Thread: Adjusting the speedometer for larger tyres?

Originally Posted by e3j

Well, I dunno......I have the opposite problem to the rest of you.....when my '02 Disco 2 td5 auto reads 100 on the speedo, the gps reads 103! This is on standard tyres. Mind you I'd better not complain, 'cos that makes it technically illegal!

Seriously though, can anyone explain why this would happen?

Maybe because the tyre diameter is slightly less than standard, even if the dimensions quoted are standard size. There is some variation between brands. Or your tyres are very worn.

Originally Posted by biggin

Maybe because the tyre diameter is slightly less than standard, even if the dimensions quoted are standard size. There is some variation between brands. Or your tyres are very worn.

No, the other way around - the tyres are slightly larger. I have the same thing on mine when I put new Michelins on. Tyre size says stock but the speedo is out.