Quote:
Originally Posted by bschloop
Here is a simulation for a brushless hub motor in a motorcycle. It should give a better representation of efficiency as it relates to speed.
The black line represents efficiency. Notice the bump and subsequent drop as the vehicle approaches top speed. This coincides with the steady state curve I showed earlier. It seems that efficiency is greatest just before top speed in this simulation. It also shows that efficiency is about 20% lower at half of the top speed, and over 40% lower at a quarter speed. All of this supports the need for a multi speed transmission. It also makes me think more that Brammo might not have made a mistake in their design. Maybe the reviewers simply didn't understand the proper use of the transmission as it relates to extending range aka increasing efficiency.
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You are interpreting the graph slightly wrong. This is from ebikes.ca, right? You are not at 60% efficiency at half of top speed. You need to adjust the throttle setting to 50%, then you will see an efficiency of about 3-5% lower than peak, likely.
It is true that you are at lower efficiency when the motor is spinning slower, especially at the very low speed end, but the difference is not as great as you say.
It all has to with load and throttle position. If you spend enough time riding an EV and watching the watt meter, you will see that the throttle technique can change your efficiency a fair bit, depending on load and terrain and change in speed. Riding WOT, especially on an EV with good power output, with indeed kill your efficiency.