Quote:
Originally Posted by Dadhawk
Yea that would have been interesting. Odometers are relatively accurate but not 100%. Used to be that they rolled backwards in reverse which is why you could take a hand drill or other tool and literally turn back time (well miles) on a car (pre-70ish I think is when that stopped).
Current ones are more accurate but could be impacted by a change in tire size, just like a speedometer. They are also impacted by tire wear. As the tire wears, it becomes smaller making the odometer reading higher.
If the odometer is based on a 24.6" tire (that is new calculated circumference of a P215/45R17 tire) for every 1/8" of tire tread wear you gain 25 feet of measured ground per odometer mile. That means for every 211 miles you travel your odometer would be +1 mile off.
Now, I'm not sure if odometers are calculated for medium tire wear so that it balances out over time or not, of if some odometers use a different measurementh other than tire rotation and size.
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My observation over the last 100k or so is that the speedo is spot on when my tires are new and gradually goes to about 2 over as they wear. My mpg also goes down as the tires wear. I figure the correlation is, because they're registering slightly higher miles traveled it manifests itself in speed and mpg being off by that percentage. I wouldn't mind finding the right tire size so that it's both over and under so it's more accurate.