 [Purchase]
3.6 9.425 13.025 8 $250 [Purchase]
4.1 10.125 14.225 10 $250 [Purchase]
5.2 11.225 16.425 12 $250 [Purchase]
6.3 12.325 18.625 14 $250 [Purchase]
6.9 13.125 20.025 14 $250 [Purchase]

I copied this from RideTech's web site. Most shock companies will list the open and closed lengths of their shocks. I like to use their 5.2" stroke coil-over on our WideRide IFS fronts, and the 5.2" or 6.3" in the rear on most trucks. Looking at the 5.2" shock, it has a closed length of 11.225", and an open length of 16.425". The suggested RH for this shock would be 13.75 to 14" (13.825" is 1/2 of the stroke.)

Up front, if you were really going for it, starting with tire height and spindle CL, you could set the RC and crossmember height, then build the rail shape to match the crossmember up front while keeping the body at it's desired RH. Then, choose the desired shock, and fab the upper coil-over mount to set the shock in it's spec RH range.

?? does that make sense?

Dr G
08-20-2015, 08:18 AM
Rob - I have read a few times now where you state not to use the shock to limit suspension travel, especially in bump/compression. Yet that is exactly how most road race cars are set up. With bump stops to tune the end of travel. I cannot speak for dirt ovals, Nascar or off road, they use different methods. Can you explain your thoughts on travel limitation? Gustave

RobNoLimit
08-20-2015, 11:45 AM
"Race" is the key word here. The street can be a lot more destructive on parts. That being said, you are correct about this, with one exception. They use thick bump rubbers on the shock shaft. On the average street/performance coil-over, when the shock is bottomed out, it's a metal-to-metal hit. - and no, I don't consider the .095" O-ring to be a damper. This metal-to-metal contact can do lots of damage to the shock, shock mounts, control arms,....... The bump rubbers you mentioned are available in different durometer ratings (hardness) and are used to tune in the suspension at the end of the travel. These can be used on the street, but they may have other effects. Most of these are 1" thick or more, and fit around the shock shaft. So, you loose some of the shocks compression travel. - A 5.2" travel shock @ 50% has 2.6" of bump travel, install a medium 1" bump rubber and now you have 1.6" of free travel and maybe another 1/4" of compressing the rubber. in other words, you lost 39% of the available compression travel. Now, if you planned to do this from the very start, you may run a 6.2" stroke shock with different mounts and set it up to get the 2.6" of compression travel, and then hit the bump rubber. ** I am working with pure shock travel numbers. If the LCA has a 70% motion ratio, 1" of shock travel = 1.42" of wheel travel.**

Most race tracks are fairly smooth, all things considered. They don't have speed bumps, curbs, off camber driveways, pot holes, sink holes...... I caution against using the coil-over as a pure travel stop to help shed off impending doom.

brawls43
08-20-2015, 11:50 AM
So do you use rubber bump stops on the frame to protect axle on frame hits? This happening before the shock fully compresses? What do you do in front?

Dr G
08-20-2015, 03:33 PM
"Race" is the key word here. The street can be a lot more destructive on parts. That being said, you are correct about this, with one exception. They use thick bump rubbers on the shock shaft. On the average street/performance coil-over, when the shock is bottomed out, it's a metal-to-metal hit. - and no, I don't consider the .095" O-ring to be a damper. This metal-to-metal contact can do lots of damage to the shock, shock mounts, control arms,....... The bump rubbers you mentioned are available in different durometer ratings (hardness) and are used to tune in the suspension at the end of the travel. These can be used on the street, but they may have other effects. Most of these are 1" thick or more, and fit around the shock shaft. So, you loose some of the shocks compression travel. - A 5.2" travel shock @ 50% has 2.6" of bump travel, install a medium 1" bump rubber and now you have 1.6" of free travel and maybe another 1/4" of compressing the rubber. in other words, you lost 39% of the available compression travel. Now, if you planned to do this from the very start, you may run a 6.2" stroke shock with different mounts and set it up to get the 2.6" of compression travel, and then hit the bump rubber. ** I am working with pure shock travel numbers. If the LCA has a 70% motion ratio, 1" of shock travel = 1.42" of wheel travel.**

Most race tracks are fairly smooth, all things considered. They don't have speed bumps, curbs, off camber driveways, pot holes, sink holes...... I caution against using the coil-over as a pure travel stop to help shed off impending doom.

Well Rob, I figure you're gonna have to have a bump stop somewhere in the system, and that will always consume part of the "free travel", be it on the damper shaft or mounted to the frame. Assuming it is a progressive stop, not instant. Agreed, the O-rings would make a poor bump stop!

RE Suspension has a good selection of shaft mounted bump stops:

http://store.resuspension.com/home.php?cat=328

You know, now that I think about it a little more, every German car I've owned (BMW, Porsche, Audi) also has the bump stops mounted on the damper shaft. I believe putting bump stops on the frame might be unique to American cars?

Gustave

Tincup
08-21-2015, 07:23 AM
Here's another basic question, boxing the chassis. Should it be completely boxed and cross bracing added, or do you want to leave "some" flex in it.

Dr G
08-21-2015, 08:53 AM
No, you never "want" flex. The less flex the better. The only thing that should stop you from reducing flex is that it is adding too much weight as part of the process. The bad thing about making trucks handle is that they have a high center of gravity. But the good thing about that is that there is a ton of room between the bottom of the cab/bed and the ground to build a very stiff frame, short of adding a cage. I vote yes, box everything. Look at No Limit frames for examples of how to build an intelligent frame, stiff but not just by throwing weight at it.

