You guys are turning an easy problem into a difficult one. Take your scoot out and run it in 5th gear at 5000 rpm. Mine goes 67mph at 5000 rpm. (Notice that these speeds are legal) Then if you use a redline of 9000rpm your top speed is 67 x 9000/5000 or 120.6 mph. If you go to 10,000 rpm then the top speed is 67 x 2 or 134mph. Unless your clutch is slipping or your belt doesn't have any teeth, these numbers are fixed. This works because the entire driveline is locked. Then number of rear wheel revolutions is fixed to the number of engine rpms. In our case, the ratio of speed/rpms is 67/5000 or 0.0134. All you need do is multiply your rpms by 0.0134 and you will have the resulting speed. It does not matter whether you are going up hill or down. RPMS TO SPEED IS FIXED.
Your ratio may be different depending on your rear tire diameter and possibly other factors but once determined it will not vary.
To go 145mph you would need to go to 10,820rpm. This is way above redline unless you have tinkered with your engine settings.
Also note that your scoot might not get to 9000rpm due to wind resistance from that large frontal area. But, again, rpm/speed doesn't vary.:lecturef_smilie:
I think Scotty will agree with me:bowdown: