Opinions on Suspension Set-up

[jstricker]

I've built several different race cars for closed course road racing, open road racing, and even a few dirt track cars (modifieds). I'm going to state right up front that if the setup will work with the car I generally prefer a soft spring/stiff bar setup, but I've also seen cases where some cars simply don't like that and want a stiff spring/soft bar setup.

The Supra race cars I've assembled in the past have been Lemons cars and we've tested them out at autocrosses, mostly. We've been cutting two coils off the stock springs (whatever was on the car, I don't know how many variants in spring rates Toyota installed in the cars) and putting in some spring rubbers. This lowered the car about 1.5", give or take, and I'm guesstimating increased the spring rate about 40 pounds. We've been running the stock sway bars due to budget constraints in the Lemons series.

The handling has been "OK". The cars have a lot of push in them, you really have to get agressive to get much in the way of oversteer out of them. This isn't surprising since it's basically a stock suspension setup and most OEM's set their cars up with a lot of understeer. Lowering and stiffening the springs helps with the body roll, but not really enough. We routinely lift the inside rear tire in hard corners.

What I'd like opinions on is what the Supra chassis seems to like from people that have set their cars up for racing. Is it one of these that really likes a stiff spring soft bar setup? If so, I'd leave the stock bars on (maybe put a bigger rear bar on) and get stiffer lowering springs. If it will work with the soft spring/stiff bar setup, then I'd leave the springs the way we've been doing it (slightly stiffer and lowered) and get more aggressive on the bars.

Either way I know it's going to take some tweaking but from those of you that use the car on the track and/or autocross course, how are your cars setup?

John Stricker
Russell, KS
DOGMA Racing

 

[supraguru05]

Right now I am running 800 # front springs with the ST sway bars and still have way to much body roll on the front end. I am finishing up a calc sheet to see if I need more bar or 1000# springs. I am going to base that off of the wheel rate. I can tell you that you definitely do not want the stock bars especially on any kind of true racing tire. In order to prevent the body roll with that soft of a roll bar your spring rates will have to be to high resulting in a high wheel frequency.

 

[jstricker]

Right now I am running 800 # front springs with the ST sway bars and still have way to much body roll on the front end. I am finishing up a calc sheet to see if I need more bar or 1000# springs. I am going to base that off of the wheel rate. I can tell you that you definitely do not want the stock bars especially on any kind of true racing tire. In order to prevent the body roll with that soft of a roll bar your spring rates will have to be to high resulting in a high wheel frequency.

Thanks for the input. Your comment about wheel frequency was exactly my feeling as well given what the car is doing.

Up until now I've driven and prepped/crew chiefed the cars. With the multiple cars I've been dealing with I've crawled out f the race seat and put on my crew chief hat full time. This isn't a bad thing, I'm an old guy with 8 fused vertebrae and one eye (although I'm much more sneaky than the youngsters......) but I'm having to learn how to process the information coming back from MULTIPLE drivers on what the car is doing. That and video of the car on the track is what I have to go by.

That's not a typo, you're running 800# springs on the front? What is stock spring rate? That seems like it's almost NASCAR setup when it's being just run down on the bumpstops full time.

We can't run race tires in the Lemons series. We're limited to NORMAL street tires with a tread wear rating of 220 or higher. So far the tires that have worked the best and lasted the longest have been the Toyo Proxis 4 so we always go with one set of them mounted up and then we usually mount up another set of something else to see how it compares. Last time it was BFG T/A's that were 255 or 265 as opposed to the Toyo 245's. That didn't work. The BFG's started self destructing on the outside tread blocks about 5 hours in and after the first day were unusuable.

Have you ever weighed/cross weighed the car?

Lots to think about and any other comments are appreciated. Not suspension related, but since you're sponsor is Amsoil are you running their 0W-30 synthetic? That's what I plan to run in the turbo motor.

John Stricker
Russell, KS
DOGMA Racing

 

[rtrdpenguin]

I'm no suspension expert, but my stock springs as well as aftermarket lowering springs had massive understeer with stock sway bars due simply to the front/rear spring rate ratio being so understeer-biased. There was also a ton of body roll, as you can see from my signature picture haha. I now have some 12 kg/mm springs in the front and 10 kg/mm in the rear and handling is very neutral. There is still some body roll but with a car this heavy super stiff rates are necessary, especially in the front. My next modification will probably be a stiffer rear sway bar (and proper non-plastic stock endlinks) and stiffer front springs. I drift my car on high performance street tires so my main concern is predictability and stability, not so much outright grip on corners. So far the soft sway/hard spring combo is doing very well for my needs, and the couple other MKIII drift car owner's I've talked to all run soft sway/hard spring setups also.

 

[supraguru05]

I run castrol Ow-30 in my race car. as far as a street tire setup the springs definitly need to be a lower rate than what I mentioned. There are still some good street tires that are 220 or higher. I would still recommend the ST sway bars or better yet the whitelines if you can get ahold of them cheap. If you wanted to save some money on the cost requirements for the lemons seris you can run the eibach springs. I raced on Khumho MXs and eibach springs with st sways for a full season on road courses. The progressive springs kinda hurt the front end but the low initial rate helped the rear over the hills at mid o.