RobNoLimit
08-25-2015, 09:01 AM
Time teaches you lots of things. Back in the '80's we were boxing chassis end to end. (mostly 53-56 F100 and 55-59 chev) These were almost all 'ladder' style frames. This lesson took 6 or 7 years to learn. My own 56 chev p/u (camaro clip and ladder bars, BBC, Th400) started to crack at the joint areas for the crossmembers. - Now it may be true that I put my truck through harder paces than most, but there was still a problem looming. By this time I was in college, learning about harmonics, stress loads and vector forces..... It all made perfect sense. The Ladder style frames, especially the older ones that came with leafs and beam axles, were DESIGNED to flex. Bad roads, heavy loads and cost dynamics forced this. The ladder frame design is basically two dimensional - length - width, not much height. So, you can make it stiffer and stronger, but if you take out the rail flex, it will crack. Now a days, we box the front, from the firewall/front cab mount area, forward to the front core support, and the rear section, about three ft. from the rear shock crossmember forward over the frame kick, and up to the suspension link mounting area (4-link or 3-link). Then we work on creating an 'X' member in the center of the chassis.

bergers59
08-25-2015, 06:32 PM
Why is it that longer shocks are better? I've seen it in a few builds where the shocks are at least 10" and always wondered why.
Also, it's threads like these that keep me coming to this site for the past few years, so thank you.

Dr G
08-26-2015, 08:18 AM
Time teaches you lots of things. My own 56 chev p/u (camaro clip and ladder bars, BBC, Th400) started to crack at the joint areas for the crossmembers. - Now it may be true that I put my truck through harder paces than most, but there was still a problem looming. By this time I was in college, learning about harmonics, stress loads and vector forces..... It all made perfect sense. The Ladder style frames, especially the older ones that came with leafs and beam axles, were DESIGNED to flex. Well I cannot argue with your experience Rob. I guess the boxing creates stress risers at the cross members.

I do know that my current frame is as you suggest, stock with boxing up front and out back. And I hate it. It is so flexible. I guess that's why you sell custom frames right! Gustave

Tincup
08-28-2015, 07:47 AM
Basic question of the week, shock placement. I know on your Fatbar the shocks are placed outboard of the frame. Most other builders place them inboard, even the OEM places them inboard. On the chassis I have the shocks were mounted inboard, with one shock on either side of the rear, one angled forward, one angled back. What's the reasoning behind the different choices...?

72BBSwinger
08-28-2015, 11:35 AM
The forward and rearward placement is almost always on a truck and IMO is for better wrap control under towing conditions.

Bob in St. Louis
08-29-2015, 07:25 AM
This is a fantastic thread. So much great information.
Thanks to those of you who are sharing your knowledge.

RobNoLimit
08-31-2015, 11:00 AM
Basic question of the week, shock placement. I know on your Fatbar the shocks are placed outboard of the frame. Most other builders place them inboard, even the OEM places them inboard. On the chassis I have the shocks were mounted inboard, with one shock on either side of the rear, one angled forward, one angled back. What's the reasoning behind the different choices...?

Yes, the for/aft shock placement is for axle wrap and harmonics control. We place the shocks outboard for better ride control. Ford and GM are now doing this on their trucks. The closer the springs/shocks are to the center of the car/truck, the more it will tend to act like a 'teeter-totter' in the corners and over bumps. The farther outboard they are mare the shock more reactive and the vehicle more stable.

Tincup
08-31-2015, 12:28 PM
So Ideally, you want them mounted outboard of the frame, staggered front & rear....Like a Ford...

116721

RobNoLimit
09-01-2015, 05:27 AM
This is a leaf spring set up, so staggered shocks (without the coil spring) will help the natural spring wrap and oscillation. - But, these shocks are not carrying the weight (spring load) of the suspension. If you were to stagger the shocks on a four bar/coil over set up, the two sides would react differently. The coil-over in front would see a higher load, and slightly less travel, the rear coil-over would see a lower load, and slightly more travel. (realistically less than 3% difference) So to get the two sides even, you would need custom springs and valving for each side.
- No, Ford doesn't have a 'left' or 'right' shock. It's the big compromise. this gives them the best ride for the least $$$. Honestly, I would rather put the coil-overs in front of the axle, but that brings in a packaging problem, so, to get everything to fit, we put them on the back side. - Except for our Big-10 chassis, where they are chassis mounted and drivin with a push rod and rocker arm, on the front side.

Tincup
09-01-2015, 07:00 AM
So, that being said, if you were to stagger your shocks on a four bar setup, I would imaging the smaller the angle between the two shocks, the smaller the difference ( 1%-2%). The reason I'm asking is my rear ( Dana 60 ) already has the shock mounting brackets for a staggered setup welded on. I was thinking of using them, if they work out...

