Spedo way off

[Poseidon]

Hi all i have a 1996 2.3 auto ranger and my speedometer is about 17 mph off. It has 235 75 15s i know it could have came with 14s. But i dont think it would be off by 17 mph just because of the tire size or am i wrong?

 

[adsm08]

Is it a consistent flat 17 MPH across the whole speed spectrum, or is it 17 MPH off at say 55 or 60 MPH?

Speedometer errors caused by tire size or gear ratio changes are percentage errors, so the faster you go the greater the error in terms of MPH.

 

[Poseidon]

as far as ive seen its never less than 15 off and i haven't seen it more than 17 off