suspension geometry relocation

[trackrat79]

I downloaded the demo of suspension anylizer and am playing around with moving my suspension geometry around. What are some numbers I should look for in say caster, camber gains. Initial caster, camber. Toe in initial and gains. Roll center hight, anit dive %

I am confused as to what aproach is better. MY friend just purchased a c-4 corvette suspension package to put in his truck and the upper and lower control arm pivots are parrallel to each other and to the frame, but then theres nascar and other forms of racing that use lower and upper arms that are at completly different oriantations too each other. Is there one design type that is a clearly superior design that I should try and emulate.

[astroracer]

If you run the C4 demo those are good enough numbers that, if you can get close, I would call it good. If you can improve them that is even better.
Anti-Dive is generally designed into a suspension to "overcome" the inability of soft springs and shocks to control vehicle attitude under hard braking and acceleration. This is especially true for the OEM, mass produced, cushy-ride vehicles. Taking out the anti-dive, as it sounds like your friends C4 kit has done, isn't all bad as long as you can do something else to control attitude. Stiffer springs and shocks are a couple of ways to do that. You can put the anti-dive back in if you use the points from your PT Program. This should involve rotating the upper arm a bit around the ball stud point.
As far as one "perfect" design to emulate? Nope... Every vehicle is different. Every vehicle will be driven "differently". Every suspension design out there is a compromise in way or another.
Mark

[trackrat79]

I realize there are compramises. but I was hoping that there was a school of thaught or a often used design style that I could kind of look to as a guide.

I started with the 2002 corvette suspension model and manipulated the numbers from there. I am leaning towards track day use setting more than every day driving comfort. I want to get the best performance I can and just deal with a rough ride on the street. I maybe put 2000 miles on the truck in a year so I can deal with a harsh ride quality.

I cant find a way to export my specs so I will try and list the ones I think are important.

Role center HT 1.8, Toe in 0, Toe in gain -.15 Caster 3.9, Caster trail in .48, Caster gain .01, Camber -1.5, Camber gain -.58, King pin angle 10.48, Scrub radius 1.73, Spindel angle 8.98, Anti dive .0%, Front natural frequency 1.93

If theres other measurements that I can list to help you diagnose my design let me know.

[astroracer]

What amount of dive and roll are you using to run your calcs? I usually run them at 1" dive and 2 or 3 degrees of roll.
I can see a couple of things that I don't like in your numbers. The Toe looks like you are getting some bump "out". You want to optimize the suspension for as little "bump" as possible. Any amount of bump steer, whether in or out will make the car twitchy in high speed corners and during braking. -.15 is excessive and it will be a problem.
Have you moved the upper and lower control arm points? Doing this, without revising the steering rack inner points, will create bump steer issues. The BEST advice I can give you here is, work with the Corvette rack and optimize the upper and lower control arms around those inner points. Don't just randomly change things and expect good numbers. It isn't gonna happen. The suspension for my Bad Ast Project has 0.01 bump, total, over 3" of travel... That is what you want to shoot for. I started with a Corvette rack and built out from there. The inner pivot points of the rack determine where the upper and lower control arm inner pivots need to be, not vice-versa.
Running a Camber of -1.5 degrees on the street is going to do nothing but wear out the inside of your front tires. 0.0 to -0.5 would be the most you should ever need. Especially with wide tires. Check the camber settings for the C5 suspension. There is no reason to deviate from those numbers. The stock Corvette points will work very well with your truck and randomly moving points around is not going to "improve" anything... What you have to realize is, the whole suspension works as a system and, when you start moving a few points around, it throws everything else out the window...
As far as "emulating" a suspension design? The Corvette is about as good as it gets... Why screw it up?
Mark

[trackrat79]

I have no previouse experiance with this. I just started moving things around based on what I have learned with my 1/10 and 1/8 scale r/c cars. And we run upwords of 3 deg camber and 4 deg caster. and any were from 0to 2 degrees toe out.

Also I have track width that I am trying to meet so it was necesary to pull the pivots inboard. As it stand my tires stick outside the body almost 2 in per side. And i cant go any deaper on the rim back spacing because of spindal (mainly the steering arm) and ball joint clearances. The big camber numer is in part because of the tire I am planning to run. I am running a 11 in tread 27 tall on a 15x10 rim, so I have lots of sidewall flex compared to a big rim low profile tire combo so I am trying to optimize my contact patch under cornering load. Also I am trying to use my stock suspension pieces( upper and lower arms) so useing the corvette points wont work. Theres a 7 in differance between the upper and lower arm lengths. I dont have the mony to buy a corvette suspension to drop in place of the old stuff like my friend did. What I do have is time and ability for this type of work.

I will keep messing with it. I just got the program yesterday. Thanks for your input.

