On 13/02/2019 21:39, alan_m wrote:
On 13/02/2019 18:12, Robin wrote:

depends on wheel/tyre of course but I was reckoning on tread going
from 8mm to 2mm on a tyre of around 180mm circumference.


What about different minor variants of the same basic car?Â* It wouldn't
be unusual for them to be fitted with either,say, 16 or 17 inch wheels.
Do the manufactures adjust the calibration for different factory fitted
wheels or do they rely of range they allowed on the speedo readings?

What about the reading within spec with a space-saver wheel on one corner



You aren't supposed to drive with the space saver on the front so that
removes front wheel drive cars from the equation.

They nearly always recommend swapping the wheels so the space saver is
on the rear.

People don't of course because they are too idle.