I'll preface this by saying a speedohealer is the next bike purchase...that being said, is the speedo error constant over the range of speeds? For example I know that when my speedo reads 35 my actual speed is 30 (via radar). I calculate that to be about 14% error. Will that 14% stay constant at higher speeds, for example at about 60 mph my speedo should read 70? I have heard that factory error might be as high as 10% but I also have an aftermarket front sprocket messing up the equation. Anyone?
The factory default error and your gearing change are what is throwing it off. I just installed a SpeedoHealer myself since I added +2 on the rear sprocket. The documentation for the Gen 6 said that there is a 7.7% factory error that was calculated using GPS. Using the SpeedoHealer calculator, I used a 5.5% factory error (just to go low) and punched in my gearing change and it indicated that I would have a 10.4% error combined. It is this that I programmed the unit for. To answer your question, I don't know if the error is constant, but I believe that 5.5% (which is the SpeedoHealer default) and 7.7% is in the ball park for stock gearing.
Thanks for the reply, after I posted this question I ended up buying a speedohealer on ebay so it should be in the mail.
To answer the question: the % speedo error does not remain the same with different speeds. The shape of the tire and hence circumference of the tire changes with speed. The amount of this change varies depending on the tire characteristics as well. Also at speed the amount of weight on each tire changes again changing the tire circumference. However, most of these differences are relatively small and with the right correction factor you should be able to get within 1-2%. The main error in most speedo's is deliberate on the part of the bike manufacturer to make it seem like the bike is going faster than it really is.
