Need some advice lads.
For the street I have changed to Enkei forged 19" split spoke wheels, to fit over the StopTech 14.1" big brake kit. Michelin Pilot sport 245/35 F and 275/35 R. Everything ok there.

For the track I cannot use the stock Infiniti wheels, because even though they are 18", they do not fit over the Stop Techs. And they weigh too much anyway, at 24.5 pounds. So probably going to the approximately 18 pound Nismo wheels at 18", as they do fit over the Stop Techs and are pretty good value.

But the tires are a conundrum.

Stock tires are 225/45 and 245/45 respectively. That makes for a 25.8 inch front diameter and 26.8 inch rear diameter.

Track tires have very few size selection choices that will fit, and these seem to be the best alternatives: (Michelin Pilot Sport Cup) are 225/40/YR18 front and 265/35/YR18, and thus have diameter of 25.1 inch front and 25.2 inch rear. Pirelli P Zero Corsa are about the same at 25 front and 25.1 rear diameters for the same size tire. Hoosier R3S03 are sized a little differently, with a diameter of 25.3 inches front and rear, sizes being 245/40/ZR18 front and 275/35/ZR18 rear.

The obvious concerns are:
1) the stock set up is an inch taller in the rear than it is in the front, while the track set ups are all essentially the same height front and rear. What problem if any will that cause, especially with VDC.
2)the stock set up is about .7" taller in front, and 1.6" taller in the rear, than the track set up.

Variance to true readings on the speedometer are not important at all. But having VDC engage just as a result of speed would be nasty, though I can turn it off. Any other issues to be concerned about? Anybody else having this much brain cramp over finding a good tire and wheel combo for the track?



Cpe 6MT/Aero/Prem/ATI/RT cats/Borla hdrs-catbcks/Nismo flywhl-cltch/TS-ECU/Tein flex EDFC/Stillen sways

 

Ed,
For the most part, you will be ok as long as you maintain the F/R diameter ratio. There's no need in preserving the OEM diameter unless speedo and odometer accuracy is of interest here and I doubt that is hardly the case.

The closer you can get to stock F/R ratio the closer VDC will react in a manner you are accustomed to. If you have a choice of going under or over slightly, I'd recommend going under. I've experimented with both and found going over packs a nasty surprise! You'd think by going over you'd have more room to 'play' before VDC stops the fun. While that is actually the case, but when VDC do decided to 'cut you off' in the middle of a drift with the appropriate counter-steer, your are greeted will a hard hook to the outside like a newbie lifting off durring a drift ... a big NO NO and sometimes very costly! Certainly, the situation grows expinentially worse the further away you deviate from the center. In my case, I was approx. I.5% over ... not horrible, but enough to annoy me. Your milages may differ!

My current track setup is 6% under the OEM size and roughly 1.0% under the F/R ratio. Because is it slightly under, VDC does kick in just a tad earlier, but if you learn to be smooth it'd hardly engages. It also has the added advantage of a slight increase in rear wheel horsepower due to a better overall gearing ratio.

I'll help you looking into a set of nice R tires.

Clint (THX723)

 

What about Toyo RA-1s?

225/40ZR18: 25.1
275/35ZR18: 25.55

 

Also a very good tire. Was not sure if the 50mm versus 40mm difference in width was material as between front and rear (I assume not). The Michelins cost more, that is for certain.

Cpe 6MT/Aero/Prem/ATI/RT cats/Borla hdrs-catbcks/Nismo flywhl-cltch/TS-ECU/Tein flex EDFC/Stillen sways

 

I'd advice against running 225/275. You will experience excessive understeer, unless you increase the front trac or reduce the rear. I'm currently running 225/245 and is already experiencing some 'push' at the edge. But it's not severe and should be addressable by a set of sway bars or perhaps change of front spring rates.

In your case, I'd stick closer to 245/275 if possible.

Chosing the right overall diameter is only 1 part of the 3 parts equation.


Ed,
What's you 'track' wheel width measurment?


Clint (THX723)<P ID="edit"><FONT class="small"><EM>Edited by THX723 on 02/16/04 02:28 PM.</EM></FONT></P>

 

Clint:
The track wheel is to be, I think at this juncture though I can change it, 8.5 inches front and 9.5 inches rear, with 225/40 front tire and 265/35 rear tire.These are the recommended wheel sizes for the tires.

Although I have done a lot of driving with the VDC off, I liked being able to take the first half of the laps at Laguna Seca with it on, then doing a few with VDC off, then putting it back on and trying to be more aggressive, and just slowly working up the scale so to speak. There was a little comfort zone to doing it that way. Once I get more skillful and learn the car better, it probably won't be necessary to be so cautious, but I would rather learn slower and not get a real brutal education quickly.

Cpe 6MT/Aero/Prem/ATI/RT cats/Borla hdrs-catbcks/Nismo flywhl-cltch/TS-ECU/Tein flex EDFC/Stillen sways