315 front tire and wheel question

[ACRBruce]

Anyone running 315 front tires out there? I'm running 305 Kumho V700 fronts and the tire is sticking out as far as I want it to go but am thinking of getting another set of tires/wheels for the street w/ 315 fronts as the tire I want to try, the Kumho XS only comes with 315 in 18" size. For those running 315's, what wheel offset are you running? I'm thinking of going down to a +55mm offset, instead of the OEM's +50mm to pull the outside tire shoulders back in a bit. Any opinions?

 

[Vypr Phil]

Bruce, I would give Mark J. a call at Woodhouse.

He is quite the expert on these issues and speaks from experience.

He also has a lot of alignment settings data and specs for special installations like the one you describe.

Phil

 

[j-rho]

Bruce, I run a 315/30-18 Hoosier up front on stock width wheels, which have 1/4" less offset than stock. Sort of the opposite direction you're thinking of going. They fit fine, though my car is a non-ACR at stock ride height. I'll be going to 335's next.

If you're on stock-width wheels, you'll have plenty of room to go inboard. If you're on 11's or 12's you'll start to lose steering lock at some point, if that matters to you.

 

[ACRBruce]

Bruce, I run a 315/30-18 Hoosier up front on stock width wheels, which have 1/4" less offset than stock. Sort of the opposite direction you're thinking of going. They fit fine, though my car is a non-ACR at stock ride height. I'll be going to 335's next.

If you're on stock-width wheels, you'll have plenty of room to go inboard. If you're on 11's or 12's you'll start to lose steering lock at some point, if that matters to you.

Hoosiers tend to run 2 sizes wider than normal tires so do your 315's shoulder roll over on 10" stock width wheels? For the Kumho XS that I want to run, the wheel for 315mm tire s/b 12" wide and that's why I'm thinking of ditching the stock wheels. What wheels are you going to run for the 335 fronts?

 

[j-rho]

The 315's are pinched a little bit on the 10" wheels. Unfortunately the class I race in (SCCA Solo's Super Stock) limits me to stock width wheels, so I'll have to use them with the 335's also. The wear pattern is actually pretty good though with a big front swaybar and max'd out camber.

Were I not limited in wheel size, I would probably run 12" or 12.5" front wheels, since I don't care about turning to full lock. I would recommend talking to John Purner at CCW (Complete Custom Wheel), he probably has a better idea of what backspacing is reasonable, having sold tons of custom race wheels for Vipers.

 

[gb66gth]

I was talking with some of the guys during the Viper Days final at ECR, and they were saying that even a 315, on a stock size wheel won't rub

 

[Grant]

CCW should be able to get you a wheel package for $2900 to $3000 for those size XSs. After talking with John, I decided anodized black (they also do powder coating) SP16Rs in 18x11.5 and 19x13 would be best for my application. I am not sure if he has a 18x12 front wheel that can be matched with a 19x13 rear. For racing use he mostly sells 18" wheels all the way around.

j-rho, Kumho's wheel width range is 10.5 to 11.5. Think its a good idea to run a 12 or 12.5" wheel (admittedly, their 345 range only goes up to 12.5")? The XS's section width is actually wider than the R6's: 12.6" vs. 12.5".

 

[j-rho]

I'm pretty sure John can make the SP16 in 18x12. What he doesn't offer is the "Classics" in 19" diameter, which is too bad, that's my favorite CCW.

I don't know about the Kumho XS, but in my experience, for cornering, tires almost always perform their best when given a wheel a little bit bigger than the large side of the recommended range - especially up front. I ran the 315/30-18 A6 on a 12.5" wheel on my last race car, worked great.

When I move to a class with unlimited wheel widths I'll be using 335/30-18 on a 12.5" up front and 345/35-18 on 18x14 rear. That's for autox though.

 

[Viper X]

Bruce,

I ran Hoosier R6s in 315 x 30 x 18 on SSR's (OE offset) on the front of my 2006 coupe at Fontana the day that you were Auto Crossing. They worked very, very well along with the 335 x 30 x 18 rears.

I just bought a set of PS2's in 315 x 30 x 18 for the front of my ACR. I plan to run them as rain tires on the track and on the street from time to time. They'll be mounted on 18 x 11 Forgelines. Be careful with offset as it's pretty important with the larger tires (like 315's up front). There just isn't that much room inside the fender on the front of the SRTs. I'd stay as close to stock offset as possible and increase your front spring rate or increase the ride height and stiffen the front shocks as well.

The rears will be 335 x 30 x 18 PS2's on 18 x 13 Forgelines.

Another friend with an ACR (track guy not AutoX) has run 315 x 30 x 18 Hoosiers on his OE 18 x 10 inch front wheels and claims that they fit and work very well. Tire temps and wear patterns were OK too on the track.

I think they'd be a bit "pinched" as stated above and would not run them that way, but that's just my opinion.

I also plan to run 315 fronts & 335 rears, Hoosiers, both 18's on the track.

I'm not an Auto crosser, so I don't know that world very well. Maybe extra wide wheels work better at the lower speeds of an Auto Cross event.

I would not run extra wide wheels on a race track though. You want the sidewall working with you, so correct wheel width is important at speed.

Good luck,

Dan

 

[ACRBruce]

The 315's are pinched a little bit on the 10" wheels. Unfortunately the class I race in (SCCA Solo's Super Stock) limits me to stock width wheels, so I'll have to use them with the 335's also. The wear pattern is actually pretty good though with a big front swaybar and max'd out camber.

Were I not limited in wheel size, I would probably run 12" or 12.5" front wheels, since I don't care about turning to full lock. I would recommend talking to John Purner at CCW (Complete Custom Wheel), he probably has a better idea of what backspacing is reasonable, having sold tons of custom race wheels for Vipers.

Do you happen to have a picuture of how the 315's look on the stock 10" rim? I ran 275 NT01's on my EVO's 9" rim and not only the tire looked pinched, and one day at the track, the tire's shoulder was all be gone but the EVO pushed like carzy, even with front camber plates set to the max.

 

[j-rho]

Would certainly be better on a 2" wider wheel, but still in the realm of OK for us wheel-width-limited folks.

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[ACRBruce]

Would certainly be better on a 2" wider wheel, but still in the realm of OK for us wheel-width-limited folks.

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Wow, the sidewall does stick out beyond the fender quite a bit. Perfectly fine for the autox but probably too much for the street so I think I won't run the 315's on stock rims, will have to look for aftermarket rims w/ at least +55 or more offset.