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Let's see how far the trend of motorcycle-disguised-as-bicycle is at. Electric drive is penetrating most market segments. The front derailleur is dead.

I believe all types of electric motors have an optimal operating point (torque-speed) BUT are "rather efficient" is a large region around it. Could we do away with the massive gearbox and old-timer RD? The lack of gearing will be of little concern if the intended use is akin to the nowadays popular electric scooters - ride, never pedal. And battery capacities are only going to improve.

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    Since singlespeed electric bikes exist, I'm writing this as comment. The main appeal of single speed is simplicity, robustness, low price and preferring skill and strength over technology. Electric assist doesn't really fit together with any of these. Also, at least in EU law requires electric bikes to be pedaled with electric assist and while it is not really enforced, selling "electric assist" bikes that are clearly intended to not be pedaled could get the seller in trouble.
    – ojs
    Jul 16, 2022 at 13:40
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    Keep in mind that in most parts of the world, if you don’t have to pedal it to make it move, it is an electric motorcycle, not an e-bike. This really limits the possible market for such a design. That said, an IGH does just as good of a job of getting rid of the RD, and I’ve actually seen some very well designed e-bikes using Rohloff Speedhubs (and, for that matter, some with electric autoshifting using Fallbrook NuVinci hubs as well). Jul 16, 2022 at 19:59
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    I would like to disagree with the notion that the front derailleur is dead, but it’s not important for this question. 1× is just not great for road riding.
    – MaplePanda
    Jul 16, 2022 at 21:26
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    @ojs As a fit enthusiastic rider the idea is an abomination to me. However I could see the attraction to someone that just wanted to commute to work or go see some scenery without actually requiring physical exertion. Lets say you only wanted to push 50W of power at 60rpm no matter up/down/flat. Well in that case a motor can pick up the slack and keep you travelling at 25km/h on all but steep climbs = the simplicity of a single speed makes sense. If you barely want to pedal you probably don't want to shift gears either
    – Andy P
    Jul 16, 2022 at 21:51
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    "FD is dead" ?? as a fattie who climbs like a brick, you can prise my triple from my cold dead fingers.
    – Criggie
    Jul 16, 2022 at 23:22

4 Answers 4

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Electric Bike Report has written an article on this topic. They mention 3 different models.

  • Rad Power Bikes RadMission 1
  • KBO Hurricane
  • Volt London

On top of this article, I would also add one of the most funded ebike start-ups (Cowboy), that uses a single speed design with variable assist since their first model.

On the top end segment of more traditional (utility) manufacturers: Riese&Muller also released one recently, but they also offer IGH and derailleur versions along.

It looks that this solution is well-suited for urban riding, with low top speeds ...exactly like muscular single speed bikes in fact.

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    As an aside, I had a Radmission in recently with a dead freewheel. The one that comes on it is a DNP, which I've seen fail quite bit over the years and have a low opinion of, even though they're not really all that cheap. I tried replacing it with a Shimano MX30 that I had on hand, and it didn't fit because the motor hub was so long it ran into the tool fittings, a problem I was oblivious to the possibility of until that moment. (Usually that wouldn't even happen with the same freewheel going on a multi-speed FW hub). So that bike appears locked in to using only certain, crappy freewheels. Jul 16, 2022 at 18:51
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They do not make the majority but they do exist, see here for instance for a modern model with disk brakes and belt drive. It is, indeed, somewhat lighter and somewhat cheaper while the rather small 252 Wh battery also contributes to this. It would need daily charging for my commuting.

It has the gear ratio of 2.5 (50:20) that looks well thought. That would be close to my 18 teeth sprocket (38:18) that would comfortably take most of the hills in the surroundings but riding at higher speeds may be annoying if you do not like cadences much above 60, once per second.

I mostly use the 12 teeth sprocket (38:12 ratio) that works well on moderate hills at 21 km/h with assist from the engine. I could probably use it alone for all my commuting that is rather flat but there are hills nearby that benefit from slower gearing, and for cruising at 25 km/h the smallest 10 teeth sprocket is much more convenient. Hence at least 3 gears are probably still closer to optimal, even with the good today technology. My usual cadence that is seen in the bicycle computer is about 50 to 55.

3

Yes, single-speed electric bikes exist, and they have at least one important market niche which they're particularly well suited for: urban pay-as-you-go rental bikes.

These bikes are basically competing directly with electric scooters for (almost) the same market, so they have very similar design considerations. And one of the most important drivers in this market is simplicity: you want the bike to be as simple and easy to use as possible, so that a new customer can just hop on and ride it easily, and you also want it to have as few breakable parts as possible. Eliminating the gear shift serves both goals well. And in this market niche the loss of features like the ability to pedal faster than the electric assist limit on flat ground is of little concern — the bikes are still faster than the scooters they're competing with.

