[matowi]

Makes me wonder how BMW in different markets approaches the tire size matter. First thing that’d happen if I showed up at a dealer for service with non-OEM tire size: voided warranty. They’d immediately hop on me saying the tires will create too much tension, or whatever forces which will lead to increased wear and tear on the x-drive components, and so on

I heard this warning so many times with my prior 3 BMWs that I’d never consider putting on any tires in sizes varying from the OEM specifications

Some dealers would go as far as saying that you lose warranty when you put on tires without the BMW star marking, even if the said tires meet OEM size requirements

My head swells in amazement every time I see a thread discussing how well your cars perform on whatever tires you dream up

[mojoJJ]

Well, if you look at the specs of the OEM 22” tires, they have the same 0.7% (3 revs/mile) difference in diameter between the front and rear tires as the 21” Michelin tires being discussed here. Although, in the 22” OEM setup the front tire is larger whereas in Michelin 21” the rear is larger. But that shouldn’t make a difference to the xDrive system or the drivetrain. So technically even if BMW denies warranty on drivetrain because of this, you could always argue that 22” OEM setup has same size difference.

[slicky]

The screen shot above misses an important point that star tires are not going to be the same diameter as non star tires of the same size. They could be either larger or smaller to provide a perfect match front to back. Designed as a matching set. This is why BMW wants you to use star tires. You are not going to have a 0.7% missmatch with them.

[mojoJJ]

Originally Posted by slicky

The screen shot above misses an important point that star tires are not going to be the same diameter as non star tires of the same size. They could be either larger or smaller to provide a perfect match front to back. Designed as a matching set. This is why BMW wants you to use star tires. You are not going to have a 0.7% missmatch with them.

The tire size (including diameter) is defined by the three numbers above, the “star” has nothing to do with that. What might vary (and missing from the discussion here) is the load index and the speed rating, which has nothing to do with xDrive system.

[matowi]

Well, what I see in this picture is that the taller 21” wheels are over 1 inch bigger in diameter than the OEM specified 22” wheels

In my post above this was the factor I was referring to — the wheels don’t meet the diameter limit set by OEM. Consequently, showing up to a BMW dealer/authorized service shop with such wheels would void my warranty on the spot. Greater wheel size translates to greater weight, and that adds whatever forces which may impact whatever components of x-drive or other parts of the drivetrain. At least that’s the spiel I heard so many times

On the star marked tires: they are manufactured in such a way that the difference between rear and front are (close to) eliminated, as stated in another post above

[slicky]

Originally Posted by mojoJJ

The tire size (including diameter) is defined by the three numbers above, the “star” has nothing to do with that. What might vary (and missing from the discussion here) is the load index and the speed rating, which has nothing to do with xDrive system.

This is incorrect. Star rated tires are not going to be the same size as non star tires. BMW specifies the compounds as well as the size, which may and does deviate from the theoretical diameter defined by the width/aspect ratio/wheel diameter for 21" X5 wheel application. Star rated 275/35/21 and 315/35/21 tires are exactly the same diameter. Non star rated 275/35/21 and 315/35/21 tires are not the same diamter. Non star rated tires will absolutely result in additional slippage and wear in the transfer case. How much more? No idea.
This is just the kind of bs we have to deal with with an xdrive staggered setup. If I knew it when buying our X5, would have excluded with the 21" staggered tires or the xdrive 40i and bought the sdrive 40i. Its a fn nightmare.

[mojoJJ]

Originally Posted by slicky

This is incorrect. Star rated tires are not going to be the same size as non star tires. BMW specifies the compounds as well as the size, which may and does deviate from the theoretical diameter defined by the width/aspect ratio/wheel diameter for 21" X5 wheel application. Star rated 275/35/21 and 315/35/21 tires are exactly the same diameter. Non star rated 275/35/21 and 315/35/21 tires are not the same diamter. Non star rated tires will absolutely result in additional slippage and wear in the transfer case. How much more? No idea.

Is there a conclusive evidence to this? I understand that star rated tires might have much tighter tolerances which might lead to “closer” matching in diameter vs non-star rated tires on extreme ends of respective tolerances. But saying that star rated tires have different diameters vs standard tires? Why have the tire size stamped at all? Wouldn’t this goes against the tire sizing convention?

[TexasBimmer89]

Just had a set installed on my wife’s X5. It will be nice to not have to look at daily temps during the winter before driving.