[astroracer]

I'm not trying to piss you off so please don't take my posts any way other then informative or information gathering.
There are a lot of things to think about when redesigning an existing suspension, especially when you are new to it. Keep in mind your truck is NOT an R/C car. You have to get in it and drive it and you would not have a good time driving your R/C car with that suspension set-up.
If anyone is to evaluate your design we HAVE to know what has been done to set it up. Right now your design doesn't work, plain and simple. Too much bump and too much camber. That is why I keep telling you to "emulate" the Corvette design. Which you can't do because, if I understand your last post correctly, you will be using the stock truck suspension.
Let me ask a few more questions:
1). You are using the stock truck suspension and moving things around to try to emulate Corvette performance?
2). You are you going to use the stock truck spindles and brakes ?
3). Is this a road race truck or a street truck? Where will it see 90% of it's "road" time? Be honest with your answer...
4). When you started plugging in points did you measure where your truck points were at? Or did you start with the Corvette points?
5). What is the stock track width?
6). What track width do you need for tire clearance?

Starting with the Corvette points will not work. Plain and simple. All the Corvette stuff does is muddy the water. You really need to measure your truck because that is what you will be using. Measure the points as best you can and input them into the PT program.
Try to find this book:
How To Make Your Car Handle. By Fred Puhn. Published by HP Books
It has all of the information you need and he goes through how to measure a stock suspension.
Your truck has a recirc ball steering box and, unless you plan to swap to a rack, you will need to re-engineer the steering to get rid of bump steer after you narrow the track width.
If you plan to switch over to a rack you need to get your stock arms measured and input into the program so, when you get the track width correct, you can develope the inner pivot points for a custom steering rack.
Inputting your stock points and working from there is the only way you will get your stock truck suspension to work like you want it to.
Do you have the front wheels and tires you plan to use? You may want to check turning radii and clearance to your stock arms if you haven't already.
And set your camber number back to 0.

[trackrat79]

No,no I am not at all upset. I value your info. I have enjoyed are previouse disusions and was hoping you would have some ideas.

Yes I am tring to move the stock moutning locations to try and get the best performance out of it. As far as usage. until the truck is fully completed I admit that it will only see street duty. But I live less than half an hour from Sears point raceway, and a few other road coarse's are within 2 hours driving so it will definatly become an allmost dedicated race truck when completed.

The idea right now is to stay with the truck spindals, The brakes I have uppgraded already but I hope to get even better stuff later on. I have toyed with the idea of useing a spindal from something else but I have limited knowledge of what would be interchangable with my truck .

I started with the corvette model just to see what its numbers were. Then I measured the part dimensions from my front suspension and started pluging them in. With the radical differance in arm length from top to bottom I cant seem to dial out the big camber gain. I fixed the toe gain it is now at 0.0, caster gain is -.08 but my camber gain is still -.84. the anti dive is at -43.3% the stock mounting had 0 anti dive. I also reset the initial camber to 0

Question, what is considered track width. is it the outer edges of the tires or the outer edges of the hub face. NOt sure. Fender lip to fender lip is 80in and the sidewall of the tires are out about 1.5 in per side right now. The rims are a 4in backspacing. So i think my track is (68-70 in )as it sits now.

I do plan to change to a rack since I cant find a steering box to fit my wants that will bolt up. So I figure if I would have to swap to a car box and make mounts for that I mite as well just convert to a rack.

Another possablility is to graft on a mid eighties monte carlo front end or something similar if that would be better. I can get those for pennies.

Any way thanks again for all your input.

[Marcus SC&C]

Okay I`m gonna take a little different tack here. C5 geometry is great...for a C5. 51/49 weight distribution,wide,super low,lightweight, aluminum engine behind the front lower ball joint centerline and transaxle in the back. They run VERY MILD camber gain and they don`t need much because they have almost no body roll and very little weight transfer under hard braking. Your truck`s needs are radically different. I`d would suggest starting by plotting all the factory pickup points you`ve got now and save that as a baseline. Now keep in mind the pickup points you intend to keep such as upper and lower ball joint and outter tie rod end pickups and start playing with the others. I`d be shooting for an RC about 2.5"-3.5" high (for a truck) with as little lateral migration as possible. At 1" dive and 2* roll no more than 6" and less is better. Keep an eye on the FVSA and try to keep it as long as possible while still getting at least .50* camber gain. You`re not going to get anywhere even close to the FVSA length of a C5 so don`t even try.
I wouldn`t say your RC experience is totally useless,just keep it in perspective. I used to run 1/10 touring myself. It was a lot of fun and it`s a great way to learn about tuning and it`s effects on how a car behaves. Just don`t expect to get quite as radical in full scale. A G body Monte front end wouldn`t help you much,they need a lot of help geometry wise and aren`t R&P friendly. I think you`re better off starting with what you have. Mark SC&C

[trackrat79]

What does FVSL realy mean. I know what the letters stand for but the measurment does not make sence to me. I lowered my upper frame pivot point measurment 1/2 inch to get my camber gain to .38 and my fvsl went form 3800 to 230.

I have two front setups at the moment. One has a static ride hite role center of -.87 and the other has a static ride hite role center of +1.13

I was wondering about the g body design because that is what nascar chassi's use as a base model for all thier front suspension. With the off parallel mounting of the lower arm to the frame. But if it would be better to stick with what I have that is closer to a corvette type than i will and it saves some work.

Thanks for your input