Mix&match tyres

[auspom]

Hi folk, just bought a rather nice 80 tdi avant(pics to follow!) and need to change the front tyres. The steels that are on it are wearing 195/65x15 tyres all round. I have lying around a good pair of 185/55x15,s but not sure wether this will upset the ABS, I,ve heard stories that if the rolling radius is different front to rear it upsets the ABS signal and causes the warning light to come on and seeing as the Mot is due in six weeks I need to make sure this doesn,t happen. Any advice is welcome.

[4v6]

Shouldnt have any effect on the abs function.

The abs works by a sensor on each wheel detecting a signal ( alternating voltage) that corresponds with wheel rotation.
The abs ecu monitors the voltage coming from each wheel looking for a no voltage condition.
if that happens and it corresponds with pressure in the lines and possibly input from a G sensor then it modulates the pressure to that wheel cylinder to unlock it.
The locked wheel corresponds to a no voltage output from the wheel sensor.

If you think about it, the outer wheel always turns faster in a croner than the inner yet no abs warning gets shown, the same thing applies here too.
I think.

[auspom]

Thanks for that 4v6, I,ll give it a go then, just a 'get me out of jail' thing for the up and coming Mot.