Quote:
Originally Posted by brad850csi
Quote:
Originally Posted by Miko M
Are you saying front 20" and rear 21"????
You can't do that on this car!!!
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Sure you can. BMW allow you to do square tyres as well as one of the options being 265/40r19 with 285/40r19.
So from identical circumference front and rear up to 2.3% bigger at the rear.
Running 275/35r20 and 295/30r21 is only 1.4% different and 275/35r20 and 305/30r21 is 2.2% different |
265 front and 285 back is 2.6%. NOT 2.3%
Didn't know we have that size, all I know is 275 front and 285 back which is 1.1 %
Bmw recommendation is 1.3% or less
Obviously less is better.
Rim width doesn't effect the rolling diameter much but, you can't stretch the tire to much.
This is old article from BMW :
"The tire circumference can fluctuate up to 1% or more as a result of mixed tires or wear. The tire tolerance logic decides depending on the driver's command and driving situation whether the slip is to occur in the transfer case clutch or at the contact area between tire and road.
If the slip is permitted in the transfer case clutch, the locking pressure set by the pre-con- trol is reduced in order to keep the work loss low. In the driving dynamic control situation, the clutch is locked slightly more than normal, the four wheel drive is always guaranteed when required.
For maximum xDrive performance, tires (and wheels) of the same diameter should be installed on the vehicle."