Depending on the bike, they are +/- 1 mph according to the GPS.

 

A lot depends on what tire diameter it was calibrated for. Even tires of the same size can differ in their outer diameter by quite a bit. With the stock Dunlops on my RK, my speedo was showing two mph faster than I was actually going. 60 was actually 58. With my Michelin Commander II tires, that difference is 4 mph. 60 is actually 56 mph.

If it's an electronic speedometer, the dealerships "should" be able to calibrate it based on the overall diameter of the tires you're running. But I don't know for sure that they can do this. But they should be able to.

This is the reason most cops won't bother pulling you over when you're around 5 mph over the speed limit. Calibration of speedometers has always been an issue, even though on modern vehicles it shouldn't be.

 

speedo app on my phone says 3 miles per hour slower that reading at70. most honda;s I ride with are dead on

 

My deluxe is 5 mph higher than what those led signs read. My brother and dad have the same thing with their bikes. My dads is worse though...about 8 mph off.