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BMW e30 w/RS4 245s on TRM 15x8?


frankrehnelt
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46 minutes ago, frankrehnelt said:

We are looking to go ahead and switch from RS4 225 on 15x7 to 245s on TRM 15x8s. Any experience out there and advise anyone would like to share? 

 

Thanks y'all, Frank

901 Motorsport 

@Hi_Im_Will did a big write up last year about what size (width) rims that these 200 treadwear tires work best on.

See if you can find that post.

For 245's the recommendation is 9.5 to 10" wide, although a lot of folks run them on 9" wide rims. 8" is correct for a 225, but too narrow for a 245.

 

Edited by mcoppola
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My 2 Cents, I've always thought there was better transient response while turning with a tire that was fitted to the higher end of it's recommended width range, and there is plenty of science and real world tire tests to back that theory up. This is not to say you can't go too far like the JDM stretch scene.

 

Not very scientific, but I always go on tire-rack and look at the recommended width range for a given tire's specifications, and try to stay within a half inch of the upper end for any autocross/track car.

 

YMMV

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I sort of think of this the other way around, and maybe this is what Rob is getting at. Either way Rob and I both follow the 225 ish thought for 8"

 

Pick the tire you wanna run, buy the rims that best fit that tire. If you can get 245's, they do best in the 9 to 10" rim range. If you can or only want to pay for 225s (more availability) get a 7 to 8 in rim. 

 

I would guess a 8" rim with 225 and 245 would be pretty close, and would thus be sort of a waste of the extra cost and difficulty in finding a 245. 

 

Of course I buy cheap rims so I can change my mind (and my drivers tend to use them as curb feelers) as tire availability changes. 

Edited by Black Magic
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18 minutes ago, Black Magic said:

I sort of think of this the other way around, and maybe this is what Rob is getting at. Either way Rob and I both follow the 225 ish thought for 8"

 

Pick the tire you wanna run, buy the rims that best fit that tire. If you can get 245's, they do best in the 9 to 10" rim range. If you can or only want to pay for 225s (more availability) get a 7 to 8 in rim. 

 

I would guess a 8" rim with 225 and 245 would be pretty close, and would thus be sort of a waste of the extra cost and difficulty in finding a 245. 

 

Of course I buy cheap rims so I can change my mind (and my drivers tend to use them as curb feelers) as tire availability changes. 

Yep! 

 

We buy cheap rims too!  It is EASY to get 15 x 8 or larger with used jeep wheels...

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I'd have to search for the post/document, but some Spec Miatas did some testing a few years back that showed a small amount of stretch produces the best lap times. IIRC it was a ~1s per lap on a ~1:20 track for 225s going from 7" to 8", and another ~1s from 8" to 9".

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