I have been researching tire options and notice that the Overall Diameter quoted doesn't seem to calculate to the RPM numbers. I didn't check them all obviously but for example the 245/40 ZR17 RE050 shows RPM of 847. Yet I calculate 820RPM using the 24.6in OD.

Are your numbers test numbers or is some factor applied to the calculation? I got into this trying to figure out what the odometer errors might be with different tire options.

Thanks

 

Effective LOADED radius is less than half the diameter, that's why the revs/mile are greater than you'd calculate from the OD measurement.

 

I looked back at some of the specs I have and I notice Static Load Radius in the RE050 specs and it is less than 1/2 the diameter. I bet their computer designs give them that number. Thanks for the tip.