Electric Bike, Power, Relative Overall Efficiency

Electrically assisted bikes, trikes, etc. that are legal in the UK
Carlton green
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Electric Bike, Power, Relative Overall Efficiency

Post by Carlton green »

I’m wondering if there is any helpful data on the overall efficiency of electric bike power trains. Efficiency being: mechanical power out divided by electrical power in. Power being measured in Watts. What is also important to me is efficiency at various road speeds (zero mph and then up to the legal powered limit).

The power trains that I see at the moment are: front hub drive, rear hub drive and crank drive. No doubt what I ask isn’t straight forward but it’s a start point, my thanks in anticipation of your responses.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
Bonzo Banana
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Bonzo Banana »

I think the common term used is watt hours per kilometre and the lowest I've seen was 6Wh/Km which was a small geared hub motor with the clutch disabled and regen enabled. I guess the average figure is around 10 Wh/Km. There is a basic rule that you divide the battery capacity by 10 to give the rough guide to distance in kilometres. So if you have a 600Wh battery you can expect around 60km of range or around 40 miles. It should be pointed out hub motors are separated into two types direct drive and geared. The efficiency between all 3 motor systems is actually very comparable with a lot of overlap its all down to implementation really and how you ride.
Jdsk
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Jdsk »

Carlton green wrote: 16 May 2022, 2:46pmEfficiency being: mechanical power out divided by electrical power in.
Bonzo Banana wrote: 17 May 2022, 6:50am I think the common term used is watt hours per kilometre and the lowest I've seen was 6Wh/Km which was a small geared hub motor with the clutch disabled and regen enabled.
Energy/distance is commonly used in the eBike world. The problem is that there are two different properties (energy/distance and *power /power) being given the same label: efficiency. This is obviously likely to cause confusion.

Jonathan

* Power/power is the same as energy/energy in this context as long as you define the time of the study (or integrate appropriately) and aren't storing any energy anywhere else.
Carlton green
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Carlton green »

All the info that I can find seems like ‘smoke and mirrors’ to me, perhaps something helpful will emerge in time. There’s lots of aftermarket stuff that you could fit and one could easily get confused by it all … and waste a bundle of money too. I guess it’s just one of those things to keep an eye on and see what emerges … and then there is after sales support or lack of it. I’m fine without assistance at the moment but if I needed it then, for me, I’d be looking (first) towards a geared front hub. The swytch kit seems popular and I guess that it’s reasonably easy to install.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
Manc33
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Manc33 »

Carlton green wrote: 17 May 2022, 2:51pmI’d be looking (first) towards a geared front hub.
Why a front hub and not a rear?

My setup has 5 power levels. On level 1 it goes about 9 MPH on the flat and I'd probably get about 60 or 70 miles out of it (that's from my 1,140 Wh battery). Even though on level 1 I am pedaling using my own leg power most of the time, it's not as efficient as I thought it should be - maybe because the motor is simply working for a longer amount of time, since I'm going at only 9 MPH.

On level 2 (12.5 MPH) it goes about 50 miles. On level 3 (15 MPH) about 40-45 miles.

Level 4 and 5, I never bother with (unless it's hammering it down or I'm out late and want to get back home).

The "smoke and mirrors" you speak of is probably down to the amount of variables there are?

- Tyre width.
- Tyre brand.
- Tyre pressure.
- Battery voltage.
- Bike weight.
- Rider weight.
- Your effort.
- Wind.
- Hills.

I have no doubt missed several other things off the list.

The only thing I ever saw that tried to give figures was that Bosch website, but those figures vary wildly and they relate to Bosch motors... which I haven't got (it's a Bafang rear hub) so none of it applies to me.
We'll always be together, together on electric bikes.
axel_knutt
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by axel_knutt »

