I just installed a Schwinn bike computer on my 650 (<$10 Walmart). I measured 1699mm for the front wheel though. That's with new original tires.
Just playing with the math...
My 1699 is 98.5 percent of your 1725.
Your GPS 92 is 98.9 percent of your sigma 93.
Your susuki 100 is 99.6 percent of your sigma 100.41
I don't know if you're using the same tires as I, but it seems like changing your wheel circumference number a little lower might get your sigma closer to all these other sources. 98.9 percent of 1725 would be 1706. Your k/h would then be as accurate as your GPS, and the ODO reading would would only be slightly lower than the Suzuki's, which I suspect to be a bit off anyway.
Just a thought. I'm gonna put some trip meter miles on the bike and my Schwinn and see how close they are. I'll let you know what I find.
That's a shame, Ray. In Kansas the police give everyone about 10 MpH tolerance except in school or road-work zones. But we have enough people that even drive faster to keep them plenty busy. I'm used to KNOWING I can go 35mph in a 30, 79 in a 70, and never get a ticket. With the Burgmans's speedo error I was getting a headache trying judge my speed.
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