E-Bikes: Cadence-Sensing Motors vs. Torque-Sensing Motors

E-Bikes: Cadence-Sensing Motors vs. Torque-Sensing Motors

I stumbled upon a really interesting Reddit thread some days ago that happened to be on a topic I’d been recently considering in some depth. Tl;dr: the writer switched from a cadence-sensing motor to a torque-sensing motor and now feels like they’re using a lot more energy to accomplish the same commute.

This comes only a handful of days after riding one of Cannondale’s latest-and-greatest e-gravel bikes with a torque-sensing Bosch motor system built in. It was at that point that I realized all of this: cadence-sensing motor systems are for when the point of the ride isn’t the ride. Torque-sensing motor systems are for when the point of the ride is. Let me explain

Cadence based hub motors are pretty simple. Once you start moving, the motor within the hub kicks in and works to get you up to some determined speed (typically this is split into levels: PAS#1 = 10mph, PAS#2 = 13mph, etc.). Along the way the motor might get the wheel spinning faster than your feet are spinning the cranks and chain. Now you’ve entered the “ghost pedaling” zone — you’re pedaling, but it’s not connected to (or contributing to) the propulsion of the bicycle. You are a ghost in the motor’s world! This is an easy fix for hub motors. Shift up. And keep shifting up until you feel that you’re connected to the drivetrain again. At that point you have the best of both worlds: you’re mechanically connected to your drivetrain and spinning with it, but the motor is actually doing most (or all) of the work. As you spin, you can continuously choose to flex your thighs more or less and the hub-motor will compensate in kind. If you want to spin with the drivetrain but not actually put any ‘oomph’ into your pedals, that’s fine! You’re not ghost pedaling, but the motor is doing all of the actual effort (someone has to! 😜). Conversely, if you do want to put ‘oomph’ into your pedals, the motor will ease off proportionally — now you’re essentially splitting the effort required to keep your bike going at this speed.

But the idea critical to the Reddit writer’s point here is that with a cadence-sensing system, you can operate the bike in a state of ‘the motor is doing all the work’ even though you’re still pedaling with the system.

(Cadence-sensing mid-drive motors can accomplish this too, but it’s more difficult to tune just right. I cracked that sauce for the BBSHD, but most mid-drive systems aren’t configurable this way. Luckily, most OEM mid drive systems are torque-based, so this isn’t an issue for most folks.)

All of this contrasts with torque-sensing motors. The idea that you can be mechanically connected to your drivetrain riding ‘with’ the motor but the motor is doing all the work… just fundamentally isn’t how torque-sensing works. Torque-sensing will always be a multiplier of your input torque. You will always have to be putting torque into the system for it to multiply. “Eco” may be multiplied by 1.5x (adds half the watts your foot is putting out), “Tour” may be 2x (what you put in, the motor does too), “Turbo” may be 3 or 4x etc.. but that still requires you to provide a level of input torque yourself. Especially if you want to maintain high speeds. Even if you’re on a flat, trying to maintain 25mph on a typical bike/rider setup is probably 200-300 watts continuous. If you’re on a 4x “Turbo” setting, that means you still have to continuously output 75 watts yourself (the motor does the other 225). Which ain’t nothing! When you hit a hill you might need 600-700 watts to get up that hill with moderate speed. Again, on a 4x “Turbo” mode, that’s 150-175 watts of output from you! Which is definitely something!

Anyway, all that to say, I realized a couple of weeks ago that for riding styles where the point of the ride is the ride (bike touring, cycling workouts, etc.. anything where you’re doing cycling as a sport), torque-sensing motors are for sure the better option. They’re more intuitive, they keep you involved in the drive-train all the time, you cannot ghost pedal or throttle your way to glory — all good things for that type of riding. They’re great! I would totally ride one on a road bike with all my spandex. But for riding where the point of the ride is not the ride, but rather that you’re just using the vehicle to get somewhere (commuting, cargo bikes with kids, getting groceries, etc.), cadence-sensing (when setup correctly!) just is the better option (IMO).

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