How out are the standard clocks?
 

Seem to remember someone saying 7% or something

IE a displayed 140mph on the cossie speedo is actually 130mph

Has anyone match this to there GPS?

I'll have a look when i got my sat nav in the car on saturday.

If i remeber right tho its just that same as most cars ie only slighty out.

I will post my findings

As a rule it is around 8%, i.e. a reading of 70 on speedo is 64.4mph
I was showing with standard wheels, 161mph on the speedo and 151mph on GPS, then on 19's it read 160 on the speedo and 160 on GPS :top:

yep got about the same difference in speed on mine. :top: