Hub motor vs Mid drive (efficiency)

[michael.kozera]

Hub motor vs Mid drive strictly from an efficiency stand point, ( how far can you go on a charge).

I own and ride both, and from my experience ive noticed that hub drive is about 30% more efficient over all when compared to mid drive assuming all else is the same. wind, grade, tires, weight, assist amount, etc, etc.

however, ive seen many posts and videos of people claiming that mid drive is both more powerful and more efficient. interestingly however, they never back their claims with any real scientific testing or real world examples. just abunch of butt-dynos and % screen readers, ( and we all know how accurate % read outs are on e-mtb's).



As an engineer, i have thought about this extensively. most hub motors have around a 9 to 1 reduction ratio, and the power goes straight into the wheel. while with mid drive you have around a 30 to 1 reduction ratio + the bikes drive train. so you should have significantly more power loss with a mid drive. however the mid drive can take advantage of the bikes gearing to give more wheel TQ, which would be better for steep stuff.......



so i plan on doing a very comprehensive test with two bikes , one mid, one hub drive and use identical tires, pressures, weight, power, rider, etc,etc. i want to do 100w, 250w, and 500w at various speeds, grades, and gears, no pedaling just a thumb throttle to take the rider completely out of the equation. a precision watt-meter, gps will give accurate results.

i suspect that on faster flatter roads the hub motor will be significantly more efficient, but on very hilly stuff the mid drive will be more efficient. the question is, by how much? and once normalized, on average, how much more efficient is one vs the other.



ill post my findings here shortly.

thoughts?

has this been done already?

 

[Zimmerframe]

however the mid drive can take advantage of the bikes gearing to give more wheel TQ, which would be better for steep stuff.

It's an interesting question. As you say there probably isn't an all round definitive answer. One is better in some situations than the other.

A hub drive has some advantages, like you're not having to transmit all the power through the chain and gears which were ultimately designed for human power - so you're reducing wear and strain.

On the bikes I've ridden, weight distribution is noticable with a hubdrive for me - so I'm not sure if you add that in as a factor relating to rideability as a factor with efficiency ? It's a factor which will affect different riders on different terrain in different ways. I think you should also test a two wheel drive setup with smaller motors

One other noticable thing for me on most hub drive bikes is that the torque sensor generally isn't as effective/responsive as the setup on most mid drive bikes.

 

[Mabman]

I also have bikes with hub and mid drives. I far prefer the hub motors for primarily road use and mid drives for off road use. Based on wh/mi seat of the pants observations I have made over the years it is much easier to achieve low wh/mi with a hub motor than a mid drive for road riding when I set up two bikes in a similar fashion a few years ago. But as most of my rides include road/trail/gnarl I find myself riding my mid drive mtb the most. Soon I have to be in the city for a month and a half and am prepping my hub bike for use there as in the past it has worked the best in that environment.

 

[Neeko DeVinchi]

Its been a while since I've swung a leg over a hub powered ebike. But I do remember that their are two types of hub motors
(Geared & Gearless Direct Drive).

Which type of motor are you expressing an interest in ascertaining the efficiency @michael.kozera ?

 

[michael.kozera]

ok, numbers are in:


both bikes i used throttle only with a throttle lock to get super consistent wattage's, i used a 200a precision watt meter, and i used GPS to calibrate the speed displayed on the ebike screen.


for this test i used a bbshd mid drive with a 42t front, and the other bike was a hub motor (750w casing, geared planetary). both bikes had identical all terrain tires, at exactly 30/35psi F/R. both bikes weighed the exact same. i did not use the pedals at all for any of the tests, throttle only.



for the mid drive, H= small rear gear (11t), M= middle cassette gear (25t). L= largest rear gear (52t)

flat ground 100w:
hub motor got to and maintained 18km/hr
mid drive got to and maintained L=20km/hr, M= 17km/hr, H=15 km/hr
250w:
Hub =29km/hr
MID L= n/a (20km/hr, wheel wont spin any faster) , M=25km/hr , H=23km/hr



slightly hilly 100w:
Hub= 8km/hr
mid L=11km/hr , M=5km/hr, H n/a (not enough power to move)
250w:
Hub= 14km/hr
Mid L=13km/hr, M= 9km/hr, H5km/hr


very hilly/steep 100w:
Hub= n/a (not enough power to move)
Mid L= 3km/hr, M=1km/hr, H=n/a (not enough power to move)
250w:
Hub=3km/hr
Mid L=10km/hr, M=6km/hr, H=n/a (not enough power to move)
750w:
Hub=7km/hr
Mid L=15km/hr, M=12km/hr, H= 3km/hr

slight Downhill 100w:
Hub= 42km/hr
Mid=39km/hr


extremely dirty chain test 250w:
Hub=n/a
MID L= n/a (20km/hr, wheel wont spin any faster) , M=25km/hr , H=23km/hr

Hot motor test, aprox 60c, flat ground, 250w:
Hub=27km/hr
MID L= n/a (20km/hr, wheel wont spin any faster) , M=24km/hr , H=22km/hr



Last test, average typical ride real world test:
mix of about 40% flat, 40% slightly hilly, 10% very steep, 10% down hill. both hub motor and mid drive was set to 220w of continuous power, and mid drive gears were shifted to keep it in the most optimal rpm/speed, but i kept it as close to the middle of the cassette as i could (25t).

Hub motor used 264.4wh
Mid drive used 298.5wh

 

[michael.kozera]

conclusion:

the total system efficiency depends on what ur riding up.

for example:
at 250w on flat ground, a hub drive is approx 31-to-15% more efficient then a mid drive lets just call it 20%

at 250w on slightly hill, a hub drive is approx 62-to-5% more efficient then a mid drive lets just call it 30%

at 100w down hill, a hub drive is 8% more efficient then a mid drive.


but......on the other hand;
at 250/750w on very steep hills, a mid-drive is approx 70-to-56% more efficient then a hub drive lets just call it 60%


motor heat seemed to have made more of a negative impact on the hub motor then the mid drive, probably because the mid drive the motor coils are on the outer part of the can, getting direct cooling, while the hub motor the coils are on the inside of the hub not in direct contact with the outer aluminum can cooling. however, heat didnt make that much difference, about 5%

dirty chain ( caked in sand and mud and sticky grass) ,really surprised me, no observable difference in performance, less the 1% probably. strange as i thought this would have a much larger effect.


the real world test was a good example of total system efficiency across many usages/ grades. as it appears a hub motor is about 11% more efficient then mid drive. the ride i did is what i would consider a modest average ride through a city, for the average person.

but i bet you if you added more hills into the mix, the mid drive would out preform the hub drive in efficiency.

or vice-vera, if you were riding on flat ground, the hub drive would be significantly better.


so end of the day it really is Mid-drive= off road, Hub drive = on road. its really that simple !

 

[Alexbn921]

Nice test. Thanks

 

[Mabman]

"so end of the day it really is Mid-drive= off road, Hub drive = on road. its really that simple !"

I came to this same conclusion a number of years ago. However it still seems like the "major" manufacturers don't agree and stick a mid drive on everything pretty much? Road or MTB.

Personally I don't use any PAS with my 1000w front hub DD bikes. I prefer to use a throttle activated "cruise control" feature that allows me to set my wattage and then pedal/shift away as one normally would with the motor providing constant momentum. But for MTB use a good torque sensing PAS is preferred.