That’s probably why we rarely see the actual test parameters and data.
I understand Specialized motors very well, especially as Specialized gives the peak power for each motor together with the marketing torque value. It is clear that Specialized uses 60 rpm as the reference (Yamaha does the same). Therefore, the listed torque values for SL motors are fair enough. When it comes to full power motors, Specialized marketing says 50, 70 and 90 Nm. However, these figures are 68, 75 and 90 Nm.
Fancy you are choosing between three differently priced e-bike models. You look at the 50, 70, and 90 Nm specifications. Which e-bike would you choose? Not the most expensive?
While it turns out the weakest motor declared as 50 Nm is actually almost 70 Nm strong!
Like choosing a cadence for mid drive could one choose a average speed for doing the calculation (say 10kmh)?
There are several aspects of using a mid-drive as an excellent climber:
- If a low gearing can be used, the rider can pedal at a very high cadence even at a very low e-bike speed. That makes the mid-drive motor very efficient. Most of electrical power will be converted into the mechanical power at low losses to the heat
- For gearing ratio < 1:1 (alpine or MTB), the torque at the rear wheel will be amplified. That's why e-MTBs often have a (say) 34T chainring but a 51T "granny" cassette sprocket. The gearing here would be 34/51 = 0.667, the reciprocal being 1.5x, meaning 1.5 times amplification of the rider + motor torque on the rear wheel
- If the rider can spin the crank on climbing, often a high leg power can be delivered.
Examples:
-- The Bosch SX is a lightweight motor of derated peak power, designed for use with gravel and road e-bikes. In case the rider can pedal at the cadence of >100 rpm and a special assistance mode (SPRINT) is used, the motor will unleash its full 600 W of peak power if the rider also provides enough own leg power
-- Recently, I was riding along my friend riding a Bosch Performance e-bike. Her motor peak power was twice of what I had on my Specialized SL 1.1 motor. If we pedalled similarly, she was obviously faster than I on climbs. However, I once dramatically downshifted and mustered a cadence of 129 (it is a
very high cadence). My max leg power reached 417 W, and the motor was saturated at 240 W. I just "smoked" my friend on that climb! It was as if I were lifted by an elevator up that hill!
The issue with the hub-drive motor is it hates spinning slowly. There is no relationship between your drivetrain and the motor. As your speed drops, the hub motor efficiency and torque drop as much as you can only recover by putting a very high leg power of yours (that was what
@mschwett was talking about earlier).
