"Thanks", MetroMPG for the writeup on Odometer readings & Google Earth's uses. Reading it reminded me of something I haven't thought of for a while. I'm sure this is like splitting hairs, but where else could I take this question--where I wouldn't get laughed at? Here goes:
Has anyone ever wondered, or better yet FIGURED what the odometer difference would be between a given set/size of NEW tires versus balding tires? Since the circumference of a new tire is certainly larger than a bald tire, there is obviously a difference to be calculated; I just wonder what it is. Once again, calling all geeks on this one. I'd love to know the scale of difference, but I've not done the experiment myself (yet).
Most tires have 9/32 to 11/32 of tread depth where the last 2/32nds are considered illegal. So a tire at the legal limit would be about 1/2" less diameter. So for the example given previously you would have 909 revs/mile. That would lead to a 2.4% odometer over-registration. That is assuming that your odometer was dead on to begin with.