15% error
 

Ran the measured mile the other day(2mi.)and my odometer read 2.3 mi. It seems as though the miles I,ve been putting on have been reading higher than should be.I,m running a new set of SO2's 245x45x16 and 225x55x16 on factory Fuchs 7 and 8's. On the freeway it also appears I,m doing 80 going along w/ traffic when I know everyone is not at 80.
88 Carrera w/ less than 40,000 mi.
Any and all resolutions welcome


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Wild Willie 88-911

stock sizes on your car are 205/55 and 225/50. I think some of the error is in your back tires. The 245/45 is enough off in the sizes that it is throwing your readings off. Most people like myself want to put as much rubber on the road. Without going to wider and larger rims and matching the original tire diameter, its going to be hard to avoid odometer error. Most tire stores can give you the actual amount a certain size and ratio aspect will be off.

According to my calculator, there is less than 4 mm difference in height between the 225/50-16 and 245/45-16 tires, so that would be less than 1% error attributable to the shorter tire! My suspicion is that the electronic speedometer is at fault, and I have no info on any internal adjustments that can be made, but one would think there MUST be one. Bruce Anderson lists three contacts for VDO instruments ... a call or letter might give you a direction to go, next.

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Warren Hall
1973 911S Targa