Trying to sort out the crabbing issue on my GLC43. Bought it with 21" alloys and the dogsh*t continental tyres.
Front 255/40 R21
Rear 285/35 R21

UK - based and can't find matching front and rear All Season tyres in R21, so moving down to R20 alloys.
Currently sat in the Mercedes dealership and the parts department can't tell me what tyres to order for R20 alloys. Presumably the tyre profile needs to increase to maintain circumference of the overall wheel and therefore not effect speedo?

Has anyone had to do this? Pulling my hair out trying to get anything helpful from the dealership. The guy from the Parts department here literally told me I'd have to ask Mercedes. I guess I'm the idiot for thinking that's what I was doing at the dealership talking to the parts department...

 

Tiresize.com has a calculator for comparing wheel/tire combinations. You can plug in various profiles and see how they compare with your 21" setup.

 

Thanks, that is a useful site! Used the speedo calculator and looks like making that move from 21 to 20 with a minor tweak to profile only puts the speedo 0.5mph out at 80mph, which I can live with.

 

Front: P255/45R20, rear: P285/40R20