Motor RPM vs. Crank RPM

[richj8990]

First, please tell me if the two statements below are 100% correct:

"Maximum torque is at zero RPM and peak power is at 65% of maximum rpm, around 45-55 rpm (crank rpm). You go uphill fastest if you keep your cadence to 45-55 rpm, you have maximum assistance but that does not equal to having maximum torque. You have maximum torque when you stall."

"Torque peaks around 1500 rpm on electric motors."

So, if the above is true, does that mean the best reduction ratio for a mid-drive is 30:1? So that 50 rpm crank cadence = 1500 rpm motor speed?

Lastly, not to complicate things, but if there is a separate drive chain from the cassette chain, and the drive chain reduction is set to around 3.0 (the motor's sprocket is say 16T and the motor chainring is 48T) does that mean internally that there must be some internal motor gearing that's around 10:1, otherwise for a direct drive motor with zero internal gearing, in the middle of the bike with a chain reduction of 3.0, the rider would have to pedal at 500 rpm for the best torque efficency?

 

[E-HP]

"Maximum torque is at zero RPM..."

"Torque peaks around 1500 rpm on electric motors."

What's the definition of maximum vs peak?

 

[richj8990]

What's the definition of maximum vs peak?

Interestingly, new gas-powered cars have torque that also peaks around 1500 RPM with a redline of 7000-7500 RPM. It used to be for smaller overhead cam engines that the torque peak was 3000-4000 RPM, but with turbos and computer advancements they were able to lower it to 1500 RPM, which is really nice.

I didn't write the quotes above, I just copied and pasted them. I think the first one means there is a linear inverse relationship between torque and speed (rpm). The second means torque in the sense of efficiency; in the real world the torque curve goes up to a point at 1500 rpm and then declines down as the rpm increases past 1500. So in these two quotes, the term maximum is theoretical and should not really be used for real-world discussions about e-bike torque.

So the real question is: for a two-chained e-bike with one as a motor sprocket to chainring reduction chain, the motor must have some type of gearing inside if the motor reduction chain is only 16/48 or 1 to 3.0, correct? Otherwise it's going to behave more like a direct drive than a mid-drive for torque...?

 

[ebike4healthandfitness]

Torque won't always peak at around 1500 rpm.

That is way too general of a statement.

 

[ebike4healthandfitness]

So the real question is: for a two-chained e-bike with one as a motor sprocket to chainring reduction chain, the motor must have some type of gearing inside if the motor reduction chain is only 16/48 or 1 to 3.0, correct? Otherwise it's going to behave more like a direct drive than a mid-drive for torque...?

On a motor like the cyclone it will also have a planetary gear box providing gear reduction. Otherwise like you say the motor would essentially operate 1:1 when a 3:1 gear reduction via chain is driving a 48T chainring connected a 16T rear sprocket (i.e. a 1:3 gear gear multiplication following a 3:1 gear reduction cancels each other out)

 

[calab]

Some endless-sphere people took off the reduction on their Cyclone 3kw md's, but I cant remember their builds and why they did it. Might have been a jack-shaft with their own reduction to dial in their final speed.

 

[richj8990]

On a motor like the cyclone it will also have a planetary gear box providing gear reduction. Otherwise like you say the motor would essentially operate 1:1 when a 3:1 gear reduction via chain is driving a 48T chainring connected a 16T rear sprocket (i.e. a 1:3 gear gear multiplication following a 3:1 gear reduction cancels each other out)

This is why I think it's a really dumb statement when you read something along the lines in about 100 articles that "Mid-Drives have an advantage because of the gearing, since the gears leverage the torque from the motor".

If the mid-drive chainring is 36T, and the chain is in an 18T cog, that's LESS torque! My experience so far is that most mid-drive motors have so much power that the chain to the rear wheel is simply there to shuttle the power to the wheel mechanically. Gearing down can actually be counterproductive because the motor then can't push the bike past a certain speed due to the gearing being speed limited. Upshifting increases speed uphill, level, downhill, period. Regardless of any 'increased torque' from downshifting. As long as the rear wheel is moving smoothly uphill, pick whatever gear you want, you have the power.