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Archive for November 2nd, 2006
Tire Size Change Affecting Odometer & Speedometer?
Posted by Sam on November 2, 2006
I have 225/45R18’s on my vehicle now. I am looking to downgrade to 17 inch wheels and getting 225/50R17 for the winter. Will this disrupt my odometer and speedometer readings? I have looked at each tire. The tires I have now have 804 rev/mile and the tire I am looking to get for the winter has 798 rev/mile. If this does affect the readings, how much does it affect them?
If anyone out there wants to comment on my answer here, I will more than welcome it. I assume that all vehicle odometers and speedometers calculate distance and speed by counting tire revolutions. By changing the diameter (and the revolutions per mile) of the tire on the vehicle, you can't help but affect the accuracy of this reading. In this case, since the revs/mile are less for the new tire, the odometer will think the vehicle has gone farther than it really has gone and the speedometer will say it is going faster than it really is. In this case, the difference in the revs / mile between the two tire sizes is less than 1%, so at normal highway speeds, the speedometer will be less than 1 mph off and the odometer will be off less than 1 mile for every 100 miles traveled.