Why are two speed transmissions not more prevalent?

Full disclosure: I'm a mechanical engineer /hobbyist motorcycyle builder starting to design a bike from the ground up as a long term project. I have searched through the forum for subjects related to transmissions, but other than a few dead ends, it doesn't seem to be a widely discussed topic.

We have motors capable of providing impressive power in a relatively small package. All small/medium e-motorcycles I've come across tout impressive acceleration but lack the top end/cruising ability of equivalent IC motorcycles.

With the power available, why is there no widely available two speed gearboxes on the market that could both improve low end acceleration and top end speed /efficiency?
A small, high torque gearbox shouldn't be too hard to put together, or be particularly heavy if well designed. The attached sketch is one example that should work, the only downside I can see is that regenerative breaking wouldn't work in the first gear due to the sprag clutch, but that could be overcome by automatically engaging the second gear under deceleration. A clever control circuit could also rev-match the motor input to the second gear speed to help with engagement.

So I guess my question is: why aren't transmissions more widely used in e-motorcycles, am I missing something?






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ES veteran Thud built a tiny 2-speed for racing a bicycle. Derailleurs and cassettes were not strong enough for his application.

https://endless-sphere.com/forums/viewtopic.php?f=28&t=8644&start=150#p195730

The Porsche Taycan uses a 2-speed on the rear, one-speed on the front.

Tacita, Brammo, Horwin, and others use a multi speed transmission on their electric motorcycles..

I'm also very curious about the use of a gearbox but in my mind it makes more sense to just use a larger motor if more top speed is required, that way it is simpler/less to go wrong, less losses from the gearbox and potentially less weight.

but would love to hear pros and cons to both set ups

some threads in these lists are discussions of parts of this topic
https://endless-sphere.com/forums/search.php?keywords=gearbox*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search


https://endless-sphere.com/forums/search.php?keywords=transmiss*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

One reason is that you can size your motor/controller/battery to the peak load and then run them at partial load without a significant efficiency hit.

Controllers and batteries are advanced enough now that transmissions aren't part of the path forward.

I don't need it because I use a three-button switch, with 3 different powers and speeds, I start with the delicate only to prevent gear breakage,
it's enough for me, and it regulates my pas according to the law, (separately from the throttle).
consuming a few extra watts doesn't bother me with a substantial battery.

Hauling hundreds of pounds up long steep climbs at low speeds off road

vs road speeds on the flat

with the same bike can't be done without gearing.

Powerful & sophisticated electronics might make 2-3 gears enough, but not eliminate them entirely

Two things:

1) Electric torque curve gives max torque from standstill
2) Extreme electric power density

This tends toward a situation where in weight and cost terms you are better off slightly oversizing the motor than adding a transmission.

Come on don't tell me you didn't think of that before posting the thread.

I would like to add a few thoughts. If you are designing an electric scooter/motorcycle from scratch to sell to the public...I agree that the best configuration is to use higher watts that are feeding a larger motor in a "one speed" system. That being said...

If you are converting a gasoline-motorcycle to electric, there is a definitely viable option to use the existing transmission and output sprocket.

Again, that being said...most existing motorcycles have a 5-speed/6-speed transmission. The fairly flat torque-curve of an electric drive-train means that most E-conversions end up using only two or three gears.

https://www.electricbike.com/rich-benoit-converts-an-old-skool-rat-rod-to-electric/

flat tire said:

1) Electric torque curve gives max torque from standstill
2) Extreme electric power density

This tends toward a situation where in weight and cost terms you are better off slightly oversizing the motor than adding a transmission.

Click to expand...

1) all motors..inc electric, have a limited RPM range
2) all motors have reduced torque, power, and efficiency, at the extremes of their rpm range.
Intelligent selection of one or more gear ranges can optimise performance and efficiency.

The weight / cost comparisons is highly debatable between an extra gear ratio, and a bigger motor, controller, battery , combination

Hillhater said:

1) all motors..inc electric, have a limited RPM range

Click to expand...

True - but so do bike wheels.

2) all motors have reduced torque, power, and efficiency, at the extremes of their rpm range.

Click to expand...

Most DC motors have MORE torque at low RPM. And at higher RPM's, most DC motors can handle more power. Which is a good match to a bike, which might need very high torque at low RPM, and then high power at higher speeds to overcome air resistance.

That being said, I agree there are cases where a transmission might get you a lighter solution for a given desired power.

I’ve tried to draw some two speed gearbox designs. They’re certainly a good idea if you have access to machines and skill.

There are several issues that stop most of the diy gearboxes from being viable.

Tight tolerances needed
Hardened gearsets cost big bucks and you can’t live without them due to many reasons
specing for durability drives complexity, cost and weight

Overspecing motor and battery is much easier and in most cases the right choice as it often easily matches the gearbox system in both cost and weight

Buuut i’d like to see you prove us all wrong with your own design.

This topic has been gone over quite a bit here. https://endless-sphere.com/forums/viewtopic.php?f=30&t=47930&sid=90b034ac92e3f9a1eb17ebdfac3b1f11

I had to come to my own conclusions after much thought and learning on the topic. Most of what I learned is that if your constrained to using the lower cost standard ebike components, you could end up with some benefit. However if money is no object, you would always be better off adding the same amount of weight in the motor and eliminate the added complexity and failure points.