We lowered the spring collar to remove the original KW spring.
Next, we removed the OEM top hat.
We chose a 110n/mm front spring (571lbs/in) up from the standard KW Clubsport 80n/mm spring rate (457lb/in). The rear spring rate we left alone at 80n/mm but replaced the springs with 80n/mm Swift Springs. This new spring rate is virtually identical to the 2002+ NSX Type-R suspension.
NSX Spring Rate Tech:
The trend for track NSX spring rates is to have stiffer front spring rates than rear. This is due in part because the front motion ratio of the NSX is lower than the rear, meaning the front wheel rates are softer than the rear even though the nominal spring rates are the same. In addition to this, the NSX’s roll center migration drops significantly as the car is lowered. The lower you go, the stiffer the front swaybar and spring rates need to be to compensate for the loss of geometric roll resistance.
In short, the lower you make the NSX, the more oversteer you’ll get; and this is what we are trying to improve based off how our car handled in the last track test.
I’ve never quite understood Japanese NSX “tuners” and tuning shops that run stiffer rear spring rates (and thus, significantly stiffer rear wheel rates). The front to rear roll couples would be terribly different and un-coupled. But maybe it’s also to band-aid and reduce the rear camber-gain which also greatly worsens as you lower the NSX. This can (and should) be offset by running less static rear camber, which most NSX owners and shops don’t really do in the US or Japan; other than the handful who go to an extreme to reduce camber just to improve tire wear.
We replaced the worn-out rubber OEM top hat bushings with urethane ones from iLift Systems. This will greatly improve our damper’s control over the car without filtering it through a soft, worn-out bushing.
With the new bushings and Swift Springs installed, we were ready to go.
18 comments
That NSX looks fantastic. Why did you go back to the restrictive stock intake manifold and muffler?
A052’s will be my top choice for when go for new tires for my track NC, thanks to your review.
The car looks so right with 17s and 18s vs the larger wheel set. You mention the roll center debacle, but I can’t imagine there’s not correction kits made for the NSX. Have you looked into them?
Like James asked above, why go back to stock exhaust setup? Was the previous setup just too loud?
I’ll be track testing 17/18 vs 18/19 soon.
There are not any roll center correction options out there. Which is why I’ll be developing a billet upright to fix this in addition to the dry sump I designed that retains air conditioning.
The stock muffler was to make the car tolerable until the turbo goes on since the previous exhaust was pretty much straight-piped. The stock manifold was due to the gutted and ported one being modified for a drive by wire throttle which will go on soon.
How disruptive to the drivability of the car would it be to simply make both the front and rear rims sizes 18″? I know the NSX has always been designed with staggered sizes and widths of tires. Would it even be possible to standardize them?
As long as the outer diameters are within the tolerance of the ABS, 18/18 is fine and has been done a lot.
is the vid on page 6 working for everyone else? I get an error (Playback ID: zVTOmS3S9fZHDntm) when I click on it…
Is it working now?
yes, thanks!
Can you explain/educate on your driving style a little please? Going into turn 1 you say “a little bit of entry neutrality” and from what I can observe you did that by turning in sharply and then quickly reducing steering angle. Is to counter the understeer you would have gotten if you turned in more smoothly? And what were you doing with you feet when you did the sharp turn in?
Thanks
started watching your Senna vid, you said the same thing about entry neutrality for turn 1 but didn’t do the sharp turn in then dial back. Can you explain what you mean by “entry neutrality” too? I mean the words are kinda self explanatory, but I’m hoping I can learn something I didn’t think of…
Hi Bob. “neutrality” is when there is little to no steering input as the car is cornering, before the point where the car oversteers and requires counter-steer (steering in the opposite direction of the turn).
To answer your question about what I’m doing with my feet: Half of steering a car through a corner is done with the steering wheel. The other half of steering a car is with your feet – weight transfer from the application of throttle and brake. The NSX has a slower steering rack and the suspension geometry causes the car to turn more as the car is trail-braking. This causes excess rotation, which is why the car rotates and requires less steering after turn-in (“neutrality”). The Senna on the other hand, uses electronics to apply more braking force to the inside rear tire to help turn the car. This sophisticated system, combined with a quicker steering ratio, does not need as an aggressive steering input for turn-in. But as the system works, the car rotates more than the steering input and also gets ‘neutral’, requiring very little steering INTO the corner. However on exit, when the car understeers, you’ll see more steering input.
thanks for going into detail!
love the explanation
Why not get longer springs and ditch the tender springs while you were replacing them?
Longer springs will lower the spring perch height and will interfere with clearance to the tire.
The rear corner weights of the car are ~900lbs. A ~450lb spring will compress 2″ at ride height. Since there is more than 2″ of droop travel in these dampers, longer springs will still become loose and flop around at full droop travel, which is what helper springs prevent by keeping load on the springs at all times. In short, longer springs won’t solve anything and will cause more problems.
Not sure why it’s so hard to weigh stuff before you change it. When you spend money on a part, it’s kinda nice to know that you are getting some kind of improvement.
Call me an engineer, but I always weigh components, and usually break out the calipers to get specs. It’s actually really fun to geek out on this stuff.
Having said that, I really appreciate the write up.
If you read Part 4 where we cover the CE28’s, they are 17×8” +38 front and 18×9.5” +40 rear CE28s to weigh in at 15lbs and 17lbs respectively.
A052 tires in 215/40-17 front and 265/35-18 rear come in at 19 & 24lbs respectively.
Hey Billy, thanks for this! Question. How much front camber were you running