Speedo inaccuracy?

[bobmaclaren]

Just finished building a 165bhp VVC Roadsport with all the toys, and passed its SVA yesterday so looking forward to having some fun!

I've gone for the R500 13" wheels, but was wondering if anyone had any idea of how much this must throw the speedo accuracy out, knowing that they're not exactly accurate to start with....?

[jack&mle]

My 21 with the 16" rim and 205 45 is about 16% out, an indicated 100mph will be about 88mph.
I've calculated it with help of rev counter

Jack