That would be a sound number if you assume drop bars, high pressure road bike tires, and an aggressive sporting rider position. I have seen no bike here that conforms to this plan. What I see here mostly is chunky (or even knobby) tires that people have slowed further with puncture preventives, mounted on bikes with upright riding positions.
I use the
power calculator at kreuzotter.de. When I calculate power requirements for a motorized bike or e-bike, I set the parameters for "roadster" because that corresponds most closely to the MBs and e-bikes I have seen.
As speeds rise above about 20mph, aerodynamic qualities become the driving factor, and rider position makes an increasingly large difference in top speed.
Chalo
I based the calculations for the power calculator I wrote on the underlying calcs
here. At speed, the bulk of the drag is caused by aerodynamic effects, with drag proportional to the square (and the cube) of the velocity. Rolling friction is by far the smaller proportion of potential losses. Now, the 'chunky' tires you mention add about 26 more square inches to the frontal area than narrow, road bike tires, and
possibly a small amount of additional rolling friction. (that 26 square inches is about 2.5% of the area of an 'upright' rider, and about 3.5% of the area of a 'typical' road biker. In any event, an approximation of cross sectional area is calculated, based upon rider weight. Oddly enough, tubular tires on a time trial bike actually had about 10 percent
higher measured rolling resistance than street tires on a commuter bike.
Any engineering tool contains assumptions; I've removed (or reduced the effect of fixed assumptions) by allowing the users to enter air temperature (which affects air density, and therefore drag) as well as an adjustment for rider position (upright, forward, and reclining) and the resulting effect on cross sectional area and resulting aerodynamic drag.
Also remember that any of these tools provide estimates of maximum possible performance; many, if not most of the bikes here are compromises, with trade-offs between top speed and acceleration. (This means that the motors are often
capable of driving the bike faster than they are geared to run. This is certainly the case of my bike; it accelerates right up to the RPM limit of the motor.) The CVT helps to overcome these tradeoffs; by sacrificing some top end speed, they allow better acceleration than a fixed gear system possibly could.