spiral04

I was wondering if anyone here is running a 315 with the Toyo R888's on the stock C5 Z06 rear wheels(18" X 10.5"). Right now I have 295/30/18 in front and 305/35/18 in the rear and would like to go to the 315/35 for HPDE's in the rear. Any thoughts??

Jason
Spiral04

Joy of 6

I'm running 305/35/18 on the stock rims and no problems....

spiral04

That's what I'm running on the rear now and was wondering whether I should, and whether the 315/30/18 would fit?

bobmoore2

A 315 is only 0.4 inches wider than a 305. They will fit.

Joy of 6

You stated that your rear tires were 30 series and mine are 35, so I don't know how the difference between a 305/30 and a 305/35 computes over to a 315 /30. Did I make myself un clear???

longdaddy

why?

spiral04

305/35/18(which I have now) or the 315/35/18 for the rear?? Which will perform better for HPDE's? Also, I was thinking of having a little larger rear tire than the front?

295/30/18 Toyo R888's is what I'm running now up front.

GrantB

Toyo only makes a 315/30/18, and yes they'll fit fine and outperform a 305.

gkmccready

Will they? Everybody is telling me the R888 likes to be stretched to get max performance. 275s on 18x11 for example. 335s on 18x13. 305s on 18x12. Toyo themselves on the website list the 305 overall width as 12.4in and the 315 as 12.5in.

And remember, the 315/30r18 is 25.5in while the 305/35r18 is 26.3in...

spiral04

The 315's only come in a 30 series I believe with the R888's

gkmccready

I'm suggesting you talk to your favorite race tire guy (John@CCW, Ron@AIMTires, etc) before you run off thinking wider rubber is always the best answer. Based on the data on the Toyo website and what I've been told, the only reason for you to go to a 315/30r18 rear tire would be for lower gearing. But I'm just another internet kook, which is why I'd suggest talking to a real tire guy or Corvette shop.

I've been running 295/30r18+305/35r18 R888s on my C6 coupe on 18x11 CCWs front and rear. Which was John@CCWs recommendation... more testing has shown the R888s like to be put on the widest rims possible and we've been thinking of trying 275/35r18 on the 18x11 front, and doing the 305/35r18 on an 18x12 rear. The C6 isn't as happy to accept the wide wheels as the C5 cars. :-(

I guess I'm saying that what fits may not always be what works best. :-)

longdaddy

Wouldn't you get more sidewall flex with 315 tire on the stock 10.5 rear wheel?

This was a problem for me with Nittos - 315 tires would "squirm" under high speed hard braking unless the pressure was just perfect.

I am also having trouble believing that the actual contact patch would be any different once you "maxed out" your wheel width.

spiral04

Something I'll have to check on. I could always put the 295/18's(that I had on the front) onto the rear and add some 275/18's for the front. I'll have to talk with a tire guy!

gkmccready

315/30r18 has 3.7in of sidewall. A 305/35r18 has 4.2in of sidewall. So, I would gather that the 315 in a 30-series is actually going to have less sidewall flex.

You lost me here. Stretching the tire wide is another way of limiting flex. The R888s appear to run wide for the size listed, too.

http://www.toyotires.com/tire/pattern/proxes-r888

Don't believe me... check out the Toyo site. Check out the overall width of the 305/35r18 (12.4in) and the 315/30r18 (12.5in) ... is 0.1in worth it? Probably not unless you want the shorter tire for another reason, right?

spiral04

One of the tires I will be running is the 295 since I already have it. Since my wheels are the same size I can put the 295's in front or back. I need two new tires, now only figuring out what size. I did hear people talking about running 45psi in the tires at the track though??

gkmccready

If it were me, I'd buy another set of 305/35r18 for the rear and keep the 295/30r18 on the front. If you're having no issues with that set up, why not keep running it?

Ron@AIM told me to keep trying higher and higher pressures in the R888s. I used to start at 32psi and now I'm starting at 38psi and there's a lot more grip. I haven't had it out to the track with the higher pressures yet, but if you dig around you'll find folks running 40s hot pressures easy with the R888s.

Last C5

I'm running the 305/35/18 888s on 11" CCWs in the rear at 34 cold and 45-46 hot. Tread wear has been even across the entire tire and handling couldn't be better. My fronts are the 275/40/17 888s on 9.5" CCW, using the same pressures.

spiral04

I've definitely heard alot of people running 45psi hot. I had a used set 0f the 305's, good enough for one track day for me. The 295's were brand new. So I can't say as for performance. The rear did kick out on me at 100+ at Willow. Glad there wasn't a wall!

longdaddy

firstly, i was assuming same ratio, i.e. comparing 305/35 vs 315/35

secondly, here is how my reasoning goes: as you go with a wider tire, same wheel, and the same contact patch, the distance between the rim and where the tire contacts the gound will increase (this assumes that the contact patch is the same size, as should be the case if the same pressures are used). technically, the sidewall section of the unmounted tire will be the same but as you mount wider tire on the same width wheel, you will see sidewall and the edge of the tread surface sort of curve around - I definitely observed this on 315 nittos. this way you will end with a wider (and deformed) section of the tire on the side. I could not imagine that is a good thing and my experience with 315 nittos on the stock wheels seems to support that.

by the way, mounting 315 tire on 10.5 wheel would be more of "compressing" than "stretching"

I bet that toyo's spec assumes that the tire is mounted on the wheel that has optimal width for the tire used, so you cannot make a comparison based on that, if you are mounting either tire on the same wheel.

i don't do tires for a living and i did not go to a tire school, so i may be wrong, but I would like to hear a believable argument if I am

gkmccready

The webpage showed the 305/35r18 and 315/30r18 were both measured on an 11in rim. Like you, I don't do tires for a living, either, but I'm full of opinions and have a pretty good memory for facts and quasi-facts that I hear and read. :-)