Looking to dial out understeer

[Nihilation]

So here's the deal, I have Bilsteins with stock springs on the lower perch setting. The wheels are Enkei RPF1's, 17x7.5(215/40) up front and 18x9.5(275/35) in the rear on RT615's. Grip is phenominal, except for slower speed tighter turns where it understeers like a mofo. Obviously I created more understeer than normal by going with this tire size combo, but that's what I want to keep. So I'm thinking of some cheap options to correct this.

I notice that I have a good gap in my front fenders where my tires aren't really flush. I think I could get away with a set of spacers up front to widen the track in turn dialing out some of the understeer. Do you track guys think this is a good route to take before spending the ~$300 on swaybars?

Maybe combine that with a Zanardi rear swaybar? I would like a little less body roll too.

 

[VBNSX]

What sways do you have?

If you have adjustables, just increase the tightness on the rear. If not, I'd suggest a bigger rear sway. I don't know if the zanardi is any bigger but the comptech sways are definitely bigger which would give you less roll and if you adjust it properly I'm sure you'd get the oversteer you want.

x

 

[GeNSX]

Sounds like sways are the easiest way to go.
Some track rats on the IS300 forums like to go with stiffer shocks/spring and leave the sway as they seem to think of it as a band-aid for the understeer.
Another option is to adjust the brake bias so that it's a bit more rear tire oriented... but that's pads / fluids and possibly messing with the master brake assist cylinder yada yada...

Good luck on your quest for the perfectly neutral car.

Max

 

[VBNSX]

Or... if you want something free... increase the rear tire pressure. It may put it out of the temp zone but it'd work..

x

 

[W]

If you're already happy with high speed cornering, learn to trail brake the slower speed corners.

 

[BioBanker]

Im running RA1s with a worse profile than what you have (Im 205/275), and I do not perceive understeer on the track at any speed.

Ive stiffened up the front with 12k spring rates vs 10k rear, put NSXR chassis bars and the front Comptech sway (I left the rear off).

Maybe your alignment?

 

[Nihilation]

Factory sways and springs, just Bilsteins. My alignment is within OE spec as far as toe and caster go, camber is at -.5 in the front, -1.3 in the rear.

I'll check my tire pressure out. Higher speed feels OK for sure, it's the slower speed tight back road stuff that kinda sucks. Portions where my BMW would whip around no problem the NSX plows.

 

[2slow2speed]

The 215/40/17 and 275/35/18 setup that you have will tend to understeer on the slower speed corners when applying throttle (that's the only time that I notice that on the NSX with a similar setup)

W mentioned trailbraking, given that you used to drive a BMW you probably already know that. If you are experiencing understeer while powering through/out of a turn then trailbraking is not applicable.

I run my NSX with alignment settings that are a lot more aggresive than yours and the car does experience throttle induced understeer when the front tires overheat at the track. A wider tire up front will probably help with that.

Maybe clarifying when your car experiences understeer will help other folks chime in with better advice.

Ken

 

[nsxtasy]

The 215/40/17 and 275/35/18 setup that you have will tend to understeer on the slower speed corners when applying throttle

You might try 265/35-18 the next time you replace the rears...

 

[FF2Skip]

Like Josh, my experience is with a tail-happy car that had more power and currently have a 215/18F/275/19R combo on the NSX. The car is equipped with JIC coilovers. Any idea how much understeer I might be able to reduce simply by corner-weighting the car? TIA... Skip

 

[Nimbus]

OE spec alignment simply doesn't cut it at the tracks. I would adjust alignment first before changing hardwares throwing more variables in your equation.

 

[mickeylex]

Here is a good guide - starting point for adjusting understeer/oversteer. Brought to you by Roger Krause Racing: http://www.rogerkraustires.com/overundr.html

Handling is adjustable in many ways and this page might help you figure out what to change.

 

[Nihilation]

Here is a good guide - starting point for adjusting understeer/oversteer. Brought to you by Roger Krause Racing: http://www.rogerkraustires.com/overundr.html

Handling is adjustable in many ways and this page might help you figure out what to change.

I don't think that site is correct when it comes to tire pressure. For example under "Understeer Corrections" it states to add more front tire pressure to reduce understeer. Brrrrt. Wrong. That would add even more understeer. Decreasing front tire pressure would reduce understeer.

 

[Hrant]

I have found this cheat sheet quite helpful:

http://www.daliracing.com/v666-5/info/camber.cfm

 

[dquarasr2]

I don't think that site is correct when it comes to tire pressure. For example under "Understeer Corrections" it states to add more front tire pressure to reduce understeer. Brrrrt. Wrong. That would add even more understeer. Decreasing front tire pressure would reduce understeer.

Of course it depends on whether the tires are near optimal pressure, and already above or below optimal. In general, though, adding pressure INCREASES grip. You lose more grip being underinflated vs. being overinflated. Adding pressure to the front should indeed reduce understeer, again, in general.

As mentioned already, check alignment. It's a relatively inexpensive way to change the handling characteristics. Maybe add a little toe out to the front.