RobNoLimit
09-10-2015, 05:13 AM
This is from a current project we are building for an 89 C1500. With any air suspension the air bag (or air spring) will have a givin Ride Height range, a max open height, and a closed height. Some have internal bump stops, these do not. These bags are 4 1/4" closed, 8" to 9 1/2" RH, and 13" open. In full droop (lifted) the shock will be the limiter. At full compression (dropped) there will be a bump stop on the chassis that contacts the axle. At this point the bag will be at 4 5/8", and the shock will have another 1/2" of travel avail.
When we laid out this chassis, we started with the tire ht @ 28", so 14" to the axle center. The bottom of the rail under the cab is to be appx 5 1/2" @ RH. From the axle center, we star adding. 1 1/2" for the housing, 4 1/2" up travel of the rear axle, 1/2" bump stop. In total we need 14 + 1 1/2 + 4 1/2 + 1/2 = 20 1/2" from the ground to the bottom of the rail (over the top of the axle housing) at RH. So if the center of the frame under the cab is at 5 1/2" at RH, the rails need to rise 15" (bottom of the rails) from the cab area to the top of the kick over the axle.
The shock does loose some of it's dampening laid back like this, and that's part of the plan. In the 'Ride' zone, the shock has lost 18% of it's dampening force compared to being 1 to 1 with the axle travel. For trucks, that have a relatively high ratio of unsprung weight, this helps with the ride quality. We can tune in the rebound with the HQ series shocks. Have you ever thought "Hey. I need more compression dampening on the rear shock?" - No. Now, down at full drop, the shock looses even more (somewhat regressive). And since this is just a 'park', or 'cruise' stance, it's OK, and it will air up quicker without the heavy resistance.
_ Fire away.

Tincup
09-17-2015, 10:32 AM
Let's keep this thread going. The topic of the week, Sway bars, should I use splined or standard. What is the theory on splined sway bars, are they better? just for race cars? I only plan on hitting the Autocross once or twice a year, so primarily a street truck. So would standard sway bars be OK?, front & rear?, larger front than rear?, same size?

David Sloan
09-21-2015, 03:14 PM
I was really hoping this would keep going as I am at the point of picking bars for my car!
I want to be able to change the bar for tuning / an not sure how to pick the right size to start with.

RobNoLimit
09-22-2015, 05:42 AM
I'll get right to it. The main reason to go with a splined bar is tuning. The secondary reason is fitment. That one cuts both ways. A splined bar set up gives the builder the freedom to shape the arm to fit the chassis/tire/suspension. The price tag here is that the builder has to make it work. Splined arms come flat. - you get to shape them. When it comes to the size and shape of the bar/arms, you need to know the range of roll resistance that your after. For that you need to know the range of TRS (Total Roll Stiffness), and for that you need a whole list of chassis and suspension info. (not here, or just yet. Be prepared to buy some books and software for that stuff). So, for now, take a SWAG at it. (Silly Wild Ass Guess). When it comes to effective rates, the bar diameter, wall thickness (if not solid), bar length and arm length can be plotted with relative ease. 'Drift out' of the arms is a lot harder to calculate, so we don't use it much. Once the arms are fitted, you don't change them, so for comparative tuning, this becomes a constant. Just know that the more 'drift out' you build into the bar, the less effective the bar really is.
For most builds, a formed bar is fine. But here is the catch. Can you get one for your build? A Fox body Mustang (example only) uses a formed bar, and there is plenty of TESTED aftermarket support for them. So you can buy different formed bars for more performance tuning. - Now, take a minute to list all of the companies that have done actual track testing on sway bars for your style of truck build, and, using the suspension design your choosing? OK, short list, see where I'm going? What size bar will work for you? Sad as it is, many chassis and suspension builders are churning out product that they have NEVER driven, or worse, NO ONE has ever driven. Just a SWAG from the drawing board straight to your project. Kinda sad and scary. If your using 63-72 or later C10 stuff, there are a few. No Limit, RideTech and Hotchkis. You can guess at sizes based on these examples, but consider arm length as well. Longer arms = less bar.

Here are some picts. Both fronts are No Limit Wide Ride IFS units. One with a splined bar and one formed. The formed bar is 1 1/8" solid. The splined bar is 1 1/4" x ,188" wall. These net close to the same. They have the same tire clearance, and mount in the same locations. One can be tuned later, and one can't. - unless you have another formed bar to change to (like a Fox body would). So, are you the kind of guy that would change bars at a Good-Guys event or SCCA track day? Or will you tune your street ride to get the best ride for everyday use? If the answer is an honest yes, put in a splined bar. If not, go with a formed bar.

Tincup
09-22-2015, 06:07 PM
Awesome explanation, thanks....

David Sloan
09-25-2015, 12:36 PM
I guess I need to do some reading so that I know were to start as far as size goes. I will want to be able to tune it for different tracks / auto cross , maybe open road racing
Thanks for the info

RobNoLimit
09-26-2015, 06:24 AM
The current trend is big tires. But, if the wheel/tire combo interferes with the suspension/chassis, in such a way that it limits the degrees of steering available than the big tire may not be a win. You need to have 28* of steering, or more.

One of my thought trends lately is all about tire size vs. weight. If you have great suspension, and you can keep the tires planted through the corner, your thoughts soon move to the size of the contact patch. The tires contact patch is all you've got to transfer the forces to the ground. Those forces are, Torque (engine HP & gearing) Braking, and Lateral acceleration (cornering forces, in 'G'). Thinking about them separately to make it clearer, you may think like this: Adding Torque helps in acceleration,- and we are accelerating the mass (weight) of the car, but only if the tires can plant it. Big ABS brakes will help braking, again, we are slowing down the total mass of the car, but only as fast as the tires can hold. And Lateral G, which at some point in the formula, when you balance suspension and aero, comes down to contact patch grip vs. mass. The constants in all three concepts are tire contact patch, and mass. And while everyone is trying to stuff bigger tires under the car and build more HP and buy monster brakes, mass is not talked about much. - food for thought.