Bonzo Banana wrote: 17 May 2022, 6:50am I think the common term used is watt hours per kilometre and the lowest I've seen was 6Wh/Km which was a small geared hub motor with the clutch disabled and regen enabled.
There's little point in measuring efficiency as distance/energy because that depends on the effort supplied by the riders legs. Taking the output as being the motor including any transmission not common to the riders legs would be the proper place to measure the efficiency of the assist system alone, but if comparing complete bikes, then all the factors applicable to non-assisted bikes (wind & rolling resistance, weight etc) would also be relevant.
“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
― Friedrich Nietzsche
Carlton green
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Carlton green »

axel_knutt wrote: 17 May 2022, 4:12pm
Bonzo Banana wrote: 17 May 2022, 6:50am I think the common term used is watt hours per kilometre and the lowest I've seen was 6Wh/Km which was a small geared hub motor with the clutch disabled and regen enabled.
There's little point in measuring efficiency as distance/energy because that depends on the effort supplied by the riders legs. Taking the output as being the motor including any transmission not common to the riders legs would be the proper place to measure the efficiency of the assist system alone,
That’s my take on things too.
Why a front hub and not a rear?
Independence of power application comes to mind. Rear hub would be my second choice and mid positioned being my third preference. I have no wish to mess with a rear hub without good reason and even less wish to push power through chains, sprockets and hub gears that weren’t built with that in mind. With mid drives you also appear to be limited to their single ring (circa 42t) on the crankset and some of them have questions about their gearbox robustness under load. However, that’s just my perspective at this point in time and I’m asking questions to learn.
The "smoke and mirrors" you speak of is probably down to the amount of variables there are?

Not really, I’m just looking for power out at the drive shaft and power in from the battery.

… wonder what happened to the formatting, electronics!
Last edited by Carlton green on 18 May 2022, 6:14am, edited 1 time in total.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
Bonzo Banana
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Bonzo Banana »

axel_knutt wrote: 17 May 2022, 4:12pm
Bonzo Banana wrote: 17 May 2022, 6:50am I think the common term used is watt hours per kilometre and the lowest I've seen was 6Wh/Km which was a small geared hub motor with the clutch disabled and regen enabled.
There's little point in measuring efficiency as distance/energy because that depends on the effort supplied by the riders legs. Taking the output as being the motor including any transmission not common to the riders legs would be the proper place to measure the efficiency of the assist system alone, but if comparing complete bikes, then all the factors applicable to non-assisted bikes (wind & rolling resistance, weight etc) would also be relevant.
Thats always the situation with ebikes and many ebike brands push up the claimed distance per charge to help sell the product which really can only be achieved by a light rider who likes to do a lot of the work themselves. However still you can give a rough guide to distance based on average use. On a direct drive hub motor ebike you can use your own power on the flats, use regen down the hills and use battery power up the hills and in theory could get maybe 200 miles out of a charge on a reasonable size battery but that wouldn't be normal use for most people. In theory you could get even more out of light geared hub motor ebike where you only use power for the steeper hills and use it as a standard bike most of the time.
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Cugel
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Cugel »

Carlton green wrote: 17 May 2022, 4:21pm (snip)

Independence of power application comes to mind. Rear hub would be my second choice and mid positioned being my third preference. I have no wish to mess with a rear hub without good reason and even less wish to push power through chains, sprockets and hub gears that weren’t built with that in mind. With mid drives you also appear to be limited to their single ring (circa 42t) on the crankset and some of them have questions about their gearbox robustness under load. However, that’s just my perspective at this point in time and I’m asking questions to learn.

(snip)
All e-bike motor configurations have their advantages and disadvantages. Which system one chooses will depend on the aspects of a bike and its behaviours that are most relevant to a particular rider.

Front hubs have the reputation of interfering adversely with the handling of a bike. They also seem to come with batteries that have to be hung or otherwise clagged to the bike externally, often high up so that handling is further degraded by raising the bikes centre of gravity. But they're easy to fit. The wheel can be got out without too much extra bother - although you can't swap to a different wheelset without including another hub motor.

Rear hubs are unobtrusive and are said to give a better feel in that their "push" is identical in placement (the rear tyre) to the push from the pedalling rider, unlike a front hub. But wheel change and puncture mending gets rather involved. They also tend to have a smallish torque (40Nm rather than 60 or 80).

