Largest Tire on 8.5 x 19 - The Unofficial BMW M5 Messageboard (m5board.com)

2003 M5!!! · 1st July 2004, 06:43

Hi guys,

I just wanted to make sure that I am using the largest tire I can on my 8.5 fronts (which are 19) that are on back order until the 7th. I like a little beefier look (of the tire) so would like to go a little larger than 245/35, but don't know how far I can go.

Thanks in advance. I also know that some people have done 9.5s in front, but I am concerned that I would be the "one" that had rubbing issues . . . .
so I stuck with 8.5s.

Thanks!

ELEVENS · 1st July 2004, 22:49

Michelin specifies a minimum of 8" wheel for 245's, 8.5" for 255, and 9" for 265's. A wider wheel will help prevent the tire from folding/rolling under with high lateral loads (tossing it into a corner!).

I have 8.5" on the front, and if I were to do it again, I'd go with 9". That's what the Dinan's are, and (at least theoretically) should perform better, with no rubbing. I went with 10's on the rear with stock tire sizes, so 1/2" wider all around (stock is 8" up front and 9.5" out back).

Good luck and have fun!

2003 M5!!! · 1st July 2004, 23:36

Thanks!

The problem with the SSR GT3s is that I must use either 8.5s or 9.5s in front. I think I will stick with the 8.5s with a 245 or 255. I am concerned that the 9.5s will be too much.

I cannot wait to get them! They are on back order until next month

Quote:

Originally Posted by ELEVENS

Michelin specifies a minimum of 8" wheel for 245's, 8.5" for 255, and 9" for 265's. A wider wheel will help prevent the tire from folding/rolling under with high lateral loads (tossing it into a corner!).

I have 8.5" on the front, and if I were to do it again, I'd go with 9". That's what the Dinan's are, and (at least theoretically) should perform better, with no rubbing. I went with 10's on the rear with stock tire sizes, so 1/2" wider all around (stock is 8" up front and 9.5" out back).

Good luck and have fun!

gsfent · 2nd July 2004, 01:07

Quote:

Originally Posted by 2003 M5!!!

Thanks!

The problem with the SSR GT3s is that I must use either 8.5s or 9.5s in front. I think I will stick with the 8.5s with a 245 or 255. I am concerned that the 9.5s will be too much.

Why do you think 9.5 is too wide in the front?? A lot of folks have put stock 9.5's on the front using 3mm spaer. If you can get custom sizing, just add3mm to the standard backspacing to move the wheel out slightly and you will have the right offset. Or get stock backspacing and use the 3mm spacer that Luke@ Tire Rack sells.
Regards,
Jerry

M5Kid · 2nd July 2004, 02:22

Would I be correct in saying it's not so much how wide the wheel is upfront, rather the tire? A good example is Jason's new setup with 8.5" BBS CH's upfront shod with 275/30's. It's a whole inch narrower wheel than guys who run stock rears upfront, but it's the same tire width. Bottom line is, the tire is what will be in contact with the fender liner, not the wheel, so concentrate on tire width's rather than wheel widths.

Can somebody tell me if this is a correct statement, I hate to be throwing around false information.

Thanks,

Travis

ELEVENS · 2nd July 2004, 05:35

Quote:

Originally Posted by M5Kid

Would I be correct in saying it's not so much how wide the wheel is upfront, rather the tire? A good example is Jason's new setup with 8.5" BBS RC's upfront shod with 275/30's. It's a whole inch narrower wheel than guys who run stock rears upfront, but it's the same tire width. Bottom line is, the tire is what will be in contact with the fender liner, not the wheel, so concentrate on tire width's rather than wheel widths.

Can somebody tell me if this is a correct statement, I hate to be throwing around false information.

Thanks,

Travis

Travis,

Tire width and section width can be confusing. Tire width is the first number in what is written on the tire, such as 245/40-18. Section width is the actual (measured) width on a certain -sized wheel.

Basically what this means is that the width of the wheel impacts how wide your tire will actually measure. Manufacturers usually cite the section width on a specified-width wheel.

For example, a stock rear Michelin 275/35ZR-18 has a section width of 10.7" on an 9.5" wheel. Michelin further states that section width changes approximately 0.2" (5mm) for every 0.5" change of rim width.

So with my 0.5" larger rims, I have effectively increased my stock tire size from 275 to 280 in the rear, and from 245 to 250 in front. And the beautiful Dinan 9" front rim would make a stock 245 tire measure as though it was a 255.

Hope this helps.

M5Kid · 2nd July 2004, 06:57

ELEVENS,

Thanks, that really cleared some things up, and is interesting info! Let me fire off another question at you. I understand that the second number in a tire measurement is the aspect ratio, which relates directly to sidwall height. Here is my question, is the sidewall height the same on a 235/30 tire as it would be on a 285/30 because the aspect ratio number is the same?

Thanks,

Travis

ELEVENS · 2nd July 2004, 14:06

Quote:

Originally Posted by M5Kid

...I understand that the second number in a tire measurement is the aspect ratio, which relates directly to sidwall height. Here is my question, is the sidewall height the same on a 235/30 tire as it would be on a 285/30 because the aspect ratio number is the same...

Nope. The aspect ratio is simply a percentage of the first number (width). In your examples:

235 x 0.30 = 70.5mm sidewall height.
285 x 0.30 = 85.5mm sidewall height.

Aspect ratio is a useful "tool" to adjust tire height and rolling circumference. On the beast, with 245/40 on the front and 275/35 on the back, both are about 25.7" tall thanks to different aspect ratios, despite the rears being much wider.

BostonRocket · 2nd July 2004, 19:50

I have 255 Michelins on my 8.5" SSR fronts. No rubbing at all. I even have an aftermarket suspension.

'Rocket