Giant hub motor vs mid-drive efficiency.

Can you get similar efficiency to a mid-drive if the hub motor is powerful enough?


Are hub motors losses largely copper or does magnetic saturation of the stator cause greater hysteresis in the core? and si

Im fairly certain you can find some mid drive motors that are more efficient than some hub motors.
..but also the reverse applies. !
Unless you are considering identical motors, its an impossible comparison.....but then one of them wont be optimised for its application.
However, a mid drive will always have some extra transmission losses that a hub motor doesnt incurr.

Watt for watt, and speed matched, a direct drive hub motor is more efficient than a mid drive, due to no transmission or gearing losses. This assumes the DD hub uses a winding that is properly paired with voltage, wheel size and controller current.

When u say properly paired with the voltage, wheel size, and current. It's a skateboard hub motor with a 4770 stator using 50 volts and I've seen 50 amps peak


It's a hub motor direct drive and long. The diameter of the wheel is 80mm. Longboard wheel size. Small long wheel. 80x101. I'm wondering how it will do as typically I hear complaints that hub motors suck a lot more amps with a large load.

Looking at this these an explaination in which the mid drive can select an ideal rpm for best power or efficiency but what of a situation in which the mid-drive has one gear only? The mid drive would simply be able to move quicker toward the right of the graph but have the same percent of time spent in any of the zones. What am I missing?

http://clevercycles.com/blog/2005/07/31/motors-and-bicycles/

Maybe since a hub motor must have more turns and greater resistance to get the torque as a geared motor?
Maybe a large hub motor with as low a resistance as a geared motor..be as good? But likely then not as good with low load since increased iron losses an noload current ?

What is the most efficient hub motor for sale?

wesnewell said:

At 1-7.9 mph on a 3% grade it never overheats. At 8.1 -11.1 mph it takes an hour to overheat. so the slower the better, but efficiency drops the slower you go. only 66% at 8 mph. At 11 mph it's over 71%, which is the slowest I'd want to ride it for any distance. By comparison, the H3540 motor will always overheat in a short distance with a lot less efficiency. At 8 mph it overheats in 15 minutes with only 53% efficiency.

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Why is one hub motor more efficient at slow speeds? What makes a hub motor efficient?

Hummina Shadeeba said:

wesnewell said:

At 1-7.9 mph on a 3% grade it never overheats. At 8.1 -11.1 mph it takes an hour to overheat. so the slower the better, but efficiency drops the slower you go. only 66% at 8 mph. At 11 mph it's over 71%, which is the slowest I'd want to ride it for any distance. By comparison, the H3540 motor will always overheat in a short distance with a lot less efficiency. At 8 mph it overheats in 15 minutes with only 53% efficiency.

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Why is one hub motor more efficient at slow speeds? What makes a hub motor efficient?

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The way the windings are made - size, number of turns, even the topology.

All motors have a maximum unloaded speed. The further you are away from this speed, the more energy you waste, hence lower efficiency.

Hummina Shadeeba said:

Why is one hub motor more efficient at slow speeds? What makes a hub motor efficient?

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I slower wind motor (lower Kv rating) is more efficient at slower speeds. The 6T mxus 3000 is rated at 6Kv, while the H3540 is rated at ~9-10Kv. At the same voltage the slower wind motor won't waste as much energy to heat loss as a faster wind motor and provides more power. The higher number of winds on each pole provide a greater electromagnetic force per pole, thus making them more efficient at slower speeds. There's probably a better way to explain it, but that's all I've got.
https://www.youtube.com/watch?v=uLutMoh4Ttg

Is there any way around the inefficiency of an electric motor at the lower rpms? I'd like to have my hub motor wound to 90kv which nets me 30mph on flats but the inefficiency at low speed is a drawback. Is it a purely mechanical reason for the inefficiency and the speed just isn't there yet regardless of the size or design of the motor?

I read more poles can give greater low speed torque...will that equate to greater efficiency at low speeds than a fewer poled motor?

A 90Kv hub motor @ 50V is 4500 rpm. In a 26" wheel it would have an unloaded speed of 348 mph. Perhaps you meant 9Kv, not 90Kv.

wesnewell said:

A 90Kv hub motor @ 50V is 4500 rpm. In a 26" wheel it would have an unloaded speed of 348 mph. Perhaps you meant 9Kv, not 90Kv.

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I think he's making a skateboard instead of a bike.

I think there's some confusion here: we know winding configuration doesn't affect efficiency (assuming the same copper fill) and this doesn't suddenly stop being true at low speed. Motors can be efficient at low speeds, the problem is low speed situations often occur at high load, so losses will be high. Motor cooling is also reduced at low speeds and more heat = more resistance = more loss = more heat =...

Spinning a motor faster also isn't automatically good for efficiency: efficiency at no load speed is 0%.

I have no idea what would be ideal for a board. But I can speak from experience with bikes.

Hub motors only get bad inefficient when they are overloaded. Mid drive has the advantage, of being able to shift to lower gears when overloaded.

At some point with either, there is a sweet spot where efficiency is less, but not so bad you overheat shit, and there is decent power to do what you need. A combination of load and rpm. Time to overheat is one way to get a quick estimate of if it sucks bad, or is ok.

