ABS Coding when upgrading to R32 Fronts

[RedRobin]

Well the circumference of the wheel and tyre for 17" and 18" is the same (or should be) so no change. 

Simples!

....Gotcha! Thanks  - I wrongly assumed you meant the wheel diameter without tyre. And of course the overall diameter/circumference measurement transferred to the road is what matters. Ta for explaining 

[Eddie-NL]

Had this old chestnut on the Mk4s it's actually coded to wheel size not brake size.

....So am I right in understanding that if your car (Mk5 GTI) left the factory with Monza 17's and you later changed them to 18's, and you didn't do any VCDS coding revisions, then your ABS would be working 'inaccurately'?

You should code
http://wiki.ross-tech.com/wiki/index.php/VW_Golf_(1K)_Brake_Electronics_(MK60)#Coding