speedo

[skov]

Not sure about bikes, but cars often use a '1 pulse per mph' signal for the speedo.
If your bike speedo expects the same, then it might just work!

If it's only a little way out, then making custom faces for your speedo could be an option. There's some great instructions on making some here:
http://www.revlimiter.net/mods/gauges.php

Failing that, I guess you'd need some kind of electronic trickery to convert from the car pulse to the bike one. Someone must make a box to do that somewhere!