Quote:
Originally Posted by ard
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.
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Hi ard,
Once again thanks for the info.
I think I may have confused the issue a bit, I quoted the circumference of the tires, not the diameter......
I work best in metric so will try to give best info possible, even though they are metric size tires on imperial rims ???!!!!
Fronts, 50.8cm (20") rim, 11cm tire height (×2) = 72.8cm diameter (new) - 0.8cm (wear) = 72cm.
Rears, 50.8cm (20") rim, 11.025 tire height (×2) = 72.85cm diameter
Total difference 0.85cm. Which I think works out around 1.1% so only just outside the BMW 1% spec.
If my maths or understanding of your info is incorrect, please correct me. It's been a long time since I left school and college
Pat