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.
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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-
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