For one example, Freebike — a company that recently started operating such bikes where I live — has no user-selectable gears on their e-bikes. (AIUI from a bit of googling, the bikes do have some rather advanced gearing built in, but it all operates automatically.) In my experience, the bikes also have the e-assist configured rather aggressively, to the point where you can indeed pretty much just make a token effort of spinning the pedals and the motor will do all the hard work. (It is possible to out-pedal the motor, but that's clearly not intended to be the primary mode of operation for them.) Looking at their website, they apparently also have non-electric bikes that (presumably) do have gears, but I can't comment on those models as they're not available here. (There's already a rather extensive municipal network of non-electric rental bikes here, so they probably decided not to even try to compete with those.)

1

Let's see how far the trend of motorcycle-disguised-as-bicycle is at

There used to be a motorcycle-disguised-as-bicycle. It was called the moped. It had a MOtor and PEDals. However, the motor was an internal combustion engine that worked well at high speeds when making lots of power and was very inefficient at low power, whereas cyclists produce low power at low speeds. It didn't combine the best properties of motorcycles and bicycles, instead it combined their worst properties. Soon the pedals were ditched but the motor stayed, and today moped means a motorcycle limited to low speeds.

However, electric bikes are different. Electric motors can be made to operate at low powers, so low that they are generally only assisting the rider and not being the primary propulsion method. Actually at lower power levels, the energy efficiency is better. The speed mismatch of electric motors and pedaling cyclist was solved by making the motor mid-drive, where a high-speed motor is turning the cranks at low speed by a single-speed gearbox internal to the mid-drive unit.

The 25 km/h limit (if going over that speed, assist power becomes zero), combines very well the best properties of cyclist and battery. If going on flatland, good bikes with low rolling resistance tires generally attain speed above that so on flatland riding, no energy from battery is consumed. On the other hand, if speed drops even slightly below 25 km/h such as on an uphill, the motor assists fiercely at nearly 500 watts1. I can have very high speeds uphill, far higher than athletic road cyclists attain, while at the same time allowing a 500 watt-hour battery to last 150 km. At an average speed of 20 km/h, that's only 67 watts of average assist, but has the uphill performance of nearly 500 watts. A moped where the motor assist only uphill would be ridiculous, as the internal combustion engine would be wasting lots of fuel when not going uphill. I can assure you that not a single internal combustion engine can have 67 watts of average energy usage, as that would be only 7 milliliters of gasoline per hour. Even a small unloaded engine would idle with 250 milliliters of fuel used per hour.

I believe all types of electric motors have an optimal operating point (torque-speed) BUT are "rather efficient" is a large region around it. Could we do away with the massive gearbox and old-timer RD?

No. If the primary propulsion method is motor, pedals are ditched and the motor is sized such that it can produce lots of power even at low speeds (when traveling up a steep hill) but also produce the same power at high speeds (when driving on flatland), then we could have no gearing, like we do with electric cars. Then we would end up with electric bikes where we ended up with mopeds, i.e. they would be motorcycles. However, you have to remember that current electric bikes are electric bikes, not motorcycles-disguised-as-bicycles. The primary propulsion is still pedals, and to make that primary propulsion work well, gearing is needed.

It's true that electric bikes go faster up hills, so less of gearing is needed. But there is still need for gearing. I generally use about half the gearing range on an e-bike than the one I would use on a normal bike.

And battery capacities are only going to improve.

False. Weight is the limiter. There is only very slight possibility for optimizing capacity per weight. Lithium ion batteries are already very close to their theoretical limits.

(1): If somebody notices that electric bikes are only allowed to assist with 250 watts, that's not the max power, that's the average power over a long interval. As I showed with the battery life, in my usage the average power is 67 watts, far below 250 watts.

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    Interesting wattage numbers. I’m interested in sources for them.
    – ojs
    Jul 16, 2022 at 16:34
  • 500 watts = 70 newton-meters at 70 RPM or an angular frequency of 7.33 radians per second (for example latest Shimano motors produce way above 70 newton-meters actually so that 500 watts is for an older motor). 67 watts = 500 watt-hour battery lasting for 150 kilometers at 20 km/h.
    – juhist
    Jul 16, 2022 at 17:20
  • So, you made up the number? It explains the answer.
    – ojs
    Jul 16, 2022 at 21:04
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    Interesting - I always thought mopeds came about because they allowed the use of a much smaller liquid fuel motor by using the pedals to get up to speed and negating the need for a clutch and gearbox.
    – Criggie
    Jul 17, 2022 at 4:54
  • @ojs According to your definition of "made up", if I purchase two 60 ampere hour batteries (as claimed by manufacturer), and claim the capacity is 2 * 60 Ah = 120 Ah, the 120 Ah figure would apparently be "made up", right? Or If I measure that the 60 ampere hour battery actually has 59 Ah capacity, then my total capacity 2 * 59 Ah = 118 Ah would be "made up", right?
    – juhist
    Jul 17, 2022 at 10:27

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