 

[titaniumdave]

Try increasing the front camber to -1 degree, set the toe out to the minimum (.01 degree, 1 mm) and see if that helps. I like -2 degrees front, -2.6 rear camber. I find with 0.1 degrees toe -front and +rear I get very stable braking and fine tire life.

I like to do an auto cross turn for slow speed turns, go in a little hot, throttle lift just after turn in and get the rear end to start to kick out. As the car rotates, lightly come on the throttle when the car is pointed down track to get the rear end to hook up again. All this should happen well before you hit your apex and you should be under full power when you hit the apex for a fast exit speed.

 

[nsxnut]

I have found this cheat sheet quite helpful:

http://www.daliracing.com/v666-5/info/camber.cfm

Better yet...

Carol Smiths book. Engineer in Your Pocket

http://www.pegasusautoracing.com/productdetails.asp?RecId=163

Carroll Smith has now produced a handy pocket guide to field-engineering a racing car. This wire-ring-bound, laminated guide to the cause-and-effect tuning of a race car is ingeniously separated into problem/solution and cause/effect sections for quick and easy reference.

I have this book. Recently gave one to a friend as well.

Later,
Don

 

[apapada]

I don't think that site is correct when it comes to tire pressure. For example under "Understeer Corrections" it states to add more front tire pressure to reduce understeer. Brrrrt. Wrong. That would add even more understeer. Decreasing front tire pressure would reduce understeer.

No, it's the other way around. Lateral Grip increases with increased lateral stiffness of the tire. In order to get higher cornering forces and increased lateral (cornering) stiffness, you need to ADD pressure. Of course this works up to a point (45 psi for most tires). Afterwards, the tire's footprint changes.

Of course it depends on whether the tires are near optimal pressure, and already above or below optimal. In general, though, adding pressure INCREASES grip. You lose more grip being underinflated vs. being overinflated. Adding pressure to the front should indeed reduce understeer, again, in general.

Very well stated.

 

[nsxnut]

No, it's the other way around. Lateral Grip increases with increased lateral stiffness of the tire. In order to get higher cornering forces and increased lateral (cornering) stiffness, you need to ADD pressure. Of course this works up to a point (45 psi for most tires). Afterwards, the tire's footprint changes.



Very well stated.

This depends...

If the tire pressure is high enough where the contact patch is already reduced than increased pressure would yield more under steer.

45psi for hot pressures on the track is on the high side...
Correct tire pressure can make a huge difference.

Hot pressures are around 30 PSI Front and 35 rear. This depends on the tire.

My current tires Michelin Pilot Sport Cups last weekend I ran 28 front and 33 rear. These were derived with a probe type pyrometer.
It was also Hot out....

Later,
Don

 

[Hrant]

Don, did I really read that you actually used a pyrometer on the track :tongue:

 

[nsxnut]

Don, did I really read that you actually used a pyrometer on the track :tongue:

Yea probe type... I also have a real nice IR one as well..

For break rotors I use temp paint...
http://www.pegasusautoracing.com/productdetails.asp?RecId=4974

Later,
Don

 

[92 white 0650]

Re: Hey Hrant, ole buddy, ole pal........

did I really read that you actually used a pyrometer on the track

Hey Hrant, yeah, like all his cool stuff, he's got one and he said I could borrow it. So, will you check my tire temps when I come into pit lane at Sears on 7/21? I been meaning to tweak my set-up.

 

[nsxnut]

Re: Hey Hrant, ole buddy, ole pal........

Hey Hrant, yeah, like all his cool stuff, he's got one and he said I could borrow it. So, will you check my tire temps when I come into pit lane at Sears on 7/21? I been meaning to tweak my set-up.

Sure thing... I'll lend it to you...

Later,
Don

 

[Scin]

I have a 17/18 stagger with a 215 in front and 255 in the rear with bilstein shocks and tein s-tech springs. I have the same problem with understeer at the slower speeds. My problem is mostly at turn in, after turn in I can accelerate out of the corner comfortably.

Trail braking really helped me, I also do a gentle tap at some corners to load the front end up before doing the turn.

You may want to try dialing as much negative camber you can get out of the front (probably 1.5 degrees), if you aren't happy with this, stiffer springs or sways seems like the next step.

 

[2slow2speed]

I have a 17/18 stagger with a 215 in front and 255 in the rear with bilstein shocks and tein s-tech springs. I have the same problem with understeer at the slower speeds. My problem is mostly at turn in, after turn in I can accelerate out of the corner comfortably.

Trail braking really helped me, I also do a gentle tap at some corners to load the front end up before doing the turn.

You may want to try dialing as much negative camber you can get out of the front (probably 1.5 degrees), if you aren't happy with this, stiffer springs or sways seems like the next step.

In your particular case with slow corners try what Dave (titaniumdave) suggested it's one of the few ways that you can get the NSX to rotate quickly on slow speed turns, if done properly it will allow you to get on the throttle sooner It's an advanced technique but well worth learning/practicing for sections of Buttonwillow and for sections of Streets of Willow.