I originally was going to just email Lee Grimes these questions but figured there might be a few other suspension gurus who could offer some insight. My GSR road race car has the H&R Type R cup kit suspension. As I understand it, the default spring rates for this setup are 950lbs front and 800lbs rear (it is a dual spring setup). The dampers (from what I understand) are somewhat modified and revalved Bilstein units. Last year I ran the Kumho Ecsta V700 in 225/45/15. I run a huge adjustable Ground Control rear sway bar and have a KAAZ LSD.

On to the problem. The car understeers everywhere and all the time and gets progressively worse the longer I am on track. Nearly every race that I lost, I lost by a few car lengths and during the last few laps of the race. I generally turn the fastest qualifying lap and the fastest race lap in class yet often lose because the car goes away late.

I don't understand this whole JDM vs US suspension setup even after reading the threads. I am not a tuner. As a new racer what I don't understand is how much understeer is normal vs how much is related to setup. I know most people in HC run higher spring rates in the rear than in the front. Is my best bet to get some higher rate springs for the rear and try them out at an open track day? I fear that if I go too high in the rear though I would need to get the shocks revalved.

As an aside, how much slower would a 205/50/15 Toyo be than a 225/45/15 Kumho? I spent way too much money on tires last year. Though I am very competitive, if I can quit shredding my front tires I think I would like to run a cheaper option than the Hoosier or Kumho.

Thanks for any help!


[Modified by chrisb, 10:36 PM 2/9/2003]

 

this has been hashed out quite extensively. if you read all the threads on this subject a) you'll have an effin migrain from reading a computer screen for 4 days straight and b) you'll have a really good idea of which way to go to do what. look for threads from scott a.k.a. rr98itr and ignore any rebuttle you see from me, it will only get you more confused.

nate-who thinks maybe you could just follow the pack and do a simple 800fr/1100rr setup.

p.s. yes, the ra-1's will be a little slower then the kuhmo's.

 

Really? I didn't know that.

 

Yeah, I read some of the threads. Hence why I mentioned them in my post in hopes that I could get a reply that did not consist of "do a search". (This is not a barb at you in particular but it does seem to be the preferred response of the "in crowd" h-t members.) As for those threads, I think much of the time the participants spent more time belittling each other or trying to wow one another with their extraordinary expertise in said subject than actually just trying to offer helpful responses. I don't guess anyone else has the H&R coilover kit? I know Adam Curpier has it but he does not seem to have the understeer problems I do. I wish I understood why.

 

https://honda-tech.com/zerothread?id=285747

 

Chris, do you have the 22 or 25mm GC bar?
What swaybar's on the front of the car?
Is is possible to switch the springs front to rear?

 

what are you running for tire pressures? what is your alignment like? toe, camber, caster? i assume the 225's are at all four corners. what are your rear tire pressures? if your shocks are adjustable, how are they set? what is your ride height? what is your vehicle weight/weight distribution?

and the hardest one: are you over-driving the car?

even harder ones: is your rear sway bar binding? are you running out of front travel? to you have too much negative/positive rake? could there be some aero issues?

what phase/type of corner are we talking about here? are you taking the corner too deep or underdriving the corner entry and over-accelerating coming off the turn?

how new are you to racing? have you done any schools/prior racing experience? (autocross, etc.)

nate-see why "please search the archives" is an easier answer?

 

Man, I wish I knew more about this car. Stock sway bar up front. I don't know if the springs can be swapped front to back. Nick (guy who sold me the car) said that the springs are standard springs that can be purchased from GC. The GC bar is the one that they don't sell anymore because rice boys were putting them on their car and spinning at high speed. I think 25mm.

By the way RJ, that post by RR98ITR is awesome. Unfortunately, I am not a mechanical engineer. I was lost after.... "rear spring motion ratio is better than the front, a given spring rate on the rear produces a higher wheel rate than it does on the front. We can therefore continue for the purpose of discussion to refer to the NA setup as high rear bias and the JDM as high front bias." bias? motion ratio? Uhh... and that is why I snuck by with a C in physics.

 

Definitely easier. But not more useful. That is the problem with forum only sites. An articles section detailing what could contribute to an under steering car and how to investigate and remedy the situation would be great. (But that is the webmaster in me talking.) But just the questions you posted have me really thinking. Of course the answer to many of your questions is I don't know. But I am going to try to find the answers to some of the questions.

 

Motion Ratio and Wheel Rate:

http://eaglewoman.simracing.dk/cobra...otionratio.htm

 

Chris, check your email.

 

chris - have you read the "physics of racing" series? I think its linked in the FAQ.... check it out

 

Understear eats Kumhos for lunch. I used to chew through those at a high pace on my old setup. Tire wear seems to be much better for me on my 400/550 setup.

Try:

* Swap the springs front to rear
* Change out to some ERS springs
* Tighten the rear sway a bit more

Your car was running well and you were setting some fast times, if the only bad handling your car had was some corner entry understear, once you fix that Rice and I will be in trouble.

Better yet .. I think you should but some 200# springs in the rear. That will make you faaaast!

 

1. Keep the Bilsteins. Shocks are expensive and those are good ones. Don't mess with them.
2. Assuming your coilovers will work with 2.5 inch ID springs, get some 800f and 1000r eibachs from OPM. with your big assed rear sway I don't think you need more than that in the rear. Your shock valving should handle it just fine.
Otherwise as mentioned, if the lengths are OK just swap the front and rears you currently have.
3. Fine tune oversteer with the rear bar.
4. Learn how to trailbrake and apply throttle more smoothly. As someone that was very close behind you a few times last year I can say you need to work on these things. That'll help your front tires out ALOT.

and...

5. I was faster on used 205 Toyos this weekend than I was on slightly used (still showing holograms) 225 Hoosiers. Same conditions, same track, same driver, same car. Now I KNOW that Kumhos and Hoosiers are 1 to 2 laps per lap faster than those slow-assed Toyos, so it must've been my busted *** driving. So you probably want to go ahead and ignore what I've said here (and phatty, and Alex, and metalworker...) and take Nate's (and others) advice. Kumhos are definately faster .

 

I have to say taht rr98itr is one smart cookie.

I get more and more confused, and when i finally think i have a grasp on any bit of suspention and driving, i read one of his posts and feel as if i know nothing.

Great thread,
That guy is a walking,talking textbook!

 

Hey Chris-

Autozone is having a clearance on APC coilovers this week

 

Some things to try:

1. Pull the shocks off the car and see if you can switch the springs front to back. If you can, do it. That way you wont need the shocks revalved.
2. You can try toeing out the rear a bit.
3. Replace the rear trailing arm bushings with something that is not the stock rubber piece if you have not done so already.
4. If the shocks are adjustable, turn the rears all the way up.
5. Trick the car into rotating by slightly overinflating the rear tires.