wheel size Vs mpg

[ATL_driver]

on my land rover disco, when I fitted big mud tyres it made my speedo spot on, was so far out before, also come to think of it was my focus when I went from 15's to 17's was 7mph out, said 77 at 70 all standard, then was bang on GPS once modded


good old cars hey

[Noel Brig]

even tyres of the exact same dimensions can give very differant readings. All the tyres in the following picture are 175 65 R14 (middle one has 5.5mm tread out have 8.5mm tread) and as you can see the outer ones have a much bigger diameter.)
The middle tyre (summer) make my mileometer read high by 1.7% (shows 101.7 for a true 100 mile) and the outer ones (winter) make my milometer read low by 0.9% (shows 99.1 for a true 100 mile)

All makes quite a difference if you are trying to establish true mpg.

[Image: vii1qs.jpg]