Need tire size help!! R compounds!!
 

I need some R6's for the track and am stuck. I have the sport package and a spare set of OEM 18's that currently have R6's in the size of 245 F/285 R on them. I would prefer to get my next set for the 19's because the height of the tire would be closer to stock since the profile is only about 30/35 on the 18's or 19's. Anyways the place I get them from only have 235/295/325 width in the 19's. Can I run a 295 front and 325 rear on the stock 19" rays safely or will I have problems?? I had issues with scrubbing the front tires (rears still have another day in them) due to massive understeer, so I got some swaybars on the way to help with that. Would too wide of tire make this problem worse?

I could do it safe and run 235 F/295 R but that's no fun for the fronts!! I saw a 370z with 295 front A6 yesterday at an autocross event that looked fine (and drove well) but I'm nervous about rubbing in the rear and front for that matter with such a wide tire. I suppose I could also do 295 at all corners but like the staggered set up best, and 235 seems like it would be a downgrade from my 245 F 18's now...

if you track the car, please dont stretch a tire like they do in autox.

as far as size, try to keep front and rear the same. of course you are getting understeer with 245f and 295r. mine is bad with 265/285, i will look to do 275 or 285 all around next season

So will 295 be too much up front?

If you get swaybars expect understeer to get even worse unless you also increase front camber.

I run aftermarket 18" wheels for the track, 10" front, 11" rear. Currently I have NT01's on there 275 front, 315 rear. This setup worked okay but some more front grip would be nice.

on stock rims yes, i would go with 275 or 285. remember you also have to consider your suspension and power level.

I have an idea of my ideal set up, but the issue is that I am limited to the 19's to only 235/295/325. Can I fit a 295 on the front rim?

You should be able to fit 295 on there

OP, given your case with really wanting to use your 19" wheels (for some reason), your best bet with the available 19" hoosier A & R tire sizes is to go with 295 all the way around... You should be fine with that and be able to fine tune the rest of the car from there.... Let me know if you have any more questions or need any help... (however it would be much better to use your 18" wheels you mentioned)

agree with scott, but personally i like to be safer and go slightly narrower. I don't want to stretch the fronts too too much.

Thanks to you and everybody else for the suggestions. Why is it bad to use the 19's? The reason I wanted to was because the profile is the same whether I go 18 or 19, so the tires end up being about an inch or so shorter than stock.

So anyways I ended up just replacing the two fronts on my 18's with two Hoosier R5's and am hoping that I can get everything fine tuned and worked out within the next few trackdays as far as best setup.

19's generally weigh more as a unit and definitely cost more to replace. It's already not cheap to go to the track, why make it more expensive than necessary?

18" setup will be lighter (decreased unsprung weight = better handling, improved acceleration and braking), and cheaper too.

As long as you stay close to the stock diameter, you should be okay. I once used 265/30/18 on my car, it didn't seem to do any harm. I plan to run 275/35/18 all around on my 18s. I believe stock is somewhere around 26.5" in diameter, there aren't many race tires in that range. I believe I was looking at diameter that were over 25".

I run 18s because I am on a limited budget, cant afford to buy another set of tires.

You should talk to my guy, he sells nearly full tread R6's for $90 a tire.

Glad to help..... But it's not usually the best of ideas to only replace 2 performance tires (or any R compound, especially Hoosiers). The balance will be thrown off being that the used rear tires will have many more heat cycles and will be significantly harder and less responsive, slower to heat up, etc than your new front tires will.
This decision will likely yield you a set up that is much more prone to oversteer, and the tires are likely to "come in" or get up to temperature at much different points....
Since you already decided to just get the two new (softer stickier) fronts and leave (much harder and heat cycled) used rears........ Just be aware of the effect you may get.