Dialing out Understeer

[Stew]

Ever since I bought my Zanardi edition, I've really liked the car but there are a couple of things that bug me about it.

1) Understeer - this car just understeers WAY too much. What would be the best way to cure this problem without changing the entire suspension? Smaller front sway bar? Larger rear bar? Less firm front springs? How about shocks? I like the ride (firm but not punishing) so don't want to affect that too much. Playing with tire pressures helped a little but not nearly enough. Any advice would be greatly appreciated.

2) Manual steering - it just seems to make the car feel heavier than it is. It is also hard to make quick transitions in the wheel. How good is the electric power steering? Is there enough road feel? Does anyone know if it can be retrofitted to a manual steering car?

 

[ChopsJazz]

Stew, most track cars dial out understeer by softening the front sways and stiffening the rear. I haven't personally done this with my car, but that seems to be the answer.
As far as the steering is concerned, I love the steering on my '91 (manual) and wouldn't trade it for the world. I don't feel at all that it makes the car feel heavy. But instead I feel a lot more connected than the newer models with the electric rack. I suppose it does make parallel parking a little tough, but that's a pretty small price to pay for the sensitivity and direct input that it imparts IMO.

 

[ScienceofSpeed]

Hi Stew --

I'd recommend getting a set of Dali (www.DaliRacing.com) Race Sways to be able to dial out understeer. There are other ways including shock/spring suspension modifications, tire pressures, however, I've had most luck with the race sways.

The liveability of the manual steering rack can be improved my neautralizing the toe in thr front of the car. This will allow better low-speed driveability.

The power steering rack can not be easily or cost-effectively retrofitted to the non-PS cars.

Cheers,
-- Chris

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[nsx1164]

Originally posted by ChopsJazz:
Stew, most track cars dial out understeer by softening the front sways and stiffening the rear.

I thought it was the other way around with NSXs. I thought most NSX shoes were going more towards a stiff front/less stiff rear setup (based on suggestions from PD Cunningham awhile back), presumably to reduce understeer (or increase oversteer) and allow them to more easily rotate the car with the loud pedal.

Settings done for both swaybars and shocks (for those with Koni or other stiffness adjustable units)


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Manuel C
93 NSX S/B #394
93 300CE
93 NH750

 

[ScienceofSpeed]

The basic concepts of suspension setup is the same in every four wheeled car. A stiffer rear sway will increase roll resistance, decreasing understeer.

Read this: http://www.nsxprime.com/FAQ/Performance/swaystrutbars.htm

Brian St. Denis has some good points: "The stiffer rear sway bar would resist body roll and apply more force to the outside rear tire instead of applying so much to the outside front tire"

-- Chris

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[Stew]

Thanks for the info. Do I assume correctly that a stock Zanardi version has non-adjustable sway bars? Also, Chris, why do you suggest Dali's racing sways as opposed to their street sways? I do not want to affect ride quality much. I also find it strange that according to Acura's literature, the rear bar is stiffer than stock (they don't say by how much) but the front bar was left unchanged. If everything else was left the same, this would decrease understeer as compared to stock, not increase it. But I believe due to the increased front spring rates over stock, this is what caused the increase in understeer.

 

[maomaonsx]

Understeer - this car just understeers WAY too much. What would be the best way to cure this problem without changing the entire suspension?

Drive faster. At higher speeds, the NSX should be very neutruel.

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For some, it's a compensation.

 

[nsxtasy]

Drive faster. At higher speeds, the NSX should be very neutruel

...and (above 35 mph) there is no power assist from cars equipped with power steering anyway.

 

[ak]

The other day, I was pushing my car on a 270 degree onramp and the rear seem to slip out a little while doing about 70 in 2nd gear. My car is stock 94. It was very easy to correct it with throttle...how amazing. Maybe I'm too used to FWD but NSX seems to be very neutral to me.

 

[ScienceofSpeed]

I recommend the race sways (which are the middle range stiffness he offers) as I believe they offer the maximum range of adjustability. Let Mark know I sent you

Cheers,
-- Chris

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[sjs]

As stated accurately above, stiffer rear bar yields less understeer. Assuming your rear bar is not adjustable, I would check the rates of the bars supplied by Dali and others, then select one which is adjustable over a range from equal to or below the one you have now to significantly stiffer. I would not mess with the front bar if you are pleased with the way the front end works over bumps and around corners (not counting the “push” of understeer).

The prior remark about driving faster is more important than it might have sounded. There is often a tradeoff necessary between balanced handling at low speeds and high speeds. Adjusting roll stiffness to give a “tossable” feel at low speeds can result in an edgy rear prone to oversteer at high speeds.

 

[Number9]

Keep in mind that the Zanardi has different springs, shocks, and sway bars than a regular coupe or T so it's not directly comparable to any other NSX model.

It does understeer, but I don't find it as objectionable as you (Stew) do. The main problem is that the stock NSX-Z car doesn't have enough power/torque to be able to use throttle-on oversteer to bring the rear out whenever you want it to. If you leave the suspension alone and get a turbo or SC, you'll find you can bring the rear around with judicious throttle application which you can't really do with the stock NSX-Z setup, except in the higher rev range. Strong stock engines have 200-205 peak torque at the rear wheels. With the SC you'll have that much at all times over 2.5K RPM and you can step the rear out at will. With a turbo, you'll have to be careful not to swap ends!

As for the the heavy steering, I agree. I had a 95 NSX-T with PS and really liked the steering. In contrast, the NSX-Z steering is very heavy even though the steering ratio is NOT that quick, so it's a chore in courses with repeated tight turns. So get used to the workout or get a different car for that type of driving.

Finally, as for the suspension I find it closer to punishing than firm. The Ts are overly soft, but the stock non-Zanardi coupes seem to have it about right for street use. YMMV.

--twc

 

[nsxtasy]

As for the the heavy steering, I agree. I had a 95 NSX-T with PS and really liked the steering. In contrast, the NSX-Z steering is very heavy even though the steering ratio is NOT that quick, so it's a chore in courses with repeated tight turns.

My understanding is that the power steering does not provide any assist above 35 mph. And on all the courses I know, even the tightest turns are at least that speed. So there shouldn't be any difference on the track between the Zanardi and the non-Zanardi.

 

[Number9]

We've got some switchbacks and hairpins in the Santa Cruz mountains that you can't take in an NSX at 35 and the PS helped quite a bit on those. A quicker steering ratio and PS would have helped even more...

--twc

 

[Stew]

Thanks for the responses. A little more info about the understeer problem: most of the roads in my area are relatively slow speed; very windy and hilly... so I would like the car to behave a little more neutrally at those speeds (usually < 60 mph). The understeer is especially noticable in trail-braking situations: coming down a straight into a turn with some braking the car just doesn't want to take a set and turn in too eagarly. There is always that moment of hesitation and slide before the car wants to turn. It's darn scary sometimes... I expect the car to turn in and it just doesn't want to. I'd rather have the car balanced slightly toward oversteer so that it will rotate easier to get around these tight, relatively slow turns. The steering is the same situation. It's sometimes a real workout to go from one curve to the next on these roads. I also believe (like twc) that the steering ratio could be a little quicker.

 

[sjs]

It doesn’t sound like NSX handling, except to the degree that any mid or rear engine car feels a bit light in the front. What tires are you running and have you had the alignment checked lately?

You say you've played with tire pressures front/rear, but you might look at higher overall pressures when playing hard if you are running near "spec" now. Aggressive cornering in tight turns (such as an autocross) can be particularly tough on sidewalls, slip-angle etc. Your symptoms sound a little like that. Of course, you always want to change things gradually and get the feel of it before pressing your luck.




[This message has been edited by sjs (edited 05 June 2001).]

 

[Stew]

I have another mid-engine car that does not exhibit this type of behavior; the car is a 1971 Porsche 914 which was converted to a 6 cylinder, 911 brakes and suspension, etc. Anyhow the steering and turn-in are MUCH more eager than in the NSX. It's also easier for me to slide and balance it at the limit. Of course it also weighs about 700 pounds less than the NSX. I still think that there should be a way for the NSX to approach this type of behavior with the proper setup.

I'm running Michelin Pilot Sport tires and currently running at near stock recommended tire pressures. I like these tires more than the OEM Yokos and hope to get more mileage out of them. The alignment was checked recently and is at or near spec.

 

[nsxtasy]

This handling is definitely NOT typical of an NSX.

I think your tires might be causing the problem. The OEM Yokohama A022H tires are unsurpassed at having a precise turn-in. You're sacrificing this by using the Pilot Sports.

It's also possibly the alignment, as mentioned by others.

Are you coming to the River Run event on Saturday? (Details at http://www.nsxprime.com/ubb/Forum2/HTML/000005.html) You might consider doing this, and letting someone else drive your car to see what they think of its handling. Dave Davis will be there, and he's probably as qualified as anyone to check it out. (He's a very experienced racer, as well as owner of Davis Acura, the dealer with the biggest NSX specialist service department on the East Coast.)

Incidentally, regarding the 35 mph thing, I assumed the word "course" was referring to race tracks. Obviously there are mountain roads which demand slower speeds.

[This message has been edited by nsxtasy (edited 05 June 2001).]

 

[Number9]

I'd have to concur with nsxtasy on this one - I've got the same car with the stock Yoko rubber and the turn-in is crisp and immediate. Did your car behave this way before you switched to Pilots? I've got Pilots on my other car and they do feel a bit softer, maybe less stiff sidewalls...

--twc

[This message has been edited by Number9 (edited 05 June 2001).]

 

[Stew]

I don't think the tires are the problem. In fact the Pilot's seem to react a little better than the Yokos in my opinion. The alignment could be a little off, but I believe that this is just the way the car is supposed to behave with the suspension settings given to it. Remember again that the car is the Zanardi version which has substantially increased front spring rates vs. the rear as compared to the non-Zanardi versions, which would exascerbate the problem (more understeer). I also believe that no amount of tweaking will give the same feel as my older Porsche. This is the one area that that car excels: steering and road feel. The car feels very light on it's toes and turns and rotates very easily. Remember that I'm talking slower speeds: this tendency at slower road speeds starts feeling twitchy at higher speeds. At higher speeds, the NSX definitely feels more stable. I would still sacrifice some of that higher speed stability for lower speed rotation.

I was planning on going to the River Run event, but I noticed the event too late and according to the NSXCA web site, they wanted registration by May 29th which I would have missed.

[This message has been edited by Stew (edited 05 June 2001).]

 

[ScienceofSpeed]

NSXSTCY sez:
//My understanding is that the power steering does not provide any assist above 35 mph. And on all the courses I know, even the tightest turns are at least that speed. So there shouldn't be any difference on the track between the Zanardi and the non-Zanardi.//

It is true that the power assist steering system in the NSX cuts boost at 35+ mph. However, there is additional componentry (gears, rods, etc) that is on the column on the PS cars. The 'feel' is different, even above 35 mph. On a full-track car, I prefer the non-PS cars. On a track/weekend/freeway car, I actually prefer the PS cars.

-- Chris
(have owned both PS x1 and non-PS cars x3)



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