Why is it rare for an e-bike to have more than one chain-ring?

[QAJAQR]

Because you don't need so many gears when you have electric assist? (And has anyone ever thought that they could use a wider range of gears or smaller steps between gears on their e-bike?)

Because another chain ring gets in the way more on an e-bike than an acoustic bike?

Other stuff I haven't thought of?

 

[smorgasbord]

First, there's an impact on the Q-factor. Larger Q-Factors move the pedals further away from each other, which hurts efficiency on comfort. More rings increase the distance between the pedals.

Now there are 12-speed rear cassettes with 500% or more range, so there's less need for more than one chainring up front, especially since you've got a motor. And with that motor you don't need such small steps between each gear.

Also, cross-chaining on an e-bike could be disastrous. This is using the big sprocket up front with the big sprocket out back, or small up front with small out back. The angle the chain has to ride means the chain doesn't sit well on the cogs/chainring and can wear them out very quickly - not to mention chain tension/slack issues.

Finally, e-bikes are complex enough that anything to simplify things is good.

 

[Ken M]

The more assist you have from the motor the fewer gears that are needed to optimize the human power input.

In reality I think an optimized ebike could get by fine as a fixie but cadence becomes an issue if you want a rider to really be able to keep up at speeds say over 25mph. Riders are actually pretty good at applying a lot of torque at start to slow speeds where motors are less efficient but people perceive an ebikes acceleration as the best example of performance while I tend to think the best metric is how effective the motor and rider are at sustaining speeds from say 15-35mph (I know I'm going to get hammered by those that feel motor assist should never go that high but those people are just riding around the neighborhoods and not worried about shaving time off their serious commutes (in other words, their opinions are biased because even if they were walking it's not a problem time wise).

 

[Ken M]

The new rear cassettes provide 500% or more gear ratio range which is amazing and good enough for most mtn bikers.

I just think a really good ebike could be designed as a fixie and be a great urban commuter for most cities (most cities are not that hilly and for those that are it would make sense to go with an IGH with 3 to however many gears are needed for the terrain you are faced with typically - San Francisco for example probably pushes even ebikes to max out on gear ratios).

 

[QAJAQR]

Thanks for all the responses.

For me, the most interesting point was one I hadn't thought of, but should have: potentially disastrous consequences of cross-chaining. Even without the help of electrical horses, cross-chaining can damage the drive train on an acoustic bike.

Thanks, Smorgasbord

 

[TomD]

Some mid drive motors aren't compatible with more than one chain ring as well. Probably more a consequence of not being necessary than being a reason why.

 

[steve marino]

My eBike has 21 speeds, with three on the crank. I'll soon be replacing the drive train on it and going to a single sprocket because I have never used anything but the largest one.

 

[ruffruff]

Not sure this is an Ebike thing. Most mnt bikes today don't have a front derailleur.

 

[indianajo]

I have 24 speeds on my bike left with triple front sprocket, and use them all when I bike powered by me. 32:32 will get me & 80 lb groceries up a 15% grade @ 1 mph, 52:11 will allow me to help the motor at 23 mph.
Since it is hubmotor bike, first chain lasted 5000 miles. 8 speed chain outlasts 9 10 11 or 12 speed chain because it is wider. I ride pedal powered for heart/lung health, unless wind is >12 mph in my face, or trip is over 25 miles. I don'tunderstand post 2 about "cross chaining", and my waist is 32" so if anybody should have trouble clearing 3 rings it should be me. I don't. Currently shifting the rear is causing major pain in my r. thumb joint, so I don't, I shift the front only. 3 speeds, 32:24, 42:24, 52:24.
Only 1 mid-drive motor allows more than 1 front chainring I am aware of, Yamaha. And most don't have it, it costs. Nobody but me buys an electric bike to pedal it himself. I view motor as a 12 lb gadget that eliminates 6 hour 144 bpm hot days like in September 2018. 3.5 hour trips of 30 miles whatever the weather is doing.

 

[harryS]

I have front derauileurs on three ebikes with hub motors. One would think them redundant, but it allows a better cadence choice for changing elevations and wind with a cadence sensor, if you're riding on pedal assist at slower speeds.

If you're bombing along at max assist, or have torque sensing, you probably don't care.

 

[fooferdoggie]

I have front derauileurs on three ebikes with hub motors. One would think them redundant, but it allows a better cadence choice for changing elevations and wind with a cadence sensor, if you're riding on pedal assist at slower speeds.

If you're bombing along at max assist, or have torque sensing, you probably don't care.