Tincup
12-29-2015, 12:44 PM
Time to revive this thread. Let's discuss engine placement, the further back the better?

Austin97C1500
12-29-2015, 05:40 PM
Wow! This is alot of great information. My father and I are doing a 97 C1500 build that will get an engine swap soon. Before we begin we are sorting out suspension. Leaning towards a 3 link out back and between Rob and Ron on the forums and sharing tons of information I feel like I'm getting a better education than the one I paid for!

RobNoLimit
01-04-2016, 06:41 AM
Sorry guys, I missed this in all of the Holiday hustle.

As far as engine placement goes, look at it this way. Weight can be positioned over the four tires (the rectangle shaped 'platform') in only three ways. We might call them X, Y, and Z, but I will say Front/Rear, Side/Side, and Up/Down. Lets focus on ride quality and general handling (not drag racing) and say that the goal, with the driver included, is to get close to 50/50 on the Front/rear and Side/Side, and to get the Up/Down as low as reasonable. While your working on that, trying to keep the total weight down. I.E. - don't just add weight to get the Side/Side to 50%, move weight or cut weight. So, the basic answer to the motor question is, down and back.

RobNoLimit
01-04-2016, 07:49 AM
OK, you opened the door. This is something I have wanted to discuss for a while. I generally put 'weight' into three categories. 1) Sprung weight. All of the weight that is help 'up' with, or moves to compress, the springs. This is most of it. 2) Un-Sprung Weight. This is all of the weight that is NOT held up by the springs. 3) Rotating Weight. Some of this is "Sprung" and some "Un-Sprung". For now, lets just look at "Sprung Weight" - SW - and "Un-Sprung Weight" - USW. While you think about total weight, and 'lightening' the car/truck for performance, thinking about USW would be smarter.

When the suspension reacts to a change in the road/load/corner... there are two main goals, 1) to keep the contact patch of the tire on the ground as much as possible 2) to get the vehicle/suspension back to it's static RH as quickly - and smoothly - as possible. So, the 'load' compresses the spring with a #force, and the spring wants to go back to it's normal position with an = force. BUT, the ghost in the room is USW. Imagine you are driving down a road and you hit a 2x4 with the left front tire. 1) the RF suspension compresses some, loading the spring more. 2) that additional spring load caused the RF of the truck to 'lift' up some. 3) ** some of the energy from the bump hit the tire, and caused that mass to change direction ** OK, Laws of Physics. .....A force in motion will remain in motion until some other force acts upon it..... So, for a moment, the direction of the wheel/tire (USW) was changed from 'forward', to 'up'. Then the spring/shock have to use some force to control and change that back to 'down' and then 'forward'. The more the wheel/tire (and the rest of the USW) weight, the harder it is for the spring/shock to control. Also, and another negative, is that the higher the percentage of USW, the more the USW can move the rest of the car/truck - SW - around. - a bumpy ride.

This is why there is a term "rides like a Caddy". Cadillacs are really heavy, but, because of all of the SW, the %percentage of USW is relatively low. So, when a Caddy hits a 2x4, the USW doesn't have as much leverage over the SW. But, not too many people ever said "handles like a Caddy" - (current CTS-V owners excepted)

To calculate USW, lets say of the RF of a C10 (OK, I'm going to take LOT of assumptions here) you would need to weight some components separately, and some half supported. I'll go through the list.
Wheel and tire = 70 lbs.
Rotor, bearings, studs, seal = 18 lbs
Caliper, pads, hardware = 12 lbs
Spindle, hardware = 19 lbs
Now, we have to look at what part of the next group is actually moving with the suspension
LCA, - support the pivot end and weigh the ball joint end = 8 lbs
UCA - support the pivot end and weigh the ball joint end = 6 lbs
TRE - support the inner TRE and weigh the tie rod and outer TRE = 4 lbs
Sway bar - support the middle bar and weight the 'arm' and end links - this will weigh both sides, use 1/2 of the weight per side. = 4 lbs
Spring/shock - for now, use 1/2 of the total weight = 5 lbs (coil-over)
So, for the average guess C10 we have 146 lbs of USW. - (this hurts to say) So, if you have the average C10, at 3500 lbs and it has 56% front weight there is 1960 lbs on the front. Or, 980 per side. Now, at first you may think, 980 vs. 146 isn't so bad, but that's not how it is. 980 is the Total weight. To get a % of SW vs. USW you need to take the total weight - 980 and subtract the USW - 146 to get the SW of 834 lbs. now you have a comparison of 146/834, or 17.5%. Now, as a rule of thumb 15% is the good/bad break, and 12% is the good/great line.

So, keep this in mind. Light weight wheels/tires/suspension/brakes are a big help. Also, if you are looking to really compete in some track events, 'truck' based suspension is just too heavy. Now, if you cut some USW, and then you lighten up the front, and move the motor back and change the ft/rr %, then you also reduce the front SW, and the % goes back up. It's a fight. When you get down to 800 total on the RF, you will need to be down to about 85 lbs USW to get a 12% ratio.

This little understood ratio of SW vs. USW is why shock valving is such a big topic in the USCA and Auto-X circles right now. Cars are getting lighter, and the % of USW is going up, making it harder for the shocks to control the forces in motion.

