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      01-24-2022, 04:05 PM   #1
DocsF90M5
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Question Upgrading Tires on OEM 20" 789M Wheels

I have a '19 M5C and want to upgrade the OEM tire sizes (front: 275/35R20; rear: 285/35R20). I'm currently running 15mm front spacers and 12mm rear spacers.

What is the widest size setup I can safely run on the 20" 789M wheels?


[Option 1]: front (285/35R20); rear (305/35R20)

[Option 2]: front (285/35R20); rear (295/35R20)

I'll be going Michelin PS4S tires.

Thanks in advance!
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      01-26-2022, 02:33 PM   #2
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      02-04-2022, 03:03 PM   #3
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I'm curious about this also.. Currenlty have the stock 275 (front) and 285 (back) and what spacer needed (or if needed at all) minimum for a wider tires (i.e 285 and 305)
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      02-04-2022, 03:10 PM   #4
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Quote:
Originally Posted by goofym3 View Post
I'm curious about this also.. Currenlty have the stock 275 (front) and 285 (back) and what spacer needed (or if needed at all) minimum for a wider tires (i.e 285 and 305)
Apparently, got more feedback/comments on FB than here (as you can tell lol)!

I was told you can safely run 285/35R20 front and 305/35R20 rear, so that is what I ordered (Michelin PS4S) and will be getting them installed shortly along with powdercoating the OEM 20s.



I'm currently running 15 mm spacers front and 12 mm spacers rear (on the stock setup) and will likely remove them with the new tires.
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      02-04-2022, 03:44 PM   #5
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Look in this thread.

FSHNGRY's 2021 F90M5 Comp Fashion Grey Build Journal https://f90.bimmerpost.com/forums/sh....php?t=1884760
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      02-05-2022, 07:14 AM   #6
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Quote:
Originally Posted by DocsF90M5 View Post
Apparently, got more feedback/comments on FB than here (as you can tell lol)!

I was told you can safely run 285/35R20 front and 305/35R20 rear, so that is what I ordered (Michelin PS4S) and will be getting them installed shortly along with powdercoating the OEM 20s.



I'm currently running 15 mm spacers front and 12 mm spacers rear (on the stock setup) and will likely remove them with the new tires.
There's a reason you got more comments on FB than here. It's because FB is full of more unsafe bullshit than here.

People here are a little reticent to give you advice that might kill you. Not so much there.

That being said, the advice you got appears to be relatively conservative, and may be right. But a few caveats.

1. Every tire manufacturer specifies maximum width of rim in their published information. For the F90, that's 9.5 front and 10.5 (inches) rear. The sizes you quote I THINK are okay for Michelins (but they might not be for others - depends on sidewall, construction, etc.)

2. The front/rear diameter difference needs to be within tolerance for the drive system. I'm not sure the maximum difference is known before a center diff/transmission shits itself. For some drive systems, it's 10% revolutions/mile difference. For some, they quote 0% (but it has to be something other than that, because of tire wear being uneven).

So, sorry nobody answered the original question. Nobody willing to stick their neck out to be an "expert" on potentially bad information, including me.

Shawn
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      05-04-2022, 09:28 AM   #7
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Quote:
Originally Posted by DocsF90M5 View Post
Apparently, got more feedback/comments on FB than here (as you can tell lol)!

I was told you can safely run 285/35R20 front and 305/35R20 rear, so that is what I ordered (Michelin PS4S) and will be getting them installed shortly along with powdercoating the OEM 20s.



I'm currently running 15 mm spacers front and 12 mm spacers rear (on the stock setup) and will likely remove them with the new tires.
howd the install turn out? did the tire shop give you any crap?
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      05-04-2022, 09:41 AM   #8
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Quote:
Originally Posted by Maverik259 View Post
howd the install turn out? did the tire shop give you any crap?
Turned out great! Have about 1K miles since new tire setup and couldn't be happier. I'd definitely recommend this setup.
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      05-04-2022, 07:11 PM   #9
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Can you provide pictures? And pictures parallel to car to see how it looks. Thanks
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