I'm hoping the mileage markers on the highway are fairly accurately spaced, because that's what I've always used, checking speedometers on cars or my bike.

I lock it at 60mph, and time a mile with a stopwatch ( YEAH, it's a lot harder on a bike!!! LOL ) If all is on the money, you obviously should be going a mile per minute. Using this method, my 929 speedo seems to be dead on with 16 front and I bumped the rear down one to 42.

And in case anyone's wondering, yes I feel really stupid talking about this.....[8D]