Here is a sketch to help imagine all that is moving around. Have a Happy and great Handling New Years!

RobNoLimit
01-05-2016, 06:19 AM
Last night I was thinking about this some more, and I thought of a more relatable example. On this thread we are all at least interested in trucks, so it's safe to say we've all driven at least one. And, we all know the 'bouncy' feeling from the rear. This is mostly due to two things. 1) Too much spring rate. Trucks are for work, and the have to carry a load, so the springs are set to be 'happy' at appx 60% of total load capacity. At full cap. they are max'ed out, and when the truck is empty, they are 'under-loaded'. (too stiff) and 2). a high % of Un-Sprung weight.

Back to our theoretical C10. rear weight appx 1400 lbs (total weight)
Now for the Un-Sprung weight.
Rear axle, gears, brakes = 265 lbs
Wheels and tires , 2, = 140 lbs
Half of the trailing arms = 35 lbs
Half of the coil springs, shocks = 14 lbs
Half of the driveshaft = 16 lbs
Half of the panhard rod, = 6 lbs
Total unsprung weight = 476 lb

So if the total rear weight is 1400 and the Un-Sprung is 476, that leaves only 924 lbs of Sprung weight. Do a little math and you get an Un-Sprung percentage of 51% !!!!! So think about it, when the trucks back tire hits a bump (one side) and 238 of mass is now moving 'up', it's easier to 'lift' the back of the truck, 462 lbs, than it is to compress the spring.

bovey
01-05-2016, 07:20 AM
Last night I was thinking about this some more, and I thought of a more relatable example. On this thread we are all at least interested in trucks, so it's safe to say we've all driven at least one. And, we all know the 'bouncy' feeling from the rear. This is mostly due to two things. 1) Too much spring rate. Trucks are for work, and the have to carry a load, so the springs are set to be 'happy' at appx 60% of total load capacity. At full cap. they are max'ed out, and when the truck is empty, they are 'under-loaded'. (too stiff) and 2). a high % of Un-Sprung weight.

Back to our theoretical C10. rear weight appx 1400 lbs (total weight)
Now for the Un-Sprung weight.
Rear axle, gears, brakes = 265 lbs
Wheels and tires , 2, = 140 lbs
Half of the trailing arms = 35 lbs
Half of the coil springs, shocks = 14 lbs
Half of the driveshaft = 16 lbs
Half of the panhard rod, = 6 lbs
Total unsprung weight = 476 lb

So if the total rear weight is 1400 and the Un-Sprung is 476, that leaves only 924 lbs of Sprung weight. Do a little math and you get an Un-Sprung percentage of 51% !!!!! So think about it, when the trucks back tire hits a bump (one side) and 238 of mass is now moving 'up', it's easier to 'lift' the back of the truck, 462 lbs, than it is to compress the spring.

This is great information. The number times I have people ask me about how to deal with the "light" rear of a truck is amazing. People refuse to believe that the lightness is due to spring rate, not physical weight.

I also want to dig up some info I have in a book at home that I believe would be an interesting add to this thread, it talks about sprung vs unsprung weight vs. rotational weight and how they are not created equal when making a vehicle lighter. Rob, your information about USW being 12% is neat, I did not know that. Thanks for the great intel.

Rod
01-05-2016, 10:51 AM
great stuff! dig the topics and tuning strategy, so i pose extra questions...How much SW must you shave off to equivocate it to shaving off 1 pound of USW or vice versa, at what poundage number do you start to feel the effects? 200, 300 pounds...

and what does it take to over come SW poundage

what I used to see was most guys dropped a 100 pounds off the car and added power to there ride to help, but the next level is now drop 300-400 pounds and add power

CA B4C
01-05-2016, 11:32 AM
When can I sign up for your suspension class?

RobNoLimit
01-05-2016, 01:16 PM
great stuff! dig the topics and tuning strategy, so i pose extra questions...How much SW must you shave off to equivocate it to shaving off 1 pound of USW or vice versa, at what poundage number do you start to feel the effects? 200, 300 pounds...

and what does it take to over come SW poundage

what I used to see was most guys dropped a 100 pounds off the car and added power to there ride to help, but the next level is now drop 300-400 pounds and add power

As more and more guys cut weight, and for some that have - in the 300 - 400 range, shock tuning will get more and more difficult due to the USW %. Most weight is being cut from the body/chassis/interior. All Sprung Weight. This may help in a drag race, but not so much around corners an really not so much on un-even surfaces.

Put the weight into three groups and cut accordingly. - OK four (I decided to cut one in two)
1) Rotating and Un-Sprung. This is the worst. All of this weight moves to upset the car, and all of it has to accelerate and decelerate. Wheels, tires, hubs, rotors, axles, gears...... This is one of the hardest areas to cut weight, and it can get expensive, but the pay-offs are big.
2) Un-Sprung weight. 2nd worst and equally hard to cut. With the rotating section removed, there isn't a lot left. Spindles, axle housing, calipers, control arms, shocks and springs.... ever wonder why Afco makes "Lightweight" coil springs? Again, this is a tough place to cut.
3) Rotating and Sprung. Get you wallet out for this one. balancer, crank, rods, pistons, flywheel, clutch, driveshaft. This won't be big in poundage, but it will pay off in performance - acceleration.
4) Sprung weight. the easy one. This is everything else. Body, interior, chassis....

