Legal CYA, as far as I know. The manufacturer's never want to be in a position where they are instigating speeding, all the more so with sport bikes - I'm sure the speeding ticket to mile ratio is much higher for your average sport bike than a Toyota Avalon. By consistently calibrating their speedometers to read low, they eliminate any and all liability when it comes to speeding tickets.
Mine's off by quite a bit and I had looked into this as well. Supposedly there's a method for adjusting your cable speedo. I found some instructions on it.. as soon as I can pull them out I'll post it up, you can make your own call.
1-7 (deals with removing the instrument cluster)
8. Install a square drive bit into a drill. (Most drill accessory kits have them. There are 2 or 3 different sizes. Find the size that will fit into the speedometer cable coupling on the back of the speedometer.) I used a cordless Dewalt drill. Make sure that you use a battery with a good charge. What you want is a constant speed reference. A corded drill might even work better. Might turn faster giving better resolution. My Dewalt would only register about 35 mph.
9. Hold the speedometer on the drill and turn the drill on full speed and read the mph indicated. Mine indicated 35 mph.
10. If your speedometer reads faster than it should, like mine, take the indicated 35 mph and divide by the percentage that it was off (7%) to get the new calibrated speed of 32.5 mph. 35/1.07=32.5 If your speed was slower you would multiply instead of dividing.
11. Now look at the back of the speedometer. There is a small spring coiled around the speedometer shaft. This coil is held by a small bracket
that is crimped to hold the spring. If you need to lower your calibrated speed as I did you need to bend the bracket in the direction to tighten the spring (Moving it closer to the odometer wheels). It doesn't take much. I used a pair of needle nosed pliers. Make sure you do not leverage off of the round bell that is attached to the speedometer shaft. You do not want to put any pressure on the shaft. Make sure that you do not hold onto the speedometer face or touch the needle.
12. After the adjustment, put the speedometer on the drill again and check the speed. Keep adjusting as necessary.
13. When the speedometer reads the correct calibrated speed make sure that the small piece of spring that extends past the crimp on the small bracket is not touching the odometer wheels. Bend over if necessary.
14. Reassemble the speedometer in the reverse order. Install on bike.
In my early sports car days I did some Time Speed Distance Rallies. In order to turn at the right place when an instructions says "Go 4.4 miles and turn right". Your speedo had to exactly match the one in the car that set up the instructions. Other instructions would say go 3,2 miles at 32,4 miles per hour.
What they did was set up a 10 mile check. When you reached the 10 mile point you matched your Odometer reading to 10 miles and got a correction factor 10/9.7=1.03 or 10 /10.4= .961 this was you correction factor, and it needed to be factored into every calculation. This was 1960 and no calculators.
You can plainly see why our generation is smarter.
The point is you don't need an electronic gadget. just do a 10 mile check and you'll know your error.
they use one of these at the chinese resturant down the street from me. the lady is so good with it, ive actually seen her calculate things without even having one in her hand... she just pretends she has it.
As far as I know most people have said that this bike is off by 10%, which is what I have figured mine to be. There that took 2 seconds and my bioelectric processor calculates automatically when I look at my speedo, instantaneously too I might add.
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