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  1. #1
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    Default Questions on Tire Sizes for a 10.5 Wide Wheel

    My new wheels showed up a couple days ago, and I finished up changing the lower control arms and tire rods over to SN95 99-04 parts to better work with the 10.5 wide wheels. Still not sure on spacers, if they are needed, and what size. I think that is going to be influenced by tires.

    Concerning tires, I had initially planned to run a 315/30-18 BFG Rival S on each corner of the car. It's not really built as a track car, so the 200 wear is more than I need most of the time. Someone that runs in the Optima series suggested I drop down to a 285 Bridgestone Potenza RE-71 as the 315 "will feel sloppy" with anything less than 450 rwhp.

    The car will run a 2.73 rear gear this year and will eventually go to a 3.55 to stay a little more highway than city driving with the T5 transmission. Springs will be changed next Winter, and I'm not overly concerned with a 200 wear rating on the tires. It's a hobby car.

    What do you think between the 285 or the 315? Does it really matter if it's just a hobby car? Will the 315 make the car so unbearable?

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  2. #2
    Moderator wraithracing's Avatar
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    I am not sure how your HP rating will cause the tires to feel "sloppy" or not.

    I can see how the 285 compared to a 315 might feel tighter due to the 285 being a bit narrower and stretched just a bit to fit the 10.5" width. Where the 315 is stretched less to fit the same width. Pretty standard practice for competition vehicles to run a tire that is either the same basic width or even just a bit narrower than the wheel width to you have less "slop" or sidewall roll over when cornering at high speeds etc.

    So in a competition sense the 285 might be a better choice. As for street driving I don't see much difference other than the 315 being heavier might cause you to be a bit slower and get less fuel mileage. The 285 might be a cheaper option so that never hurts. Obviously a 285 will fit easier or better than a 315, but with your 3" flares neither should give you any issues.

    I would say buy what fits your budget, your plans, and/or what you like. Either should work just fine for what you plan. Once you start competing there will be other considerations in regards to your tires besides just the sizing. Good Luck!
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  3. #3
    FEP Senior Member Patrick Olsen's Avatar
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    Quote Originally Posted by wraithracing View Post
    I am not sure how your HP rating will cause the tires to feel "sloppy" or not.
    I agree - "the 315 'will feel sloppy' with anything less than 450 rwhp" just strikes me as bench-racing nonsense. FWIW, I have 315/30-18 615Ks on 18x10.5"s on the rear of my car and I haven't noticed any sloppiness despite my only having ~380rwhp. Maybe my butt dyno isn't calibrated finely enough.

    Quote Originally Posted by wraithracing View Post
    I would say buy what fits your budget, your plans, and/or what you like. Either should work just fine for what you plan. Once you start competing there will be other considerations in regards to your tires besides just the sizing. Good Luck!
    I agree with all that, too.
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  4. #4
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    Quote Originally Posted by Patrick Olsen View Post
    I have 315/30-18 615Ks on 18x10.5"s on the rear of my car
    Any reason to choose the Falken over the BFG? Falkens are a little more expensive, which is why I was thinking BFG. Same tread wear rating, and I won't probably notice any difference with mine.
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  5. #5
    FEP Senior Member Patrick Olsen's Avatar
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    Pricing may have moved around a bit, I'm fairly certain I would've gone with whatever was cheapest at the time, since it's just seeing street duty. And I may have the older RT615s rather than the newer RT615Ks, I honestly don't recall.

  6. #6
    FEP Senior Member BMW Rider's Avatar
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    Quote Originally Posted by wraithracing View Post

    I can see how the 285 compared to a 315 might feel tighter due to the 285 being a bit narrower and stretched just a bit to fit the 10.5" width. Where the 315 is stretched less to fit the same width. Pretty standard practice for competition vehicles to run a tire that is either the same basic width or even just a bit narrower than the wheel width to you have less "slop" or sidewall roll over when cornering at high speeds etc.
    This was the determining factor in how I chose my tire sizes. Although I'm not running nearly as wide of tires, I went with the sizes that were the optimal fit for my wheels to minimize the side wall roll. I'm pretty sure I could go up a size or two without much if any rubbing, but I went for the performance not just the looks. I did go with the RE71Rs after looking at a lot of different tires and the reviews and ratings of them all. They are rated as the gold standard in autocross tires and everything else seemed to be compared against them.

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