Motor speed for 16" wheels

[Tangsoo]

if a motor rated a 260 or 255 rpm@ 36v was installed in a 16" wheel my calc's say 12.7mph. Spinning the motor up on 48v gives (33% increase) @ 339RPM and 16.9 MPH?

As my ride in to work is pretty constant, very few junctions, some 3 mile straights but one steady climb over 1.4 miles, is it practical/advisable to run a motor at max RPM for longish periods or is it best to go for a faster wound motor at the expense of torque?

 

[Deleted member 4366]

Power drops off rapidly once a motor spins faster than 75% of it's maximum RPM.For maximum efficiency, you want it to run also at about 75% of its maximum RPM when at your normal cruising speed. for maximum power, you want it to spin at about 2/3 of its maximum rpm.

The basic calculation for bike speed for a motor is:

Bike speed = 15mph x (motor rpm)/201 x (wheel size)/26 x (nominal battery voltage)/(motor designated voltage) x 1.1

 

[Geebee]

Or if you are lazy like me. stolen from http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=16114

 

[Deleted member 4366]

That table gives the actual RPM of the wheel at those speeds, which doesn't correspond with the designated motor RPM because the voltage is normally higher than nominal.

 

[patpatbut]

I have a SWXB clone motor running 340RPM at 36v. The loaded speed is about 17mph (39v nominal) on my brompton.

hope it helps
Pat

 

[Tangsoo]

Thanks for the replies. I have a mac 255 rpm motor (@36v), think it'll be run at 48v. I guess the rub is, is it worth getting laced into a 16" rim? I'd be happy with 15mph, as long as it pulls well on the hills. Undecided about putting it in a F/S mountain bike...