I recently picked up a 1988 CBR600F and have been working on fixing it up and commuting on it. One thing that is driving me crazy is how optimistic the speedometer is. To do a true 60 mph (GPS) I have to ride at an indicated 70. To run the freeway speed limit of 75 I need to be showing 88 mph.

Anyway, are there different speedometer gears available to get things a little closer? One of my other bikes (DR650) has this option thru aftermarket for guys that have gone supermoto (big tire height change). I have searched but come up empty for this 32 year old toy.

Thanks for any help.

 

That much deviation seems strange. My bike with stock tire size shows almost exact kph values. What size front tire yours has? How about odometer, is it close to true miles?
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An old 110/70/17 Metzler is on it now, which doesn't help things. I need to check odometer/trip still.

Seems to be about 16% off all the way through, from 30 mph right up to lose-your-license speeds. In other words, doesn't seem like the needle rotated on the pin or anything (which would be offset by a straight speed, not a multiplier).

 

That tire size increases speedo and odometer readings just 3%. If your odometer accuracy is close to that figure, I think there is a mechanical fault in your speedo.