eBikes: How do I conceptualize Pedal Assist so I can find what I need?

May 15, 2023 12:59 PM

I rented two eBikes this week. The first one was the Giant Roam E+, and the second was the GEN3 Stride. They both had pedal assist, but the experiences were completely different from each other. I want to understand how best to think and talk about what I felt while riding each, so that I can buy an eBike that feels right to my style of riding.

I'm used to riding a drop bar road bike throughout the city and beyond, and sometimes find it useful to rent an eBike to scout out a new route to plan for future rides, so I can ride the route faster than usual and cover ground in more time without getting as exhausted. So, if I normally average 11mph with my regular bike, I want to average maybe 15-16mph on an eBike.

The Giant Roam E+ had I think, a 7 speed cassette, and when I pedaled with various levels of assist enabled, I was able to feel a comfortable level of resistance, like the bike was letting me do as much work as I wanted to, and the motor was happy to step in politely to boost me 3-4 mph when I needed it. This felt like a natural way for me to ride.

The GEN3 Stride also had a 7 speed cassette, but even in the highest gear, I couldn't feel any resistance when the pedal assist was enabled beyond level 1. It felt completely unnatural, and ghost pedaling just to reach 12-15mph seemed hugely inefficient. It's like the bike wouldn't even let me get a workout unless I turned the pedal assist completely off, then I was riding a 50lb bike at 8mph.

Is there a more industry standard way to talk about this integration (or mismatch) between the gearing of the bike, the resistance the rider feels, and the pedal assist assertiveness?

Which of my experiences is more typical of pedal assist eBikes? Before I go out and test ride even more bikes, is there some language that would help me to weed out all those bikes that disdain my pitiful attempts to try to help the motor?

posted by oxisos to Health & Fitness (7 answers total)

Best answer: The Roam E+ likely had a torque sensor on it, which is a more expensive system that gauges the effort that you are applying in order to augment that effort with e-assist.

The Stride likely had a cadence sensor on it, which is a simpler and more inexpensive system that bases its level of e-assist on the fact of your pedaling and the speed at which you are driving the crank.

From everything I have read, a torque sensor system is the most natural-feeling to a rider of "acoustic" bikes but due to economics, I think cadence sensors are more common.
posted by gauche at 1:09 PM on May 15, 2023 [8 favorites]

The cadence sensor thing is a good thought, although my RadCity has a cadence sensor and it feels fairly intuitive except when I get up to the max motor speed (20mph). I suspect there is variation in the way cadence sensors for different brands/bikes work and the way the computer interprets the inputs from the cadence sensor.

Also do you know whether the cassettes were different? I wore out the cassette on my ebike in the first 1000 miles, partly because I was always in the top gear. The bike shop replaced it with a differently-geared (but still 7-speed) cassette, so that I'm not in the top gear quite as often.

This is a big generalization but I think that bikes that are marketed as road or mountain bikes are more likely to prioritize natural bike feel while bikes marketed as city or cargo bikes are more likely to prioritize "just let the motor get me there."
posted by mskyle at 1:17 PM on May 15, 2023 [2 favorites]

Best answer: I agree it's likely mostly down to torque vs cadence sensor - and how good the manufacturers are at tuning output power to those inputs. When I was last shopping, I came to the conclusion that Bosch was best at this (but sure knows how to charge for it). That was a couple years ago though and I didn't do exhaustive research. I'm sure there are lots of good alternatives.

Also worth pointing out the other big difference between those bikes: the Giant has a mid-drive motor (between the pedals, affected by gearing) and the GEN3 has a hub motor (in the wheel, not affected by gearing). Not sure how much that affects the problems you noticed but in general I've found mid-drive to feel more like a regular bike that just happens to be easier to pedal.
posted by davidest at 1:30 PM on May 15, 2023 [3 favorites]

Best answer: Gauche and davidest have it. The biggest difference is between hub-drive and mid-drive. Hub drives usually have a cadence sensor, and mid-drives usually have a torque sensor. Cadence sensors can feel "lurchy" as they can kick in a little late, and depending on the assist level, spin up to max-assist as soon as it's activated.

Part of the reason mountain bikes prefer mid-drive engines is they're built for climbing - with a mid drive engine, your engine's power goes through the gearing and drivetrain, so you can use the full strength of the engine to drive the smallest gear, and get amazing climbing performance. Hub drives just turn the wheel directly, and may have some internal gearing, but either way are not able to use the bike gears.

A sort of confounding factor is that mid-drives are much more expensive, and I think R&D in the controller software and more care and attention taken with the programming of things like easing on the assist vs just switching the assist on full blast accounts for some of the difference in feel. I've read reports of people customizing their controller software for hub-drive bikes and getting very natural feeling results, so it's not purely the technology that is causing it.
posted by Jon Mitchell at 1:31 PM on May 15, 2023 [2 favorites]

Best answer: Gauche is correct.
Bikes with only cadence sensors tend to have an 'all or nothing' response, since the bike has no idea of how much power/force you are applying to the pedals; if the pedals turn you get the power set by the chosen boost level., all at once.
Torque sensors will provide a boost proportional to the power you exert up to the chosen boost level, so they have a much smoother & more natural response curve.
I have a Giant and it has both sensors. feels mostly like my 'analog' bike.

on preview, ditto with others.....
posted by TDIpod at 1:37 PM on May 15, 2023

I have a Bosch mid-drive ebike - that seems to be the most common motor type here (for higher-end bikes, at least). It has the torque sensor as described above.
posted by EndsOfInvention at 3:18 PM on May 15, 2023

Best answer: Aside from hub motors vs mid-drive motors, there's also Class 1/2/3 e-bikes. Class 1 are pedal assist up to 16 mph; Class 2 can be run purely on electric power up to 20 mph; Class 3 are pedal assist up to 28 mph. These are regulatory categories, but you can also just look at e-bikes and see a philosophical categorization into "bikes, but with power assist," and "mopeds, but with electricity." The former look like bikes, and are often electrified models of acoustic bikes. The latter don't put you in an efficient pedaling position since you're not really expected to need to pedal much—this includes some "assist" bikes where the assist is doing the lion's share of the work. With some e-bikes, you can set the degree of assist.

Also, fwiw, I get the impression that a lot of the moped-style e-bikes are underbuilt, because they're designed to hit a price point, and I worry about their safety. But the nice bike-style e-bikes can be crazy expensive.
posted by adamrice at 6:34 PM on May 15, 2023