[mhammes]

Hello,

I have a 2016 X3 (F25) 35i with Michelin CrossClimate 2 tires. I’d like to purchase a spare tire kit for it for longer trips, but am concerned about compatibility with X-Drive. For example, the Modern Spare kit for the F25 has a rolling diameter of 26.5”. The CC2’s have a diameter of 27.6” (per Michelin’s site and Discount Tire’s sites).

An online chat I had with Modern Spare said that I could use their 18” spare even though I’m running 19” wheels, but said nothing when I mentioned the difference in rolling diameter.
https://modernspare.com/product/2011...e-kit-options/

Bimmerzone’s site comments on it, but doesn’t say anything about it impacting X-Drive.
https://bimmerzone.com/products/bmw-...ncy-spare-tire
“The wheels on my car are 17" (19" or 20"), yours spare tire is 18"?
This is also one of the most common questions. Many get confused with the rim size and outer diameter. The space tires we sell closely matches the outer diameter of the tires on your car (so your car will not ride lob-sided). Of course there is a certain minimum wheel size to clear your brakes, we have determined this in our testing.”

Will the difference between rolling diameters be an issue for X-Drive for a short drive to a repair shop, and if so, how can I disable it? I have seen some threads about X-Drive with lots of conflicting information and opinions.

Thank you for your time!

[Wgosma]

I can’t answer your question but I do know the BMW spec for front to rear tires is maximum variance of 2mm tread depth. That is per the official BMW Technical Information Specs.

Good luck /Bill

[HPR]

The general guideline for AWD tire size mismatch is 1%. This is not a BMW specific spec, but applicable across most modern AWD systems. I believe the 1" plus difference in rolling diameter you cite is way too much. I'd look for something close to or within the 1% margin. Even then, the spare is to get you off the road and to a shop where the tire can be repaired or replaced.

[richardodn]

On the bimmerzone site, their package uses a 165/70/18 wheel with a rolling diameter of 27.1. These are close enough to the stock fitments (~2%) for temporary emergency use. Modern spare uses a T135/80/18 and a 26.5" rolling diameter. I wouldn't use those on an AWD due to the -4% size difference. It would likely be fine for very short drives. However if you're buying these for road trips, you may have to drive a substantial amount to find a replacement for the original. If they could provide that package with a T145/80/18, that would be better.

[richardodn]

I decided to check out various compact spare tires for best 18" fitment compared to the stock 35i 245/50/18 27.6" rolling diameter. Anything I list here will have at least a 99M load rating which is pretty much a minimum.

CONTINENTAL SCONTACT T145/85R18 27.7" 103M +0.4%
GOODYEAR CONVENIENCE SPARE T145/80D18 99M 27.1" -1.8%
MAXXIS SPARE TIRE 165/70D18 116M 27.1" -1.8%

Of these, I'd go with the Continental. It's almost dead on with size and has a load rating sufficient for a loaded vehicle.

[richardodn]

Finally, to really confuse the issue, BMW offers a space saver wheel and tire for the F25 in the parts catalog with the following note:

Not for retail customers, only for
service vehicles and dealer service. No
option for storing spare tire in
vehicle is available.

Guess what size the tire is? Yep. 135/80R18, same as Modern. If it were me, I'd probably try and order the wheel (4.5BX18 ET:-1, PN 36116796147) and buy the Continental separately.