Q: Why is my speedometer reading off?
A: All bikes have a speedo error, even from the factory. Speedo errors from the factory can be off by as much as 20% (so I've heard). I've been told by several shops that if your factory error is greater than 10%, you should have the dealer fix that. Speedo errors are also created/exaggerated by changing tires sizes, wheel sizes, and gear ratios.
Q: How do I correct the speedo error?
A: There are several speedo recalibrators out there. But these recalibrators will only work with electronic speedo sensors (so you F2 and older bike owners cannot use them).
The Yellow Box is probably the most popular one on the market. PVD also constructed a home-made wiring harness so that the Yellow Box installation is plug-n-play.
Another speedo recalibrator is Jim Ahlman's speedo recalibrator. This one is nice because installation is plug-n-play, i.e. no splicing required! Plus, its cheaper than the Yellow Box.
Other members have used the SpeedoHealer. This is also a plug-n-play unit.
Q: How do I determine my speedo error?
A: You'll need to compare your actual speed with your indicated speed:
(indicated speed - actual speed) / actual speed * 100 = speedo error %
The trick is to get your acutal speed. Some methods used by our members have been to mount a GPS receiver, get tagged by a radar gun, get paced by a vehicle with a calibrated speedo. I'm sure there are other methods as well.
Q: Changing sprockets will also affect my speedo but by how much?
A: The math is actually quite simple:
Let ratio = (# teeth of front sprocket) / (# teeth of rear sprocket)
speedo error % = ( (old ratio - new ratio) / new ratio * 100) + stock speedo error%
 badfish'05 600RR Purple/Black |  |