It is more money - but I will be investigating this from VaporTech. Not only can you adjust the mph to correct for changing over to sprockets and chain - it also can do the following:
Speedometer:
Current Speed
Maximum Speed
Selectable MPH/KMH Display
Tachometer:
Real-Time RPM Bar Graph
Numeric RPM Readout
Dual Programmable Shift Lights
Up to 20,000 RPM
Temperature:
Ambient Temperature
Engine Temperature
Dual Programmable Temp Lights
Exact Model Fit Temperature Sensors
Selectable °F/°C Display
Distance:
Adjustable Distance
Permanent Odometer
Selectable Mile/Kilometer Display
Clock:
Hour Meter
Stop Watch
Ride Time
Accumulated Ride Time
permanent Hour Meter
Selectable 12/24 Hour Display
Here is the link to their website:
http://trailtech.net/vapor.html