Run Flat limits

[ard]

Originally Posted by Pat68

Hi ard,

Thanks for the warning

Do you mean rolling circumference?

The static diameter of the new rear tyres is <1 cm greater than the fronts, which considering the fronts are part worn I think is quite close. That said, this gives a difference of 18mm (3/4") in the static circumference front to rear.

Do you know if there is an allowable difference/tolerance and if so what it Is?

Thanks Pat

Technically it is 'rolling diameter' or 'rolling radius' (since the tire deflects when rolling it really isnt a perfect circle so there isnt a circumference per se, or the circumference just gets distorted and doesnt change.)

0.75 is WAY TOO MUCH.

The stock BMW tires allows up to a 1% variance. We actually dont know the actual specification, but certain BMW wheels from the factory come with (I think) 712 rev/mile on one axle and 720 on another 8/720=1%. Hence one might infer that if BMW ships cars with that mismatch, that the engineering allows at least 1% tolerance

Stock size is roughly 29.0"... 29.0 versus 29.75 is way more than 1% You are probably running 3 times the tolerance.

You are likely stressing, perhaps wearing and maybe overheating the diff.