I have seen different threads on multiple forums ranging from 10 - 20% difference from crank to wheels... (all minis posts) Is this one of those things that varies from mini to mini? Or is there a more accurate range for the loss?

 

It will vary slightly from car to car but 15-22% is the average loss for a 2wd manual transmission drivetrain. By the time alternator, trans, axles, and wheels are all accounted for, it ends up in that ballpark. Automatic it's a little more and AWD really adds power loss.

 

It is only here in the Mini that many uses 12%.