Comment by jdboyd
3 days ago
In my city, travel habits and condition, I find I wish for more torque and lower speed. Every place I want to go has significant hills that the motor can't handle, and easing climbing hills is the main reason I want an ebike. My ebike's minimum speed for the motor is 15kph, which is ok by myself, but my family likes to go slower, so I have to go fully manual with them. When I look at ebike ads it feels like nobody else cares about these two areas of performance. When I talk to local ebike shops they are unprepared to talk about torque and minimum speed.
I fitted a Bafeng mid-drive motor to my city bike and it's fabulous for hills. Because the power goes through the existing drivechain you can get high torque simply by switching to first gear. No minimum speed, power kicks in after half a turn of the pedals. Coupled with hub gears you can change at rest it's a marvel.
Even at the European street legal limit of 250W it makes acceleration trivial.
It was too early and a bit of a dangerous design, but the StokeMonkey was built for torque and worked great at low speeds.
Some pedicab folks in Austin used to use them.
Hill climbing video YouTube https://share.google/iLrHXvjAKMO4esAux
Design info https://share.google/iLrHXvjAKMO4esAux
This is what gearing is for. Get an ebike with a mid-drive motor and some form of gearing -- a conventional derailleur, or an internally geared hub (Shimano makes a decent one, Rohloff makes a great one).
Internal gear hubs are pricy but great. I’ll strongly advise against a conventional derailleur with a mid-drive motor: the derailleur needs a thinner chain which wear faster, especially with a motor that apply more torque than a normal human. Internal hubs allow to use a 1s chain or better: a belt. Then you’re good to go for a loooong time. There’s also the (super expensive) Pignon mid drive with integrated speeds, a bit like the Schlumpf’s but for e-bikes.
Pro of derailleur’s e-bikes: their price.
[waited long time to do that] - a former bike mechanist
edit: the problem with faster wear isn’t the risk to break but the decease in efficiency which will affect your motor health (heating) and batterie capacity. If you’re on a budget there’s a compromise: find your favorite gear and replace the derailleur and cassette with a single speed front and back sprockets (and chain). Beware that might not be adapted to hilly roads as GP environment.
> thinner chain which wear faster
This gets repeated a lot, but isn't true. Cheaply made single-speed and 6/7/8 chains aren't any more robust than nice modern 10 and 11-speed chains. Shimano CUES (11-speed) works fine for ebikes.
Belts are fine, but less efficient than well-maintained chains. And they require special frames with some way of breaking the rear triangle.
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Exchanging torque and speed is like the only function of the gears on your bike.
Huh, it's you bike have a hub motor? The thing inside the wheel?
Mine sits between the pedals. That means I can just go down in gear and the motor helps with going up the hill.
Assuming it's a relatively cheap e-bike with a motor on the rear wheel (a hub motor), that's likely the motor being starved out of phase amps that create torque, rather than the motor being weak. Especially if it's large and heavy Direct Drive motor with no internal gearing. These need a strong controller (power supply) to feed them current, as voltage doesn't matter for torque.
But generally it's not the motor itself that's weak, it's just got a weak power supply (and potentially weak battery BMS. Some controllers tie phase amp output to battery amp input by some 2 to 2.5x multiplication ratio.)
Going from a generic KT 22A controller to a 35A KT will give over +50% torque. Up till the motor hits magnetic saturation, torque scales linearly with the amps. The thinnest kind of direct drive (27mm magnets) can hit 80-90nm too. Most of those are 30mm nowadays and can push 100nm tho.
On the geared hub motor side, the G062 (most 750w bikes use clones of it) can push 90nm before there's a risk of stripping nylon gears. Smaller ones like the G310 may strip gears earlier. These generally need less amps to produce torque than direct drive, so they work better with poor electrical systems.
Worth mentioning that wheel size matters for torque on hub motors. Larger wheels need more torque to climb (thrust). And also motor wattage doesn't mean much for torque (phase amps from the controller and gearing affect that even on bikes sold with the same wattage rating).
I also find the throttle gatekeeping or wattage gatekeeping a bit silly. Going 25kmh by throttle or peddling has no difference in how dangerous a cyclist is on the road. They should cap top speed and acceleration on throttles, but banning them outright unless someone is doing a minimum cycling motion on the pedals is a wrong regulatory approach and limits accessibility.
Throttles above 6kmh (walk assist) are banned across the whole of Europe. Judging by how heavily the Netherlands pushed for the EU-wide throttle ban, and putting my tin foil hat on, I can assume this was done as regulatory capture to ban Chinese ebikes from local stores, as they come with throttles and aren't usually capped at 25kmh on pedal assist. Netherlands produced ebikes are all pedal assist only, mid-drive, and have very poor batteries and electrical stuff for the (over 2x) price they're sold for. And now they have less competition. EU also has a 45% tariff on "e-bike part" imports...
I would also like a regulatory framework to register and insure a faster e-bike (as imo they should not cap wattage and cripple the hill climbing torque, only speed/acceleration) for adults. Right now you can only register one that has a license in EU. If you build your own, it can never be legal, even if you have a motorcycle license and want to insure it. This class of e-bike is impossible to drive legally right now.
L1-b class registration can technically do this, but it needs the bike to be registered in Europe. No e-bike has this. No manufacturers sell class L1-b e-bikes registered in the EU. Only some electric motorcycles afaik.
Doesn't it help changing gears? You can even get sprockets changed to lower the gearing for more torque.
Depends on the bike. On some bikes the motor is mounted in the rear wheel, in which case there's no gear between the motor and the wheel. On other bikes the motor is mounted between the pedals and sent to the rear via the chain, in which case shifting works as you expect. But the latter style (a.k.a. mid-drive) demands custom frames (because mid-drive motors are nonstandardized), which increases costs and decreases repairability. In contrast, rear-wheel motors can fit on literally any frame, so they're much more accessible.
> But the latter style (a.k.a. mid-drive) demands custom frames (because mid-drive motors are nonstandardized),
This is somewhat overstated. Bafang middrive conversions fit on most frames with a BSA bottom bracket.