| The 998 and 748 hub speedometer gears are the same. The speedometer error for a 998 with a 70-section was measured against a GPS standard by one owner to be:
40 998 = 37 GPS
50 998 = 46 GPS
60 998 = 56 GPS
70 998 = 65 GPS
80 998 = 73 GPS
90 998 = 82 GPS
100 998 = 89 GPS
If you switch to a 60-section tire (that comes standard on a 748,) the circumference is smaller than a 70, so the wheel sees more revolutions per mile and the speedometer reads higher. Consequently, the speedometer reads closer to the true speed (still low,) and it’s more accurate on a bike with a 60-section tire. | 
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