thunderstorm80
1 kW
- Joined
- Mar 29, 2016
- Messages
- 383
dogman dan said:I'll go out on the limb again.
The big difference in winds for hubmotors in 26" wheels, is not the torque. But the increase in efficiency, during that period when the vehicle is going less than 10 mph, with a good load in the form of heavy weight or hill or wind, makes a difference. The question is does that difference matter enough to sacrifice 5-10 mph of top speed? For the vast majority, its not worth the difference.
How big a difference? Not much. But if you have to stop on a mountain, pulling a trailer, with the wind in your face, you'll appreciate the lower rpm version. You might make it to the top with either version, or not, depending on how bad you have overloaded the vehicle. But in years of climbing a big mountain with a CA on the bike, I'm convinced the low rpm motor is more efficient overall. Again,,, part of why is you simply get up the mountain a few mph slower. You can see that you are pulling less watts at max speed up the grade, and you should, you are going about 2 mph slower. But when you watch the motor with a heat gun or internal thermometer, you do see the low rpm motor running cooler when you top out. This hill is 5 miles, the last two miles 7-8% grade.
That is a cooler motor up the hill, when all else was the same. Same hill, same weight, same controller, same battery, same weather.
It's a big hill, and measuring the wh taken to get to the top, the difference is really quite small. Its a mountain, and you never get up it cheap. It's about 50w less to the top using the slower motor. Sounds like not much, and it's indeed it's not much. But 50wh worth of less motor heating can be crucial. With 50 miles with no water, no plugs, nothing but burning desert on the other side of that mountain, 50 wh more range on the other side is mighty nice. It might mean pedaling the last two or three miles to a plug, or not. But most don't try to ride an ebike across a desert like that. So the 50 wh usually does not matter at all.
You are incorrect that slow climbing speeds with slower-wind motor are better. Slow speed climb ALWAYS destroys efficiency, because you "spend" more time with phase-currents to fight gravity...
You can compare it to starting to cycle from stand-still when you are stuck at high-gear. At start, your legs are very inefficient as our legs have very narrow efficient RPM zone, but once you get to speed - you accelerate swiftly. During the too slow RPM's, you are mostly converting your muscle's work into heat. That's what's going on inside your motor when it's going too slow, and against a big torque load.
It's also the same like pedalling uphill, but at a bit high gear - you would want to speed up so the RPM of your legs will increase.