How to set-up NSX suspension for the track??

[E36S50]

Hello fellow track junkies. I have an NSX that doesn't handle very well and I am looking for advice from other knowledgeable suspension tuners. Here are some facts and details. 1991 NSX w/CT SC++(~425hp), 17/18" wheels, 215/40 & 275/35 S03's, GC coil-overs (400#F/500#R I think), Koni shocks, old (1998?) RM sway bars.
The car has way too much corner entry and exit oversteer. Forget about trail braking at anything over 50mph, otherwise you'll be in the weeds. A little background...I am a fairly experienced driver/instructor, have owned and driven many 500+hp cars, know and understand basic suspension tuning, etc. I have trid all kinds of tire pressure setting, alignment specs, shock settings, etc and the car never feels good i.e secure and controlable. I don't expect it to be as forgiving as a stock NSX but this thing is diabolical...crazy power on, opposite lock slides everywhere, and I want to tame the back end. Any suggestions?

TIA

[This message has been edited by E36S50 (edited 17 April 2002).]

 

[Andrie Hartanto]

Too much exit oversteer?! Must be the SC

Try to get a thicker sway bars up front and take the rear bars out. See if that does any good for you.

Where are you located? I'm interested to see the car and maybe get a ride for 2 or 3 laps.

 

[E36S50]

Ha, ha, yes I am sure it wouldn't oversteer as much if it weren't for all the motor goodies. I had considered removing the rear sway bar, or at least going back to the stock one. My concern was that if I got too much rear roll the tire contact patch wouldn't be ideal and the car would be worse. Are NSX's with ~500# rear springs okay without rear bars?
I am probably a loooong way from you, but the car will be running in the OTC next year so I'll take you for some laps then.

BTW, does anyone know what spring rates were in the Type S and other factory models? What about in TEIN and other CO kits?

Regards,

 

[Andrie Hartanto]

Tein uses 560 front and 670 rear.
Others can be found here http://www.nsxprime.com/FAQ/Performance/suspension.htm

I run Koni SA and H&R springs with Dali race bars setup one hole from the stiff in the front and 3 holes from the stiff in the rear. I also run -2.5 camber in the front and -3 degree camber in the rear. Toe setting of 3mm toe out up front and 1mm toe-in for the rear. With this setup, the car understeer a bit, but I can turn in consistently fast lap time than let's say if I stiffen the rear bar, and when the tire start to go away after few laps I get a car that excessively oversteer.

I would suspect the 500# spring rate is not enough, but it is worth the try. or maybe just put the stock rear bar back.

Some people that uses Tein suspension are experiencing oversteer as well in combination with dali bars. What they did then replace the rear bars with Zanardi bar.

As far as OTC, I was planning to join the fun this year. But due to personal reasons, I couldn't make it.

Your screen name imply you have a 95 M3 as well. Do you instruct with the BMW club there?

 

[ilya]

Excuse me if this is an ignorant comment as I don't know too much about suspension tuning, but should the difference between the front and rear tire sizes be so large?
215 front, 275 rear. Could that be part of the problem... maybe upgrade to some larger tires up front.

 

[Andrie Hartanto]

Ilya, the problem he is having is oversteer, not understeer. Thus going with bigger tires in the front will do much worse to his problem.

 

[Andrie Hartanto]

E36S50,

One other thing you might want to do is to go with a very beefy front sway bars. Since your problem is corner exit oversteer, this will help to get the rear wheel transfer the power to the ground better.

 

[Larry Bastanza]

Guys,

One question I have is does the car have the non-compliance bushings and toe-links? Could it be that the car is just "checking-up" as a result of toe change in the rear with the stock rubber bushings.

I am sensing you do have the car at the limit, where the rear can get loose with some unpredictable toe change.

My $02,
LarryB

 

[Edo]

Try changing that rear sway bars setting, and dialing in as much Negative Camber in the Rear as possible.
Andrie has 1mm toe in in the rear but for a car pushing that much power I'd suggest dialing in at least 2-3mm of Toe in for the rear.

The rest is a matter of balancing the car right. I suspect lowering the rear of the car just a shade might net you some extra weight over the rear and help keep it stabilized.