There are several varieties of mid-motor. They can often improve handling by lowering the centre of gravity and most (not all) come with a frame-hidden battery. Your remark that you have " ....even less wish to push power through chains, sprockets and hub gears that weren’t built with that in mind" ignores the fact that the chains, sprockets and hub gears were designed precisely to handle power put through them. Many fit cyclists can put a continuous 200 - 250 watts through their gearing and those racing fellows can put up to 1400 watts momentarily through the transmission during a professional race sprint! Good time trialists often generate a continuous 300 or more watts for hours at a time.

********

The system that seems the most closely designed to emulate and enhance the cyclist's own effort is the Fazua system. The motor and battery are a removable module (consisting itself of two separable modules, motor & battery) that allows the bike to become an ordinary bike. The only irremovable e-bike part is the bottom bracket gear box ) just over 1 kg) built like a tank and apparently very efficient at transferring not just the motor power but also the cyclist's own pedalling power, going by my own experience using it. Even with the motor in and not working, the bike goes as well as or better than any 13 Kg tourer, with no drag at all from the e-gubbins.

https://old.fazua.com/en/drive-system/evation/

If the motor is used, the software blends its invocation with the rider's own efforts, which must increase to increase the motor help. No rider-effort, no motor power.

At present I ride such a Fazua-equipped bike without the motor and battery module in it. The gap where those go is filled by an identical casing that also serves as a large carrier for tubes, tools and cake, if you like. The bike weighs exactly 10 kg without the motor-module in it. It also uses a standard ISIS chainset and a standard everything else, all changeable to other standard components. No tie-in to a single ring of a particular tooth count or any other particular chainset.

It goes like a rocket with just me pedalling it. I'll readily agree that many of the more tank-like mid-motor e-bikes are unlikely to behave in this way. On the other hand, they can easily pass me going up the 300 metre climbs, with a load of luggage attached and the rider's chatting away happily as I gasp for the next lungful of go-gas. :-)

Cugel, trying to remain motor-unseduced.
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Carlton green
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Carlton green »

Many thanks for your insights Cugel, much appreciated.

Yep, each system has its pros and cons. Additional information is always good for our education and that was what I sought when starting the thread, unfortunately there seems to be no clear data on which drive types are most energy efficient but perhaps something will turn up later. In the meantime I’ll put a few more pennies into the piggy bank and I’ll lower the gears on my utility bike (via a smaller chain wheel).

Eventually a better way will become clear but in the meantime the exercise is good for me, perhaps :shock: . The journeys might take a little longer but that’ll be OK for a few years to come :) , but eventually a little motorised help will most likely be needed and I want to be ready for that time.
Don’t fret, it’s OK to: ride a simple old bike; ride slowly, walk, rest and admire the view; ride off-road; ride in your raincoat; ride by yourself; ride in the dark; and ride one hundred yards or one hundred miles. Your bike and your choices to suit you.
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Cugel
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Cugel »

Carlton green wrote: 18 May 2022, 1:30pm Many thanks for your insights Cugel, much appreciated.

Yep, each system has its pros and cons. Additional information is always good for our education and that was what I sought when starting the thread, unfortunately there seems to be no clear data on which drive types are most energy efficient but perhaps something will turn up later. In the meantime I’ll put a few more pennies into the piggy bank and I’ll lower the gears on my utility bike (via a smaller chain wheel).

Eventually a better way will become clear but in the meantime the exercise is good for me, perhaps :shock: . The journeys might take a little longer but that’ll be OK for a few years to come :) , but eventually a little motorised help will most likely be needed and I want to be ready for that time.
At 73 , my ole body is beginning to mention that it isn't as hardy as it once was. However, I know one old cyclist of 83 who can still out-pace me, on the flat at least, with no sign of him wanting a motor or anything else other than his legs and a proper bike. The rascal even has an artificial hip and still goes better than me!

So, I can't have a motor in me bicycle if he's still without one, can I? Even if there's space for one. If he drops dead on a climb, trying to hang on to an uppity sprog, I might be able to get that motor out of the cupboard. While he still lives, I couldn't bear the shame of riding assisted as his old pistons send him along half-wheeling me anyway. No.

