Tyre profiles and speedo.

[waldershelf]

When I changed from the standard 205/80/16 on my Land Rover to 235/85/16 the speedo went from over reading by about 10% to reading bang on, according to my sat nav.

 

[TAITSIE]

This is a good site for tyre size comparisons, also gives you speedo graphs

http://www.ajdesigner.com/fl_tire/tire.php