Luxury Coach Lifestyles - View Single Post - Tire size-speedometer calibration

The Newell · 01-26-2008, 08:24 PM

Yes, it could. Assuming 9" rims, roughly, the 80 tires would have a 7.2" depth while the 70s would be 6.3".

Adding each to the rim radius (11.25") results in 18.45" for the 80s and 17.55" for the 70s. The difference is 0.9", about 4.9%, which would result in a speedometer reading about 3.2 mph high. Not all the difference, but obviously significant.

01-26-2008, 08:24 PM	#2
The Newell Senior Member Join Date: Dec 2005 Location: Southern California Posts: 1,018	Yes, it could. Assuming 9" rims, roughly, the 80 tires would have a 7.2" depth while the 70s would be 6.3". Adding each to the rim radius (11.25") results in 18.45" for the 80s and 17.55" for the 70s. The difference is 0.9", about 4.9%, which would result in a speedometer reading about 3.2 mph high. Not all the difference, but obviously significant. __________________ 1976 Newell Classic (Sold) Home Base: Riverside, CA If anyone needs my contact info private message me and I will send it to you. -Joseph-