Tyre sizes

[Guest]

I may be being a bit thick but how does this make the speedo more accurate?. I would have thought the speedo would be more accurate with standard tyres on and less accurate with bigger ones

With standard tyres on my speedo ran about 10% over. Think they may well set up the speedo for the optional 31" tyres that were a factory option.

With 31s on the speedo reads about 5% over.

Cheers