Before you dismiss some of those as "not enough to worry about", think about the bracket racers that disconnect the alternator to win a race.
I try to think of the USW in %, not lbs. It helps me focus on the weight I should be concerned about most.

Twentyover
01-06-2016, 03:10 AM
So if the total rear weight is 1400 and the Un-Sprung is 476, that leaves only 924 lbs of Sprung weight. Do a little math and you get an Un-Sprung percentage of 51% !!!!! So think about it, when the trucks back tire hits a bump (one side) and 238 of mass is now moving 'up', it's easier to 'lift' the back of the truck, 462 lbs, than it is to compress the spring.

Think you need to try the math again 476/1400, not 476/924, for closer to 35% unsprung weight, but the rest is good

RobNoLimit
01-06-2016, 06:36 AM
Well there is more than one way to skin a cat. That's what I heard anyway. When I compare Un-Sprung %, I do this based on the amount of Sprung weight above that corner. - Not the total weight (which would include the Un-Sprung weight). If you put a car on scales, and separate out the weight on the rear axle (LR and RR weights) this includes the Un-Sprung and Sprung weights to give you the total. But what I am interested in is the comparison, or relationship between the two, Sprung vs. Un-Sprung. in the example, 1400lbs was the total weight, including both SW and USW, so, I subtracted my estimated USW (476) from the total to get an estimated SW of 924 lbs. The relationship that I am interested in is the % match up (as a comparison and tuning number to scale with) between those two.
I have read of some using USW as it relates to TW but this doesn't make mush sense to me when it comes to shock and spring tuning. As it is the shock and spring that work between these two masses/forces. (USW vs. SW) - That's why I did it that way. - your results may vary.

2ndroundko
01-06-2016, 01:50 PM
I recently inquired about a rear set up for my truck and got some great feedback. this last bit of information explained why those things would be of great benefit. as usual good stuff Rob.

S Griffin
01-09-2016, 03:41 PM
Great read Rob. Thanks for sharing your vast amount of knowledge!

mitch_04
02-09-2016, 11:59 PM
I love this thread and have a question. I am designing a full frame/suspension for my 85 C10 and was curious about frame width. Is there a benefit to having a wider frame vs a narrower frame? Or is it best to follow stock width?

Rebeca_Lynn
02-10-2016, 03:36 AM
Rob,

Can you explain the same thing for independent suspension set up on the rear? I have been looking at using a C6 based suspension and drivetrain. I know this will save some weight on the SW and pending on the parts it may over all, by spreading the weight of the motor and transaxle or I should say help to balance the F/R weight, along with possibly lowering the height of the weight as well.

Dr G
02-10-2016, 09:38 AM
I love this thread and have a question. I am designing a full frame/suspension for my 85 C10 and was curious about frame width. Is there a benefit to having a wider frame vs a narrower frame? Or is it best to follow stock width?Are you asking about the width of the frame rails? Or the width of the frame from rail-to-rail? Gustave

mitch_04
02-10-2016, 10:15 PM
Should have specified, the distance between frame rails. Is a wider frame or a narrower frame (not frame rail) preferred, and why?

RobNoLimit
02-11-2016, 06:26 AM
I love this thread and have a question. I am designing a full frame/suspension for my 85 C10 and was curious about frame width. Is there a benefit to having a wider frame vs a narrower frame? Or is it best to follow stock width?

Good question. Here is a simple engineering test that we can all understand and remember. I won't drag in all of the math, just an easy demonstration. Think of a chassis as a link between the front and rear suspension. Most forces will be in one of two main areas. 1) flex in the middle - support the chassis on both ends and apply force in the center. Any direction, up, down, sideways, ... and 2) Grab the chassis at each end and try to twist it. Got an image of that? great. Now, imagine the chassis as a link, or a tube for our discussion. Start with a 1 1/4" solid round bar, 10 feet long. Can you bend it? and/or twist it? I bet you could. Now, compare this to a 5" diameter tube with .120" wall thickness, 10 feet long. (Just so you know, these two links have appx the same weight, within 4%, so there is appx the same amount of metal in each). Can you bend it? a little, can you twist it? Not so much. Give that some thought.

The general rule is that 'larger' the dimensions you have - against the forces applied, the better off you will be. A 'wider' chassis resists 'side' forces more. A 'taller' chassis resists 'up' and 'down' forces more. A more 3-dimensional chassis resists 'twist' forces more. OK, this is a really over simplified look, but the concept is true. Yes, X-members, crossmembers, material thickness, gusseting....... all can help, and the overall design can be improved, but as to general width, there you go.

RobNoLimit
02-11-2016, 06:36 AM
Rob,

Can you explain the same thing for independent suspension set up on the rear? I have been looking at using a C6 based suspension and drivetrain. I know this will save some weight on the SW and pending on the parts it may over all, by spreading the weight of the motor and transaxle or I should say help to balance the F/R weight, along with possibly lowering the height of the weight as well.

Disclaimer: I have very little knowledge with IRS suspensions - but I am rapidly learning. ** OK, so yes. The C6 IRS concept is a good one. The actual transmission is basically moved back to the rear axle, or just in front of it, for better weight balance. And, with an IRS, the differential and it's housing go from being 'un-sprung' weight, moving with the tires, to being 'sprung' weight, moving with the chassis. With my current Cobra project I have found the IRS to be lighter in total weight that a 9" would have been, with a lot less USW. So, over all, it's a win/win/win. Less USW, less total weight, and better weight balance.

There may be a negative, and that's the width WMS/WMS (Wheel Mount Surface) The C6 IRS is like 64" wide. (don't quote me it was a guess) For F-100's we want about 60", and for C10's around 62". For a later (67 on up) you can make tis up with wheel offset, but for narrower builds, it's custom arms and half-shafts, and some other things. So measure it out first.

Rebeca_Lynn
02-11-2016, 05:19 PM
Thanks Rob,

I guess it is time for my husband, son and me to sitdown and start doing so design work with Autocad and Solidworks. Get a couple basic ideas laid out and try to figure it out from there.

- - - Updated - - -

Thanks Rob,

I guess it is time for my husband, son and me to sitdown and start doing so design work with Autocad and Solidworks. Get a couple basic ideas laid out and try to figure it out from there.

bmbrzmn101
02-11-2016, 07:54 PM
Well where have I been that I missed this thread entirely? Great info here Rob, and thanks for you and others sharing not only the theory of the design but the process to start the basic design. . Ok back to reading......

Chris

Dr G
02-12-2016, 04:02 PM
The general rule is that 'larger' the dimensions you have - against the forces applied, the better off you will be. A 'wider' chassis resists 'side' forces more. A 'taller' chassis resists 'up' and 'down' forces more. A more 3-dimensional chassis resists 'twist' forces more. OK, this is a really over simplified look, but the concept is true. Yes, X-members, crossmembers, material thickness, gusseting....... all can help, and the overall design can be improved, but as to general width, there you go.
Having given this subject a lot of thought over the years, there is one more mode of frame deflection besides bending and torsion. I call it "shear" for lack of a better name. This would be where the left frame member moves forward while the right frame member moves backwards (or visa versa).

I find it interesting to look at early 60's Impalas on the Chassis Cam during Barrett Jackson auctions. They have what is termed an X-frame. Seen here:

https://static1.pt-content.com/images/pt/2016/02/DSCF0685M-1.jpg

Such a frame would be good at resisting shear forces, ok at resisting bending forces and horrible at resisting torsional (twisting) forces. And since shear deflection is not as likely as bending and torsion, I would not really want an "X-frame" under my F100.

The best way to stiffen up a car or truck is to install a well thought out roll cage. With a car it is about the only thing you can do. But with trucks you can do a lot more to stiffen the frame without resorting to a cage. There is a lot of room under the floor and bed of a truck, allowing for a tall frame, which as Rob points out is a good way to stiffen said frame in bending and torsion. I reckon on my 1956 F100 there is a good 10-11 vertical inches available between the bottom of the cab and the lowest part of the truck. Hence perhaps the No Limit Big-10 frame (10 inches tall).

https://static1.pt-content.com/images/pt/2016/02/138216427jpg-1.png

Gustave

kingcrunch
02-13-2016, 04:37 AM
Not aiming to be the smart-ass here but i think the important difference between the Big-10 chassis and a normal truck frame is the X-shaped structure in the center, that links all of the points that have some kind of force transmitted into them to eachother.
Without that, even an 11" tall lader type frame will twist like a fish...

I want to build a bolt-in X-structure like that for my projects frame.

For cars there's a lot more you can do than a roll cage (increasing the number of pinch welds, stitch-welding frame structures, adding reinforcement panels to link structures together, etc.)

Dr G
02-13-2016, 10:03 AM
Not aiming to be the smart-ass here but i think the important difference between the Big-10 chassis and a normal truck frame is the X-shaped structure in the center, that links all of the points that have some kind of force transmitted into them to eachother.
Without that, even an 11" tall lader type frame will twist like a fish...

I want to build a bolt-in X-structure like that for my projects frame.

For cars there's a lot more you can do than a roll cage (increasing the number of pinch welds, stitch-welding frame structures, adding reinforcement panels to link structures together, etc.)

An X-frame inside a wider rectangular section (Big-10) is different than an X-frame on it's own (like the Impala I showed). Generally you want to load tubes (or frame sections) in tension or compression, not in bending, in order to get the biggest increase in torsional stiffness. Also, I hope that I did not convey the impression that a truck can be stiffer than a car. With a truck the body panels do nothing for you in terms of stiffness. In a car, the existence of a roof make it stiffer than a truck, with or without a roll cage. But if you use the space available to you underneath a truck (which a car cannot do) then you can definitely improve stiffness a lot. Rob's Big-10 frame is the only one on the market that takes advantage of this possiblity.

In a previous life a was pretty into BMW M3's (E30 and E46) and I am aware that you can seam weld an entire unibody. But that is going to be an incremental thing (it's easy, cheap, does not add weight, so why not seam weld the body?). However, the biggest improvement in bending and torsional rigidity for a car will come from adding a roll cage.

As Rob mentioned, the ideal for torsional rigidity is a cylindrical tube (we're both engineers so this was taught us in college). Next up would be a square (or rectangular) tube. A truck frame can be thought of as a rectangular tube. At the risk of getting "wonky" here's a formula for the polar moment of inertia for a rectangular hollow section rectangular tube:

https://static1.pt-content.com/images/pt/2016/02/Screen20Shot202016021320at209493220AM-1.png

The polar moment of inertia dictates how stiff a tube will be in torsion about it's axis. If you look at the formula, you can see that the two relevant parameters are the height and width of the rectangular tube. Thus by analogy, for a truck frame, if you make it wider, taller, or both, you will make it stiffer. That is the point I was trying to make.

