speedo drive gearing?

[mavis cruet]

im thinking of changing the bevel box on my bike and wondered if/how you change the speedo gearing to keep the reading accurate? as a side thought, what happens if you change your wheel size? do i have to get a speedo to match or is there something you can do with the drive coming out of the gearbox? any thoughts appreciated... karl.

 

[fayeslane]

The easiest, cheapest and most accurate way to guage your speed is with a GPS. Might be easier than making mechanical changes. Standard speedo will be up to 10km/h out. GPS is not influenced by wheel sizes or changes in tyre profile. Not answering your specific question but presenting another option

 

[Kenny]

The easiest, cheapest and most accurate way to guage your speed is with a GPS. Might be easier than making mechanical changes. Standard speedo will be up to 10km/h out. GPS is not influenced by wheel sizes or changes in tyre profile. Not answering your specific question but presenting another option

This is the route I'd take as well

 

[mavis cruet]

gps's arn't particularly cheap though. i'm after a more permanent solution really