Yes when I test road e bikes I could not find the right gear to keep my 80 rpm vacancy. I just kept going faster. but you never see any commercial hub drive bike with multiple chain rings. you see higher end road bikes with them.

 

[Browneye]

Yamaha offered some double front chain rings on their bikes, so you'll see some haibikes as well with them.
Not really necessary for a ebike.

I did a hub conversion on a Roll and it was a 21spd - going to 7 was just a non-issue with the drive motor. And it really cleaned up the crank area as well as the left bar - the throttle went there instead of the shifter.

It's way faster with the motor than it ever was pedaling it. LOL

 

[Stefan Mikes]

Let us clarify one thing:

1. Mid-drive motor e-bikes are typically equipped with a single chain-ring (exceptions exist as Browneye has said);
2. Hub-drive motor e-bikes are often equipped with multiple chain-rings.

With the geared hub motor (in most instances), the motor provides constant assistance to which the rider must match their cadence. Such e-bikes are typically poor climbers unless very powerful motor is used. In case of steep climbs, the rider has to downshift dramatically to help the motor with leg power. Hence, multiple chain-rings there.

The mid-drive motor acts together with the rider's leg power through the drive-train. The motor + human input at the cranks is amplified at the rear wheel. Therefore, there is no need for multiple chain-rings there, especially as modern 1x drive-trains have a large gearing ratio range. Many people riding on the flats even complain they have too many gears.

Yet another fact is the cranks of the mid-drive e-bike are mechanically separated from the chain-ring. When you pedal, you don't drive the chain-ring with your legs spinning; you spin the drive shaft. That movement is combined inside the motor with the motor power and the combined power is transmitted to the chain-ring (that's why spinning the cranks backwards takes no effect on the chain-ring). Then, there is a torque sensor at the crank-set side. Adding more chain-rings would make the matters excessively complicated. So, 1x chain-rings are supported by most of mid-drive motors.

A hub-drive motor e-bike is mechanically a traditional bike with the motor added. The mid-drive motor e-bike is an e-bike from the very beginning and design rules parameters are different.

 

[Browneye]

>snip

A hub-drive motor e-bike is mechanically a traditional bike with the motor added. The mid-drive motor e-bike is an e-bike from the very beginning and design rules parameters are different.

This.

 

[Deleted member 4210]

Multiple front Chain Rings come standard on 3 models of Yamaha ebikes (mid-drive), couple models of Magnum ebikes, and couple models of NCM ebikes. There are probably more but that's just a few of the brands and models I have in my shop.

P.s. personally I think they are a pain in the you know what. From my perspective, the question I would ask is why on earth would you want to put multiple front chain rings on ANY ebike ? With the extra power from e assist, an Ebike OEM could design it with a larger front chain ring, and do 11 or 12 speeds on the rear hub. I'd prefer the simplicity of a design like that over multiple chain rings any day.

 

[Stefan Mikes]

Multiple front Chain Rings come standard on 3 models of Yamaha ebikes (mid-drive)

Agree. Their users believe that's an overkill

 

[PDoz]

My 2018 full e pro at about 35 km - I changed up on the front cog at about 15 kph , from memory I was in mid assistance at the time (250% boost) . Yamaha pwx , shimano xt shifter but praxis crappy sprockets.

The lbs negotiated a replacement with a single race face 34 tooth and it's been fantastic

 

[PDoz]

A closer picture - I'll never know if this was caused by a faulty sprocket, my own stupidity, or simply dual front chainrings are a BAD idea. I'll also never really know if my premature / rare yamaha pwx failure was due to damage caused when everything locked up - the torque sensors started playing up around 2000 km and that motor was always a LOT more sloppy / noisy than the 2020 version giant replaced it with

 

[Deleted member 4210]

From my perspective, the question I would ask is why on earth would you want to put multiple front chain rings on ANY ebike ? With the extra power from e assist, an Ebike OEM could design it with a larger front chain ring, and do 11 or 12 speeds on the rear hub. I'd prefer the simplicity of a design like that over multiple chain rings any day.

Or give me a 48 volt mid drive, 500 watts from Yamaha (they dont make that yet) with a Gates belt, and 14 speed Rohloff rear hub. And if Yamaha added a throttle to their mid drive, I'd buy it in a heartbeat. And You probably would not have to work too hard with a combination like that to reach 35 mph.

 

[Stefan Mikes]

and 14 speed Rohloff rear hub.

Rohloff gets bad reviews recently.