May 29, 2020, 03:09:36 am


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285mm on 9"

Started by TheFrankenberry, July 14, 2017, 12:48:21 am

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So I just picked up pristine factory SRT8 forged Alcoas for a steal. These are 20x9" wheels rather than my 20x8" daily stockers or 18x8" winter/autox wheels.

Looking at the scarce 20" RE71R selection there is a 255 option but that's only 10mm larger than the 245/45R18 that I run now. There's also a 285/35R20 option but the approved rim width is 9.5-11" (and that goes for all the other manufacturers with a tire in that size as well).

Searching around online brings up a consensus that a half inch difference is fine (including use in HPDE) but some caution about pinching and compromised sidewall strength. That latter bit concerns me slightly with my 4000lb machine, but the load rating of the 285/35R20 RE71R is actually greater than the OEM tires.

Thoughts on a 285mm tire on a 0.5" undersized rim? Seeing the Mustangs and Camaros with 305s on 19" wheels have me wishing hard for wider meats on my pig.
2010 Dodge Challenger R/T (#345)
in Furious Fuchsia w/ li'l 345 cid Hemi


Safe? Yes. Best performance? I can't say as I don't know 20s. A 285 is a bit wide for that wheel and would be best suited on a 10-10.5 wheel
Ron Williams
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I think Dan uses a 275 on a 9" wheel in his Mustang.
Alex A.

Steel Cities Region AutoX Chair
Current: 2016 Subaru WRX STI - 77 BS
History: 2008 VW GTI - 1 SMFT, 2003 BMW M3 - 77 STU


FWIW, I had 275s mounted on 9.5's and they fit pretty well. I was about to put 285's on them and expected a little pinch, but anticipated that they would be worth it.

Stock Mustang GT wheel width is all over the place, but it doesn't look like they go above 9". Prrretty sure Dan had a square 275 setup with what looked like no pinch.

This is what 265's looked like on 8.5". There was a little pinch. I would expect 285's on 9" to be just a little more than this. Which I would do.
Nick Phillips
Steel Cities Region AutoX Chair
Past: 2011 E92 M3, 2008 GTI
Present: N/A
Future: 'Murica


Yes, I have 275's on my 9 inch wheels and they are a tad pinched, certainly more so than the factory 255's.  I think Chad Englert, who drives the grabber blue Mustang with orange STP...runs 285's on factory 9 inch wheels, so I know those are possible.  They do seem noticeably pinched, but nothing I would worry over.  However, my mechanic bitches and moans about having to mount those wheels every time I ask him to do so.  I still think that's more due to the sidewall of RE-71R's being so stiff than the tire being pinched.

As far as Mustang wheel sizes go, the track package from my vintage comes with 19x9's all around.  Newer ones run staggered setups with 9.5's in the rear.
"He who shall be last, shall be sideways and smiling."
- Jezza 19:3

2014 Ford Mustang GT #10 FS
1999 Mazda Miata #10 ES
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I saved pics from some guys running 285s on 9" rims on the Mopar forums and it doesn't look bad at all. Certainly not as bad as other rubber I've found guys trying to squeeze onto the rears. Unfortunately, the individuals I've contacted running 285s did it for looks and never abused them.

I know they fit and the consequences wouldn't be catastrophic (especially since I always have my daily rubber that I swap at the track). I'll still keep pestering Bridgestone to bring out the RE71R in 275/40R20 though. Thanks for the input fellas.
2010 Dodge Challenger R/T (#345)
in Furious Fuchsia w/ li'l 345 cid Hemi


I have 255's on 7.5 and they aren't really pinched. I used to run 285's on 7.5 when I ran hoosiers. of course I am the bigger is better person
Trevor D Hill Sr.
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