And for bending, making a truck frame taller is also a big improvement. Conclusion: if one is designing and building a truck frame with performance intentions, then if you do not make it as tall as possible, you are leaving meat on the table (so to speak).

Gustave

mitch_04
02-20-2016, 11:58 PM
Alright, so I have started to draw out my frame design. Some of my roadblocks thus far are...
1. How do you know when to narrow the front to clear the tires, and how far?
2. How close can the frame be to the tires in the rear without worrying about rubbing when one side is fully compressed/extended?

I am in Kuwait, a few thousand miles from my spindles and such so I am not able to get measurements to draw them out. If anyone has the essential measurements for an 85 C10 drop Spindle I would really appreciate it. I have suspension Analyzer and would like to draw something up before I go home.

rustomatic
02-21-2016, 08:30 PM
This is a great thread, and I'm not even building a truck. For clarity on what the guys are saying above about a "tall" frame, research the design of a C4 Corvette's frame. It's very tall, well through the front and rear suspension mounting points. (There's also a safety thing here, in that you sit inside of it, kind of like a tub or a coffin.) Then, when it's not so tall in the front, it gets fat . . .

So apparently, in truck (or car) frames, gymnastics, and boat building, we must always think of beam . . .

Dr G
03-26-2016, 10:57 AM
I was flipping through my archives and stumbled upon this article regarding a race car from the British Touring Car series back in the late 90's. This was a time during which great strides were made in how to use a roll cage to stiffen a vehicle in torsion. Before this time folks just thought of a roll cage in terms of crash protection. But the BTCC and World Touring guys in the 90's latched on to the idea that all these tubes, if properly placed, could make huge improvements in torsional rigidity. And that this in turn improves suspension performance. Just like there was a time when race car guys did not realize the benefit of wider tires, there was also a much longer period when they did not realize the importance of a rigid chassis in terms of getting a vehicle to handle. Automakers have likewise discovered that a stiff chassis is crucial to improving the all important NVH (noise-vibration-harshness) factor in passenger cars and trucks.

The article mentions the "section" of a car chassis relative to an F1 chassis. This bears directly on the statement I made that if you're building a pro touring truck frame, you should make it as wide and tall as possible. This increases its section (the size of a cross-section). A truck frame can be thought of as nothing more than a 'squat' roll cage or space frame.

See below if interested:

https://static1.pt-content.com/images/pt/2016/03/section-1.png

Gustave

Tincup
04-07-2016, 09:42 AM
Let's discuss pinion angle. I was kind of hoping to set the engine at zero degrees ( parallel to ground ) what should the pinion be set at? should it also be at zero degrees? The only problem is that they will almost be in perfect alignment ( no angle ) so no rotation of the needle bearings. Any help would be appreciated.

125718

RobNoLimit
04-08-2016, 05:42 AM
Well, having the crank parallel to the ground may be a nice thought, bu not too realistic. - It is do-able, but may not be the best bet - Most carb intakes have 2* to 4* of slope built into them, based on the OE settings, the carb was level, and the crank was at a slope. (down in the back) Even most EFI intakes are designed on the same idea. So to start with the eng and trans, once mounted, will probably lean back 2 or 3 degrees. BTW, oil pans, trans pans and headers are all built with this in mind. Having set the crank angle, start by setting the pinion parallel to the crank. Next, it's time to add in for what I call the 'pinion climb'. Under acceleration (and even a steady 60 mph is still considered accelerating against all of the drag forces against the car) there will be forces applied to the axle housing. The housing will want to rotate the opposite direction of the tire, and the pinion will want to rotate 'up' (if you are going forward). The type of suspension, tire compound, and engine torque will determined how far the pinion will be able to rotate. You want to counter act this, so that the pinion is parallel to the crank under normal load (70 mph freeway, where you don't want any vibrations).

As a general approach, I have this rule for pinion corrections. OE leafs -3*, Aftermarket leafs -2.5*, OE link -2*, aftermarket link w/poly ends -1.5*, Torque arms, trailing arms and aftermarket links with rod ends - 1*, competition only aggressive 3 and 4 links, - .5*.
This would be the degrees to push the front of the pinion 'down' from being parallel to the crank. The torque and suspension flex will then wind the pinion back up to parallel under load.

** This is NOT the way to do it for 4x4, crawlers, and dirt cars, they have there own rules.

** Way back in the day with the Nissan GTP cars, we set the pinion angle on the dyno, to get max torque (min power loss) at the typical corner exit through peak pull. We would spend hours doing it to get a 3 or 4 ft/lb advantage. That's how you win championships. It all adds up.

Tincup
04-08-2016, 11:51 AM
As usual, Thanks Rob.
So if I understand you correctly, if I set the intake at 0* the crank will probably be -2* to -3* down. And with the crank at -2* to -3* down , set the pinion at +2* to +3* up to make them parallel, minus the -1.5* down for my Fatbar suspension, equals +0.5* to +1.5* on the pinion. Correct?

Tincup
04-10-2016, 02:17 PM
How about side to side? My pinion is approx. 1" offset to the passengers side. Should the engine be offset 1" to compensate?

mitch_04
11-12-2016, 08:42 AM
I asked Ron Sutton the same question once and he recommended moving the engine to help balance out the weight of the driver. 1" shift of a ~800lb drivetrain should help decently well plus you align everything. However, that's all based on if you have the room too!