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.

Used race tires, R-compound tires, slicks, etc are more often NOT worth the headache. There are too many variables to be concerned about....
Like:
A) Are you getting a matching set off of the same car, used in the same session?
B) How many heat cycles are on them? The more they are heated up and cooled down the harder they get.... Also remember some tires get hotter than others (its not likely they will be evenly heat cycled)
Be sure to try to pick out the tires yourself and use a durometer to measure a few different points on the tire, etc.

Generally its just not a great idea to get used slicks, unless either you just don't care, or you know VERY much what you want and what you are doing.... I have seen this practice of getting used tires go wrong more times than it has gone right... Just be conscientious.

I can understand that, however, I purchase the slicks that have over 3/4 of tread depth remaining. They are rarely used for more than a few sessions/heat cycles, so for 1/3 to 1/4 the price it's absolutely worth it. You can think whatever you want, but I can go through two or three pairs of the slicks and have a lot more fun than a street tire for the same price. The company who sells them hand selects them based on different parameters to make sure that the tires are in as good of shape as new, just with less tread.

I wouldn't be doing it unless the rears were in great shape, which they are. I have not experienced any issues with different heat up points or whatever. I'll keep an eye out for what you're warning me of, but chances are I'll pay $800 less per set of Hoosiers and deal with a little imperfection :tup:

:tup: Sounds good buddy ;) :tiphat: As long as it works for you, that's all that really counts then. :tup:

Not trying to ague with you... just here to help. :)

I buy used R comps myself since a new one is nearly $300. With the economy and tire prices, I plan to only buy one set of new tires a year (RE11). I will buy a set of used R comps later. I don't want to get Hoosiers just yet because I cant fit all four inside the car! I miss the RA1s, but I am not sure how much faster the RA1s are over the RE11, probably less than a second.

Umm, The Toyo RA1's are quite a bit faster than the RE11, easily about 2-4 seconds a lap depending on other variables (even the proposed used RA1's would be at least 1-3 seconds faster than a RE11 depending on how many heat cycles are on the used RA1) .
For one of the best R compounds try the Toyo R888 (replaced the RA1's)

I use Nitto NT01's (similar compound to R888's) and RE-11's and they are considerably faster on track, 2-3 seconds depending on the track layout.

I have used 245/40R18 on the front and 275/35R18 on the rear with excellent results on track days. The selection of tyres in 18" is MUCH better that 19" and the tyre sizes you are suggestion for 18x8 EOM front rim and 18x9" OEM rear rim are truly excessive.

In 18" you have the choice of Advan Neova AD08 as a semi-R spec, or Advan A048, Bridgestone RE55 series, Dunlop DZ series, Toyo R-specs etc. In 19", the choice is more limited.

Going with slight lower sidewall height will drop the CoG of the car, as well as the roll-centres and give you higher cornering limits.

With the standard spring/sway-bar setup of the Z34, I have no difficulty in running a smaller front than rear. If I was to move to bump/rebound adjustable dampers, adjustable sway-bars etc, then it is worth moving to same sized tyes front and rear, but that also implies new rims of identical width.

Maybe 2-3 sec, not sure about 4 sec. Of course it depends on the track. I can tell you my old car was 1-1.5 sec faster on RA1 than Azenis 615 (which had less grip than RE11) on a 1.5 miles course. Heck, A6 was only 1.5 sec faster than AD08 on the same course.

Unlike the R888, RA1 are a lot more consistent and heat cycles don't change it as much. I used to be able to run faster lap times near the end of the tire's life. Heck, I missed the days where I would buy $100 take off RA1s, drive them 600 miles to VIR and track them. I would usually get 3000-5000 miles of street/track/autox use out of them before I have to trash them. If they have it for cheap in the 275/35/18 size, I would probably drive them to VIR instead of the RE11s!

Don't get me started with the R888, they are probably one of the worst tires to buy. They might be faster than RA1 straight out of the box, but they slow down after a few short heat cycles. You could have tread on them, but they are no faster than RE11 by the end of its life. It's not worth the money, especially if you buy take offs. There is a reason why they are bringing back the RA1s.

I recently did a test of R888 vs RE11 at an autox in my car with the same driver. The R888 FELT a lot faster and stable, but the times were the same as the RE11s. They were take offs from race cars that had 3/32nd left on them.

Obviously, these tires are still slow compare to the Hoosiers.