Counter intuitive power-assistance response

[ambodach]

I have a GTech Sport. I have discovered that on hills if I keep pedalling hard I do get some sort of assistance from the motor but not much particularly on steep hills and I really struggle to get to the top and speed falls to about 5 or 6 mph even with hard pedalling. If I ease off on pedalling pressure a bit earlier and let the speed drop to about 10 or 11 mph I get a “push” from the motor. You have to have the confidence to let the pedalling pressure drop a bit to get any real assistance. Sounds weird and not how you would expect things to work. Hope this makes sense to somebody. Any comments?

[Cyril Haearn]

How would you expect it to work? Are you over-thinking? Or is the machine over-thinking?

[ambodach]

I may be overthinking but I would expect to get more push from the motor when things were getting a bit tough rather than less as appears to be the case. Even on gentle hills I can make the motor kick in with more power by simply easing off on my effort.It needs a bit of confidence that it is going to work but it is the opposite of what I do on any ordinary bike. Come to a hill and increase the effort is what anyone would normally do. How do other electric assist bikes work?

[kwackers]

Don't know about that bike but mine has a cadence fall off range as well as speed.
So if you peddle 'hard' you do most of the work, let the cadence fall a bit and the motor does most of the work.
On level 5 you have to peddle like a demon before the motor stops assisting!

[stodd]

The problem with hub motors (or bottom bracket motors if no gears) is that the motor is revving at low speeds on hills, so unfortunately can provide less power than on the flat, even though more power is needed. This is specially awkward on a bike with no gears as you can't use the gears to keep your cadence up on hills either.

[ambodach]

kwackers my problem sounds very like as you describe. The GTech is a single speed belt drive so there is no option to change gear. Power levels are — off,full and half so not much choice there either. It is a good bike for some purposes but not really an allrounder.

[Col18]

Hi

I have a similar bike, I bought from Aerotek, it has SRAM Automatix hub gear. This has 2 gear.
Hub motor on the front, is pedal assist only, just cadence sensor, its basic, no throttle, no LCD display etc.

My commute route is mainly flat with 3-4 slopes, steepest is about 6-7% but all not to long slopes.

I think both bikes are similar, as you approach the 15mph, the motor assistance ramps away.
So when I cycle up hill, with the weight of battery and motor it almost pointless to pedal faster than 15mph as it will take a lot of effort, especially for you as you have only 1 gear.

I either pedal with medium or low effort and let the motor do most of the work, as that what I got the bike for, to get me over the hills.
Going up longest and steepest hill the speed drops to 9-10 mph, with medium effort.
And about 8mph with low effort, ie lower cadence. (But I have energy in the legs to carry on after going over the top)

I have done a test run when I first got the bike, there is a steep hill, 10% at about 60m and the speed slowed down to about 5-6mph, but it was easier and quicker than spinning on the lowest gear on a mountain bike. Until I stopped and tried to start pedaling up the hill again.

[ambodach]

Stodd seems to have a reason for my problem. Trouble is there seems no way to increase motor revs to keep the power up on hills. If I ease off on pedal revs within limits I seem to get more power but that seems a bit daft.
Starting on hills is another ball game but without spending loads of money is just something you have to try to avoid I think.

[stodd]

Just to clarify my last reply and Col18's. Power will fall off at both ends of the speed spectrum.
* low speeds (as I mentioned) as even with high torque you are not getting much power
* higher speeds (approaching 15mph) because of the nature of motors and the artificial 15 mph legal limit applied by the controller.

For us (a bit older and living in hillier but not very hilly areas) the top limit is mostly irrelevant, and certainly irrelevant on hills. The lack of low speed power is what matters: we have to keep to a low gear and pedal significantly to get up a 12-15% hill on our tandem with fairly low torque motor (****). Still very worthwhile having the motor, as we get to the top of the hill somewhat exercised but much less knackered.

For you, it makes sense that you are getting most power around 10 or 11mph, and if the bike can manage that on your hills with relatively little power from you that will be easiest. Going faster will require more power, and the motor will provide less, so you will need to provide much more. The real problem will come if you hit steeper hills: you will then be in the same position as us (except + without the weight of two people and - without the help of gears). The motor will not be able to push you up the hill unaided or with just a small effort from you, you will have to pedal significantly.

(***) We were warned by Woosh about the disadvantages of the lower torque motor, but a combination of availability and other tradeoffs made us go for it anyway, and we are happy with the compromise.

[ambodach]

Thanks for that stodd. Very helpful.