The key thing here is overloaded. kind of hard to overload a big enough hub motor, and you can set one permanently in a lower gear by using a smaller diameter wheel.

So as always, "it depends"

The catch 22 on a big powerful fast DD hubmotor is,, you will not get great watthours per mile hauling ass up hills loaded heavy. This is not to be confused with inefficiency. The motor CAN haul ass up the hill running at an efficient rpm. It just costs watts to weigh a vehicle down heavy, then haul ass, uphill, or even on the flat. You just have weight, and fast means wind resistance. Basic Mechanical Physics.

But take your big powerful hub motor in 26" bike wheel, and a typical bike and person weight under 300 pounds, and ride it 10 mph on the flat, and the motor is under so little load that it can get a great wh/mi compared to another, lower speed wind motor. The key thing here is that the big ass motor is never close to overloaded. And then you pedal, and the motor is barely ticking over going 10 mph. Your pedaling is putting out 75% of what you need, so of course the amount of your battery you use is tiny.

Sure,, if you always ride 10 mph, the lower speed wind does do a better efficiency, but not by a huge number, not by 20%. Maybe more like 5%. I am meaning the change in the wh/mi you use. The thing is, if you are pedaling up 75% of it, a relatively big change in the last 25% is still a damn tiny number. Overheat in 10 hours, overheat in 15 hours, what's the diff?

The key thing here, is the big motor is never overloaded. Obviously it's not overloaded on the flat, but on a big hill it's not overloaded either. If you can manage 15 mph up a huge mountain, you will still be turning that motor in a reasonably efficient rpm.

So that's it for hub motors. THE KEY THING IS DON'T OVERLOAD THE MOTOR. This is why I mentioned 300 pounds. Most 500w rated motors run on 1000w can get up a big hill just fine, with grades under 10%. You can overload the motor with both weight and grade, so increase either, and you might slow your max rpm enough to be overloaded.

People will argue what is overloaded, but my experience is that 500w rated hub motors start to suffer in 26" wheels when they can't climb a hill faster than 12-15 mph. This happens above 10% grades for a 200 pound man, on a bike that weighs 100 pounds including cargo.

This monster of a bike, loaded to 450 pounds, gets up 8% just fine, at 15 mph. It had a big crystalyte motor able to run at 33 mph on 48v 40 amps. Yet it could also get a very nice watt hours per mile while going 15 mph on the flat. Good enough efficiency for an 80 mile day.View attachment 1

Now,, you want to really improve the efficiency of a DD motor, make the wheel smaller. That is the big reason I don't ride that monster bike anymore. The next bike I made for touring is this one. The 20" wheel is slower, so more efficient, but it's also more able to get up a hill efficient, with a big load, because it's simply in a lower gear.

thanks for all the info.
so a hub motor has two obstacles to ultimate efficiency, one being it's out of it's ideal rpm and two being it can be overloaded in such a situation and further be inefficient. a bigger hub motor being more able to avoid overload at least

Hummina Shadeeba said:

so a [strike]hub[/strike] motor has two obstacles to ultimate efficiency, one being it's out of it's ideal rpm and two being it can be overloaded in such a situation and further be inefficient. a bigger [strike]hub[/strike] motor being more able to avoid overload at least

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The edited quote above with the word "hub" stricken from it is more correct, because it doesn't matter whether the motor is in a hub or not, the statement still applies, to all motors.

True, AW. But once it's a hub motor, it does get harder to do anything about a mis match of load and motor size. Only way to gear down a hub motor is make the wheel smaller. That may or may not be possible, or practical to do on a particular vehicle.

Don't know whether this will illuminate or obfuscate the subject, and is probably too low-power for ES, but my friend and I rode up an 8 mile 3000' ascent together pedaling moderately and of similar fitness in about 50 minutes (didn't measure exactly) together. He (148 pounds) was riding a 2015 Felt hardtail (41 pounds) with a Bosch mid-drive and I (180 pounds) was on a E-Motion two-wheel drive EVO (57 pounds). He used about 80% of a 396 a/h battery and I used 87% of the same size one (or so).

I've been hearing conflicting info on if more poles can equate to greater torque though. On this forum I've read a motor with more poles will create more torque, and therefore I assume it will also be more efficient in a slow moving heavily loaded situation, but then I wrote to two guy who wrote a book on brushless motors and was initially looking to get some design consulting but they pretty much said it wasn't worth it to alter the stator from 12 to 24 teeth as it would only allow the slightest increase in torque as the back iron can be a bit thinner so the airgap diameter is a hair wider, but that was it. Please throw in your thoughts. Ive been selling these little hub motors for skateboards I designed but I skipped the magnetic aspect of it and was just concerned with the mechanical. I've been using a 12 tooth with 14 poles but since I'm so far from the max erpm the esc can handle it's possible to go with the greater amount of poles no problem, which would give maybe a smoother motion at slowest speeds, but will it actually then be able to produce greater torque and therefore greater efficiency at lower speed? Is there an ebike equivalent? I see so many poles in all the ebike motors.
steelhubs.com you can see the old ones I sold. the new are with a double length stator but the same design really and still 12 tooth. Ive done some simulations on emetor but they don't seem to be right.

also have you found sensors to improve efficiency much?