Also, the ladywife insists that she should have the sole advantage of a motor so she can still beat me up the long steep drag to Troed y Rhiw for the village sign. :-)

Cugel, resisting electrified temptations.
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
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richtea99
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by richtea99 »

Cugel wrote: 18 May 2022, 11:07am Rear hubs .... But wheel change and puncture mending gets rather involved.
A slight aside, but I feel bound to puncture (ha) that myth.
It depends on the design. My ebikemotion rear wheel (Orbea Gain is the bike) takes all of 20s longer to remove compared to a standard rear wheel and maybe 30s extra to refit.

There are only three additional minor steps:
- unplug the motor cable
- remove the alignment washers
- on refitting only, align the flats on the rear axle to fit into the dropouts

The trick is to try it in the comfort of your own home, and not wait for a puncture in the wild to find out you don't know how it comes apart.

And back to the main discussion, another disadvantage to hub motors is that you cannot swap wheels.

Dare I ask the OP why the interest in efficiency? Is it for ecologic reasons (i.e. less waste)?
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Cugel
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by Cugel »

Perhaps the efficiency question is to do with matters of power-to-weight, mileage range and other aspects of getting the most go & distance for one's battery capacity, without just heating up a lot of the surrounding air with a battery/motor radiator? There's also the issue of how the various stresses and strains wear the parts, as one likes to be economically efficient to a degree (i.e. not have to scrap the old motor, battery or drivetrain for a new one every 932 miles).

I read and hear (on that Youboob) that hub motors are more prone to some kind of inefficiency because they have only a single gear, whereas BB motors have the bicycle's inherent gear system to ensure that the motor runs at an optimum rev at which it gives the greatest transfer of energy input to road thrust output albeit via a chainring, chain, sprocket et al. But I also read that electric motors care far less about the revs when delivering their power, so will work just as efficiently at low, mid or high revs.

Perhaps an electrical engineer could give us the troo facts on this feature of electric motors?

Personally I like the Fazua system as it gives a good torque (57Nm opposed to the 40Nm typical of hub motors) but mostly because it's a removable module, leaving an ordinary bike (except for the additional 1kg of the BB gearbox) when the battery/motor module is removed. The space even provides for an empty module case into which one can stuff tools, cake and even a raincoat! That modular design also enables easy battery charging off the bike; or battery and/or motor replacement if either ever go phut.

Perhaps this usability and ease of replacement, along with the easy transformation of the e-bike into a non e-bike, is another kind of efficiency?

Cugel
“Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist”.
John Maynard Keynes
stodd
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by stodd »

Carlton green wrote: 16 May 2022, 2:46pm I’m wondering if there is any helpful data on the overall efficiency of electric bike power trains. Efficiency being: mechanical power out divided by electrical power in. Power being measured in Watts. What is also important to me is efficiency at various road speeds (zero mph and then up to the legal powered limit).

The power trains that I see at the moment are: front hub drive, rear hub drive and crank drive. No doubt what I ask isn’t straight forward but it’s a start point, my thanks in anticipation of your responses.
There's lots of data at https://ebikes.ca/tools/simulator.html.
More on motor efficiency at various speeds rather than drive train, so you'd have to do quite a bit of extra work on their raw data/graphs to see the effects of the way crank drive motors benefit from the fact they take advantage of the gearing. Drive train .inefficiencies themselves are mostly smaller than the inefficiency from running a motor at the wrong speed.

Also mostly not that up to date so many modern motors are not there.
UpWrong
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Re: Electric Bike, Power, Relative Overall Efficiency

Post by UpWrong »

Bonzo Banana wrote: 17 May 2022, 6:50am I think the common term used is watt hours per kilometre and the lowest I've seen was 6Wh/Km which was a small geared hub motor with the clutch disabled and regen enabled. I guess the average figure is around 10 Wh/Km. There is a basic rule that you divide the battery capacity by 10 to give the rough guide to distance in kilometres. So if you have a 600Wh battery you can expect around 60km of range or around 40 miles. It should be pointed out hub motors are separated into two types direct drive and geared. The efficiency between all 3 motor systems is actually very comparable with a lot of overlap its all down to implementation really and how you ride.
So 10Wh/km, or 16Wh/mile for an electric bike. The best electric cars are around 250Wh/mile, so an electric bike is about 15 times more efficient than an electric car. Food for thought.
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