 

[grippgoat]

I'm with Edo. I'd highly recommend you try lowering your back end 2-3 turns on the ground controls. Maybe even more, depending on how the height is set now. The factory service manual lists ride height at the suspension mount points. You want to maintain the stock difference front to back, or less, I am guessing (hard to say for sure without knowing where the difference is right now).

This will not only give you lower CG for potentially more back-end grip, but it will also cause you to pick up a little more static toe-in. Plus, it's quick and easy to try. Shouldn't take more than about 20 minutes to do it. Just lift up that corner of the car, and have someone step on the wheel to get the tension off the spring (if needed) so you can turn the collar easily. Also, since you'll be lowering each side the same amount, it won't affect corner balance.

There's probably also some merit in the toe link suggestion, although I don't have first-hand experience with that.

Another theory is that your back end might be too low, so that it has lots of grip and you have some understeer, but that once you put the power on it snaps very suddenly. I've felt similar behavior to that when my back end was too low. However, since you said that trail braking is also dangerous, I'm guessing you're not too low.

-Mike


[This message has been edited by grippgoat (edited 17 April 2002).]

 

[Andrie Hartanto]

Forgot to say, I also have the toe-link in my car. Larry brought up a good point. I was just assuming all the suspension part is in good condition. Check the bushings first.

Lowering the rear a couple notch mostly won't improve anything especially at corner exit. It will mostly noticable at long sweeper, other than corner exit. And 1/4" is barely enough to make anything noticeable.

Putting more negative camber in the rear will also hurt your corner exit acceleration rather than helping.

I think Larry hit it on the nail on the possibility of toe change.

 

[maomaonsx]

This is the harder way to solve your problem should you run out of solutions. Try increasing the initial torque of the LSD so your car would be less sloppy coming out of the corner.

------------------
G Dummy~

Faster than stock.


Sign up for the Northwest NSXCA Track Event at Thunderhill:
http://sacramento.nsxca.org/Events/thunderhill_driving_school_4-02.htm

 

[docjohn]

I'm with larry and andre on this one,toe links and hard bush kit.Plus basic alignment/corner balance.get that all right then play with sway bars and tire pressures.also think about stiffer front springs.

 

[E36S50]

Okay guys, from my original post I'll go back to the basics. I checked my files and the springs are 500#F & 550#R. One would hope that with this little rear bias it should push, but it doesn't! It currently has approx -1.5deg on the front and -2deg on the rear with approx 6mm of total toe in. Do this sound good? I do not care about inner tire wear, I want it to stick! All the bushings appear to be in good shape but they are original 11 y/o with 50k miles. Maybe the old bushings are letting the rear suspension toe out on corner entry? Does anyone but CT make rear parts and bushings for these cars?

If all else fails I am going to disconnect the rear sway bar and give it a try.

Thanks again

 

[Quest]

I'm not much of a track freak, but I know a couple guys who do track their NSX's quite a bit and they have mentioned that the Comptech non-compliance (aluminum?) bushings made a noticable difference, because of the supposedly weak rear bushings. I don't know if this would help your problem or not since I'm not an expert, but it sounds like you have something that's flexing/deforming that's not allowing you to keep that nice toe in under heavy load. Just my $.02 I probably just proved my lack of understanding of the whole situation.

Oops just read the other responses, already suggested

[This message has been edited by Quest (edited 18 April 2002).]

[This message has been edited by Quest (edited 18 April 2002).]

 

[Larry Bastanza]

Guys,

I have to say, I am not really sure that "age" is the issue. It's rubber vs. delron, or whatever Comptech uses. The bottom line is you WILL get toe change with the OEM rubber bushing and toe links. Remember you MUST do both the toe links and the bushing on the rear beam, or you will just move the problem.

One other thing I remembered from past racing experience is a concept called "Spring Bind". If you have the car really low, or sprung too soft, or the spring is too short, you could be compressing the spring enough to actually get the coils to meet. This is why it is better to lower the spring perch rather then shortening the springs to lower the car. This is like bottoming out the shock, which will make the car "diabolical" as pointed out.

If you want to experiment, raise the ride height and see if the thing gets more controllable. If so, you can figure out how to solve it, once you understand what is going on.

Another $02;-).

LarryB



[This message has been edited by Larry Bastanza (edited 18 April 2002).]