after having owned a bunch of sport bikes, every single one I had the OEM speedo's were WAY off, they always had cheat built into them, some up to 15+ mph once you get over a 100.
one of my tamer bikes a SV1000s, would read 88 when you were only going 75, it made you always have to speed to ride on the hi way, was never a problem
could just about squeeze 100 out of first gear, but stock gearing would max you out at about 140-145 on a radar
My ZX9R was about the most accurate, just maybe 5-6 mph off! LOL
and all my GSX'r (750' s- 1,000's) were about 12 mph off once over a 100 mph!
don;'t recall what the rest were off the top of my head, but I never owned a street bike that was true to the speed you were going! I think they all add cheat to make them faster to the riders and who know's maybe even for safety reasons,
to show faster yet be going slower, maybe some guys would back off??
I was always too dumb to do that! LOL had to always find out the top end, far too many close calls too!
but something about having a machine that can go"X" and not trying to get there??
that just never sat with me, always had to try and see what it would really do!