Question I couldn't answer ...

[danfoto]

I came out of Tesco's this morning and got into conversation with an old boy about electric bikes, and he asked a question I couldn't answer.

If you ignore both cost and the ability to retro-fit to an existing unpowered bike, is there any case or circumstance in which a hub motor has any advantage over a crank motor?

 

[flecc]

Yes, in moderate territory I think a hub motor is the best choice. It's relatively simple and easy to service in a way that crank drives never are, and it doesn't wear the bike's transmission. In the event of failure outside warranty, the replacement cost is much lower than a crank drive unit. The controller is separate so a failed one can be replaced at moderate cost. Crank drive units have them integrated and sometimes not replaceable.

Crank drives come into their own on the steepest hills where the gearing down advantage for climbing is more useful.
.

 

[danfoto]

Just goes to show - we live in a hilly area, which both he and I consider to be the natural home of a crank-drive electric bicycle. It obviously didn't occur to either of us that we might think differently if we were in the Fens ...

 

[Deleted member 4366]

Just goes to show - we live in a hilly area, which both he and I consider to be the natural home of a crank-drive electric bicycle. It obviously didn't occur to either of us that we might think differently if we were in the Fens ...

You just need the right hub motor. The Bafang BPM or any similar motor will blitz any currently available crank drive in hill-climbing in any circumstances You don't even have to pedal if you don't want to. The advantage of the crank drive (in principle) is that it can use whatever power it has over a wider speed range.

You have to be more specific with which motors you're comparing, what hills your talking about, how fast you want to go and how much weight you have. You can't generalise.

 

[neptune]

I live in the fens . We don`t do that up and down stuff people keep talking about . So I am well happy with my hub motor equipped 2002 model Powabyke Euro with its well worn lead acid batteries . When God made the fens , he had bikes in mind . Its just a shame about the high average wind speeds . But I reckon that the wind turbines that are breeding like rabbits might help to cure that problem .

 

[Cyclezee]

You just need the right hub motor. The Bafang BPM or any similar motor will blitz any currently available crank drive in hill-climbing in any circumstances You don't even have to pedal if you don't want to. The advantage of the crank drive (in principle) is that it can use whatever power it has over a wider speed range.

You have to be more specific with which motors you're comparing, what hills your talking about, how fast you want to go and how much weight you have. You can't generalise.

I would add to d8veh's post with one word, eZee

 

[NRG]

Dont agree, IME on the very steepest of hills my PCS climbs far better than my two Bafang bikes. On flat and moderate stuff the Bafang's are preferable and require far less input from the rider. All hub motors are effectively stuck in top gear and unless you can keep a speed on hills thats approximately half the achievable assisted speed on the flat they become inefficient, bog down and progressively provide less assistance. In the case of a crank drive the rider has the ability to change the gear ratio and therefore provide a more efficient climbing speed for the motor,

 

[danfoto]

If you plot torque against road speed for this Bafang motor thingy, or indeed for your common or garden hub motor, what does the curve look like?

 

[flecc]

Torque maximum at zero revs, declining steadily to near half road speed and then falling away more rapidly.

Power zero at zero revs, rising steadily with speed and then crossing the torque line at around half road speed. Then declining from around two thirds speed.

Climbing ability optimal at that half road speed, but falling very rapidly as road speed falls below that.

Depending on rider strength, there's an incline hinge point beyond which a crank system will always beat a UK/EU legal hub motor.

 

[danfoto]

Torque maximum at zero revs, declining steadily to near half road speed and then falling away more rapidly.

Thank you flecc. I know I've only just had my second coffee, but even so I guess I'm having a brainfart here. By "road speed", do you mean max road speed to which the motor alone will drive the bike?

 

[flecc]

Yes, basically the legal cutoff speed of about 15 mph..

Typically the optimum climb speed is about 8 to 9 mph. Fall below 8 mph and the ability declines quite rapidly with speed reduction.

(Three coffees answer!)

 

[mike killay]

I regularly climb a 1 in 9 on my Tonaro crank driver. Normally I climb in second gear with light pedalling. The speed is 5.8mph. As this is a busy, narrow main road, I ride on the very narrow footpath. I would not want to go faster because of hazards like overgrowing bushes etc. Possibly a Bafang would 'Blitz' me, but could it go slowly up that hill under full control rather than a desperate headlong rush?
As an experiment, I stopped on the 1 in 9, put the bike into first gear, got ready, gave a mighty pedal and opened the throttle. The front wheel came off the ground. I stopped pedalling and the machine carried on up the hill on power alone at 3.4mph.

 

[Deleted member 4366]

Here's what a hub motor can do up a long 30% hill. Show me a crank drive that can do this:
https://www.youtube.com/watch?v=RIHJPOL3_HQ

 

[flecc]

That's the crank drive advantage Mike, full flexibility with hill climbing.

 

[flecc]

Here's what a hub motor can do up a long 30% hill. Show me a crank drive that can do this:
https://www.youtube.com/watch?v=RIHJPOL3_HQ

I only ever speak of UK/EU legal bikes in performance comments, since that's mainly what members own.

Some Cyclone crank drive motors can match that, also Stokemonkey and Optibike, but not legally here.
.

 

[indalo]

Show me a crank drive that can do this:

Why do you bother to offer stuff like that when it's clearly an illegal bike as far as the UK is concerned?

There's nothing smart or clever about attaching ridiculously powerful electric motors to bikes. Most people who require a little assistance to help them along on a bike want to be able to strike a balance between hill-climbing ability, decent mileage per charge and the peace of mind that goes with knowing the machine is legal. A local bike shop which carries or can get hold of spares quickly as well as offering repair and warranty work as required figure much higher for most ebikers.

Indalo

 

[Deleted member 4366]

I only ever speak of UK/EU legal bikes in performance comments, since that's mainly what members own.

Some Cyclone crank drive motors can match that, also Stokemonkey and Optibike, but not legally here.
.

They'd bust the chain on that hill!

 

[flecc]

They'd bust the chain on that hill!

. It would certainly give it a tough time!

Not bust it though, member Fecn and I have ridden 1 in 3.3 on Agattus which suffered no chain problems then or subsequently, admittedly with less power and speed of course. They can wheelie from a standstill too.

 

[Deleted member 4366]

Why do you bother to offer stuff like that when it's clearly an illegal bike as far as the UK is concerned?

There's nothing smart or clever about attaching ridiculously powerful electric motors to bikes. Most people who require a little assistance to help them along on a bike want to be able to strike a balance between hill-climbing ability, decent mileage per charge and the peace of mind that goes with knowing the machine is legal. A local bike shop which carries or can get hold of spares quickly as well as offering repair and warranty work as required figure much higher for most ebikers.

Indalo

• I'm answering the question that the OP posed, where he was discussing which type of motor climbs best. I'm merely answering the question
• The regulations might change soon to make these motors allowable, so that would also increase the relevance of the post.
• This is an open forum, where people should be able to explain technical matters freely and without censure. Whether somebody wants long or short battery life, or whether they want to have a bike that doesn't comply with regulations is their personal choice and not for you and me to judge (unless you're a policeman, magistrate or judge).

BTW I think it's wrong to make sweeping statements about what most people want. When you say "most people" do you mean 50.001% of the population, or do you have a different number in mind? How many were in your survey and was it representative of the whole population?

That MAC motor isn't particularly powerful. I think 1500w was quoted, which is twice what most shop-sold UK hub motors have.

 

[flecc]

That MAC motor isn't particularly powerful. I think 1500w was quoted, which is twice what most shop-sold UK hub motors have.

That's bit like telling the magistrates "But I was only doing 140 mph on the M1 your worships".