This would be quite pecculiar because in all vehicles the speedometers are purposely overoptimistic. This is so that one can never claim that broke a road limit misled by his/hers speedometer.
In all hondas I had, the speedometer offset was about 7%, and I founf the ATAS to be no exeption to the rule. When the speedo shows 100kilometers per hr my GPS indicates 93. At a speed of 215K/Hr my GPS registered a top speed of 199,7.
The odometer on the other hand, is dead accurate; but of course deviation may be expected as the tires wears out.
And my US model reads between 2 and 3 mph high at 70, according to GPS--3.6%. I thought it read way high at first, but it was just because it was smoother than all the other bikes I've had, and I was speeding...