The Suzuki Burgman 400 and 650 maxi scooters are widely agreed to be 10% in error, so when riding at an indicated 60mph the actual road speed is only 54mph. Of course this also means that the odometer over reads so any mileage computations will also be incorrect.
Japanese motorcycles generally read around 5% - 10% faster than you are actually going. I believe that the odometers are much more accurate. For my bike, a Yamaha FZ6, I am reading close to 10% high on the speed but very close (maybe 1%) on the mileage compared to my car.
> Of course this also means that the odometer over reads ...
Not necessarily, that would only be true if the +10% on the speedo was the result of a misadjustment. It is usually done deliberately for legal reasons (which is why the odo is often accurate when the speedo reads high).
Yup - my (I mean Teresa's) speedo reads high, while the odo reads a bit low. I checked it both with road signs on long, undisrupted motorways and google maps, and I'm pretty sure she's a bit too modest about the distance. I think it's something legal again, not to shorten the maintenance period, imposing extra cost on the customers. Or something similar.
Also, it changed a bit when I replaced the old Metzeler Z6s. Now with these Heidenau K73s the odo is even more off. This is why I correct the distance by 1 percent. I'll replace these tires this winter, we'll see how the new ones perform in this respect.