[Milestune]

Hi,

I have a 2011 550XI and the summer wheels (19") have 3 almost new tires 8/32, and one 5/32.....

Is the Xdrive OK with this?

[.BMW.]

When front and rear tire diameters are discussed for xDrive 1% is often used as limit.

1% translated into thread depth would result in around 5/32".

I think that your difference of 3/32" would be ok.

[PJinCA]

If you look at the sidewall of your tires there are little triangles along the outer edge of the sidewall, these are one of the wear indicators the tires come with. The other wear indicator is the wear bars that run across the tread of the tire, these are located between the tread. Once the tire wears to those wear bars it needs to be replaced.

https://www.rightturn.com/tire-guide/tire-wear-bar/

[Errowen]

Originally Posted by .BMW.

When front and rear tire diameters are discussed for xDrive 1% is often used as limit.

1% translated into thread depth would result in around 5/32".

I think that your difference of 3/32" would be ok.

I think this advice is based on bad math and the suggestion you can go to a 5/32nds spread between the tires is not supportable.

.BMW states BMW recommends no more than 1% difference. I haven't been able to confirm that number, but if we accept it, the 1% is a reference to circumference. What counts in terms of wear and tear on the AWD components is the difference in the number of wheel revolutions per mile absorbed in the viscous couplings. When you take your xDrive in with codes for an overheating transmission or other driveline components, the technician checks tire circumferences, not tread depth.

AWD couplings are designed to cope with intermittent differences in tire travel on corners; they are not designed to absorb continuous torque without a cooldown, which is the result of long distance travel with tires with different circumferences. The couplings will overheat and fail, and I'm saying that from personal experience with an AWD Jeep Grand Cherokee, which when the whole driveline locked up, had a one inch difference in tire circumference front to back due to increased wear on the front from steering and braking.

A 245/40R19 tire on an F10, when new, has a diameter of 679 mm and a circumference of 2,133 mm. A 1% difference in circumference is about 21 mm. The corresponding difference in diameter is 673 mm, or 3 mm of tread depth on each side of the tire. That corresponds to 4/32nds in tread depth, not 5. That 1/32nd counts! BTW, Tire Rack's recommendation is no more than 3/32nds difference for AWD's generally (also VW's and Audi's recommendation), and 2/32nds for Subaru.

It is difficult to predict how quickly the spread in tread depth between your four tires is going to increase another mm (assuming max 1% difference in circumference is the correct measure), but it's so close to the limit, it has to be contributing excess driveline wear. I wouldn't run it.

[.BMW.]

Originally Posted by Errowen

I think this advice is based on bad math and the suggestion you can go to a 5/32nds spread between the tires is not supportable.

I don't think my math is that bad, maybe I should have round off to 4/32" instead. But OPs tires are still within the diameter difference offered by BMW from factory.

Lets compare two staggered tire combos offered by BMW for xDrive F10.

OEM staggered 19" setup:
F: 245/40-19, 679 mm
R: 275/35-19, 675 mm
The diameter differs by 4 mm which is 2 mm or about 3/32" per tread.

OEM staggered 20" setup:
F: 245/35-20, 680 mm
R: 275/30-20, 674 mm
The diameter differs by 6 mm which is 3 mm or about 4/32" per tread.

[Milestune]

Great info guys, thanks! Let me ask you this.. As the OP stated, I have ONE tire that is worn, the other 3 are almost full tread depth. Does the 4/32 difference come into play when we're talking front to back, or is it fair play when we're talking just ONE is 4/32 different?

[Errowen]

Originally Posted by .BMW.

I don't think my math is that bad, maybe I should have round off to 4/32" instead. But OPs tires are still within the diameter difference offered by BMW from factory...

Good points. It would be great if BMW actually published some parameters on this significant driveline wear factor -- I haven't been able to find anything.