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Discussion Starter #1
It looks like we have a new wheel manufacturer to cater to our wishes... Forgestar seems willing to provide us what we want. I hope that this post will begin to answer some questions that a few Autocrossers would like the answers to. If we do get those answers it will be from the people that went out to the extreme and learned from hard knocks, and $$$ spent. I'm hoping they will share their lessons with us... I have run 295-30-18 A6's on eight inch rims with no problems/ both the SSR & OZ rims but as soon as you step out of this... things change fast even the 9 inch OZ and questions start being asked about interference issues... more on that later... so we are talking about Autocross issues here ... NOT Street Cars... only a very few have tried to run 315-30-A6's and it is being done... so to start this out right... If what you know now... what you wished you knew then... what optimized wheel width & offset would you have started with trying to run the 315-A6?... and it looks like the first thing you have to do is roll your rear fenders...Please no street questions here... Dr. Jones? Shabby... others? ...SSR Type C-RS 18x8 ET55 18.4lbs/wheel $489 each

OZ Racing Ultraleggera 18x8 ET50 18.4lbs/wheel $325 each... Can't find the OZ 18-9 no longer available.
Custom rims, wheel tire packages for your ride - RIMSnTIRES.com
Thanks
 

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Some of the things i noticed with 315's on 11" +50 rims is that you can't go full lock with the steering wheel, the tire will rub near the top of the shock bracket, a bit of an annoyance in certain parking area's at events.
Ride height can't be too low either since the rear tires will rub no matter what.
Other than that the grip is just nuts.
 

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Discussion Starter #8
Thanks

This post is about fitment, so using an 11 width you add a 1" spacer in the back and whatever OS and you can swap front to back with some rubbing here and there but it is being done... of course if you are going to use a 315 tire you would want to maximize the traction available by using the optimum wheel width... IN A PERFECT WORLD... but for fitment and maybe just for thought practice lets consider these facts. The C/S Sol uses an 8" rim and a 285 tire , the A/S Sol uses an 8" and a 295 tire... obviously neither of these sound that great but they actually work quite well... looking at this...
46840 P285/30ZR18 E 10.9" 24.9" 78.1" 10-11" 10.0" 11.5" X X
46843 P295/30ZR18 E 10.8" 25.3" 79.5" 9.5-11" 10.0" 11.6" X X
46846 P315/30ZR18 E 11.8" 25.6" 80.5" 11-12" 11.0" 12.5"
the 315 is aproximatly 1" wider than the 295 so could you pinch a 315 onto a 1" wider wheel than you can a 295 and that would be a 9" wheel and now we have the option of 9.5's and 10.'s I wonder if there might be a sweet spot in there somewhere... this to me is not about competition but more of a fun Time only car... like maybe some Forgestar's and some Avon's or some custom wheels and some Goodyears... It's all about fitment Thanks again... RV
 

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so could you pinch a 315 onto a 1" wider wheel than you can a 295 and that would be a 9" wheel
Sure you can, but the contact patch of the 315 tire will be around 295 at best on a 9" rim. If you're getting new rims might as well get properly sized rims for the tire, also i doubt avon's will fit as easily on a smaller rim as the hoosiers usually do.
 

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The hoosiers were the only oversize tires (to wheel width) put on the sol that I'm aware of. Hoosiers are known for very soft sidewalls and thus made doing that possible. People did it to stay in the stock class and maximize tire width. Still it was a compromise because the footprint is squeezed and tires won't work as well as when on properly sized rims, as shabby noted. I seem to remember Shabby had the Hoosier 295's on the stock wheels, and then wider wheels. And you commented on how much better they worked on the wider wheels. Maybe I'm wrong though...
 

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Discussion Starter #11
Again...

Fitment Issues... P295/30ZR18 E 10.8" 25.3" 79.5" 9.5-11" 10.0" 11.6"
The manufacturers wheel width recommendation is ??? I am not trying to be controversial... but it seems everyone but me agrees that 11"is the right size for the 315 and they are right... or are they? on what car? I think fitment issues play a larger role when we are talking about the Kappa... read the posts with an 11" wheel you rub in the front and you rub in the back and you gotta run spacers... I'm still looking at and crunching #?'s but I don't see anyone else out here... I think Sky888 bought some 10" Forgestars but for a street tire setup Your thoughts are welcome and appreciated
 

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Among seemingly a thousand different things we have going on, we have been slowly prepping our manual 2009 GXP Coupe for the track. Ordered and installed the DDM braces front and rear. Next up were the Brembo calipers and corresponding larger front rotors. Then, of course the OEM wheel no longer fit so rather than a spacer, I ordered a single Enkei PF01 18 x 8 to see if it would clear the caliper. It did, so we ordered 3 more. We have been using the Hankook RS3 with great results on our other track cars but I waited for a month to get a size I wanted for the Enkeis but they never came in. So, ordered up some Bridgestone RE11's and got them right away. I too debated and debated the size trade-offs. Eventually I decided for a 265/40-18. We do our own mounting and balancing and I can tel you that these stiff sidewall 265's were tough to get onto the 8" rim. Also, they are just on the edge of looking a little bit funky because they are showing that "pulled in" look. I'm glad I didn't try anything wider and I am not convinced that wider is necessarily better. We'll make that determination after we start dialing it a little bit at Spring Mountain. Next up was sway bars. I ordered those from GMPP and just installed them yesterday. The front bar was a piece of cake, but the rear bar was easier with the exhaust removed. So now the rear bar is on and the exhaust is laying on the floor..... and I'm wondering if I put it back on or just order the Magnaflow - lol. Oh, and since I have digressed this far, the first mod we did to the car was the tune upgrade and OMG!! this was night and day. After acquiring the car we SERIOUSLY wondered about it's lack of engine performance but the tune was an un-real turn-around for us. All of a sudden it was viable.

OK, back to the subject at hand. IMHO and limited experience, squeezing anything larger than a 265 on an 8" rim - well, good luck. It will take some effort and based on the way my 265's look, a 275-315 is going to look bizarre on this small of a rim.
 
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