suspension setup, tire choice. Need help

[nsxed634]

I have a Porsche, S2000, and various old MG's, TC and B. I use the S2000 for autocross - beautifully predictable and handles so well. Then I recently got a 93 NSX with Brembos and coil-overs, 16" Momo's front and 17" rear. Toyo T1-R tires on front - T1-S on rear. Car felt "sensitive" but ok. Replaced worn out rears with T1-R (same as fronts). Car is now very unpredictable, steering feels very non-linear, car actually torque steers on and off power. Difficult to drive particularly on country roads. Actually seems "disconnected" when accelerating through 80 + mph - scary when passing slower cars.

Where to start with understanding all this? Any other owner noticed a similar concern? I can't imagine new rears making this magnitude of difference, but when I threw on a pair of BFG 18's from my other car it seemed to help.

Sidewall stiffness perhaps? I really don't know. Where would be a good place to start with supension set up, toe, camber, caster etc., wheel size, tire size etc.. I really want to go through the process of fully understanding what's happening here. Can anyone help?

Ed

 

[docjohn]

Please start us off with more info.What coilovers,and how old are they? Springrates? Are your sway bars stock? what are your tire sizes and what pressure are you running them?

 

[syam]

also knowing how much the car is lowered, as well as the alignment settings will be helpful too. is there any indication that the car could have possibly been in a previous accident with frame damage and was not repaired correctly?

 

[nsxed634]

I will have to put the car back on the lift to check part numbers etc, but I believe it has Ground Control Eibach's with Koni Yellows set to approximately a mid point setting. The tires are 215-40-16 front and 265-40-17 rear, Proxes T1-R all around.

The fronts intuitively seem rather narrow, stretched over the rims which I assume makes the sidewalls pretty stiff compared to the rears. Is this significant?

Turn in is kinda stodgy with high steering effort, not light, edgy and precise like the S2000. It exhibits initial understeer on corner entry which becomes neutral as power is applied through the apex. Not a precise and easy rotation that I would expect from a mid engine car.

And the heavy at low speed (expected) becomes ultra-light at say 80 or so, almost feels like aero lift - yeah it's that light at speed. Scary actually.

How much of this is typical with manual steering rack? Contemporary reports from the early 90's seem to like the response and feedback of the manual rack.

Again, thanks for the input. I'm sure this is all simple stuff but I am right down at the bottom of the learning curve on the NSX. I appreciate all the help I can get.

Ed

 

[nsxed634]

Sorry, the tire pressures were set at 42 front, 40 rear. There is no serious accident damage apparent, in fact it is so clean and pristine and unmolested underneath that you would swear it's a new car All the paint spotting is correct etc. When I put some 18's on the rear to try to define at least some data points it seemed to improve matters. Torque steer was significantly reduced. These were BFGoodrich 265-35-18's with 33 psi in them for no other reason than I had them available.

 

[mickeylex]

Sorry, the tire pressures were set at 42 front, 40 rear.

Set the front pressure at 33psi cold and the rear pressure at 40 psi cold and see if that improves the handling. It should. 42 is far too high in the front.

 

[Scin]

The NSX will never have that darty turn in, go kart like feel that the S2000 has. That having been said, your aftermarket suspension might not be setup correctly.

My NSX with 255/35/18 rear and 215/40/17 front Eagle F1's, with Bilstein shocks and Tein S-tech springs (1" lower, 20% stiffer linear spring) understeers at low speeds. This is much less apparent at high speeds. The steering rack on the NSX is really slow for a sports car. It also takes a little getting used to not having any power steering, especially when you are going slow. Once you get used to this, it's actually quite pleasent and provides good feedback.

If you want better turn in and your Konis are adjustable, try to soften up the front some more. You can also see what sort of anti-sway bars you have and either soften up the front, or stiffen the rear (I will be buying some adjustable sways soon). The previous owner may have a funky setup on the car, he may have actually tuned the understeer out of the car by putting a stickier tire up front. This may explain some of your problems.

What I have found is that the NSX is just not a good autocross car. I'm pretty sure I can beat my NSX in my Miata (with the same tires) on just about any AutoX track, especially the tighter ones.

I would suggest taking your NSX to a road course, this is where it will truly shine and should be competitive with just about any modern sports car. If you car is not completely funky (check alignment), it should really feel great and be very fast.

You should also get your car aligned at a reputable Acura dealer or performance/race alignment shop ASAP. If you don't know where to start, do a stock 91 alignment... this will give you a pretty aggressive alignment that handles well (it will also wear your tires out more quickly then some people like, hence the reason the alignment specs were changed later... lots of owners bitching about tire wear).

 

[stuntman]

For the Koni Yellows remember:

Counter Clockwise = Stiffer / more rebound damping

Clockwise = Softer / less rebound damping


Stiffen (CCW) your front dampers for more responsive turn-in.

Try 33-35psi all around (or 33f 35r) if you like the higher rear split (which I wouldn't reccomend for track use).


What are your spring rates?

 

[nsxed634]

700 # front. 800 # rear springs. By the way, I set the Konis to full soft which seemed to improve overall feel.

I am considering TIRE/WHEEL change, perhaps 17-8 FRONT / 18-9.5 REAR. Any thoughts?