Hub motors and Hill climbers

[Phil the drill]

A few years ago I bought one of the first Powabyke 24spd commuter bikes - for just that purpose. It was very heavy (with SLA battery and steel frame), and a little pedestrian BUT despite it having only a nominal 200w motor, and weighing a ton it took my (considerable) bulk up some pretty wicked hills. Not fast, but without massive effort whilst carrying a pretty respectable load and with a decent range.
Can anyone explain to me why, several years on, many Kg's lighter, Li-ion fitted, 250w brushless motor equipped pedelecs STILL can't better it's performance significantly on steep hills, with big loads?
I currently own a wisper 905se, I love it, its comparatively light and much faster, but it still struggles to improve on steep hill climbing performance under load when campared with the old Powabyke. I have not ridden any other electric bike that can either - although truth be told I haven't tried many as they are very hard to come by in my neck of the woods.
Given that my perception is that most people buy 'electric' to help with the steep stuff, why has this not perceptibly improved? I wouldn't bother with an electric bike if I just rode on the flat or slight inclines to work - I'd save the money and complexity and buy a decent ordinary touring bike.
With all the claimed advances in weight saving and motor efficiency I have to say I'm a little disappointed in all the manufacturers. Everyone likes to knock the old Powabyke, but in my book none of them have that right until they can show how all their claimed efficiency improvements and light weight transfer into getting their fully loaded bike up hill (PROPER hills) significantly better than it did.

 

[flecc]

The answer is a combination of peak power and motor internal gearing Phil.

The nominal 200 watts of the traditional Powabyke motor disguises the fact that it's peak output is 700 watts, this due in part to the fact that these brush motors have a more "peaky" output characteristic than Hall effect motors which have wider power spreads instead.

The other factor is the fairly low internal gearing of the hub motor, giving just about 15 mph in the best conditions, but with the power peak at 7 mph.

Compare that with the new Torq example given by Wai Won Ching, same peak power output of 700 watts, but that peak torque/power at 11.2 mph.

It requires 60% more power to climb a hill at 11.2 mph than at 7 mph, so you can see that by being the Tortoise of the fable, the Powabyke can be a more able climber with the same power, where the Hare of the Torq gains in speed by comparison but doesn't do so well on steep hills.

The fact is that there are no miracles in electric motors, just different ways of using their power.
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[Phil the drill]

Thanks for the info. You certainly are a fount of knowledge!
I had not realised that the Powabyke had such a high peak power output. I guessed that the internal gearing must be partially responsible however. It would be nice if manufacturers could make information such as you gave more available to consumers. Knowing both peak power output, and particularly what sort of speeds these outputs are available at could be very useful to the potential purchaser - it would definitely help in deciding what sort of bike would be most appropriate for your particular type of use.

 

[flecc]

I fully agree Phil, getting technical information out of e-bike manufacturers is like trying to blood out of a stone and I've had to work hard at accumulating little shreds of information over years to know what I do.

The motor trade is a model in this respect, every scrap of information available on cars, and if only e-bike manufacturers realised it, they'd do their sales a world of good by being more open with information. Potential customers appreciate honesty and open disclosure.

As it stands, the e-bike industry is like the motor industry of the 1920s, and that's something for them to be really ashamed of.
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