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[Low On Cash]

Advantages of Multi Speed Transmissions for Electric Motorcycles - Mike Mas

Hey guys - thought it would be a good topic to discuss the advantages of a using a 2-3 speed gearbox for or electric motorcycles. Its a proven fact that multi-speed transmissions offer an advantage of both range and performance.

Not too be misinterpreted - I’m perfectly happy with my single speed DSR Zero and understand the complexities and weight of using gear box. With that said - if Zero or any manufacture offered a new technology motorcycle with a 2-3 speed gearbox, I would be the first to get in line to buy one.

There are major advantages regarding performance and range when using a multi-speed gear box on electric cars, motorcycles and bicycles. Test have shown there is a 10-15% reduction in battery usage when using a 3 speed gear box in comparison to a single speed transmission.

While not applicable to motorcycles - there is new transmission technology called; MSYS, its a three speed transmission designed for electric cars to handle the torque of modern electric motors. The MSYS transmission uses “Cone Clutches” which offer many advantages over wet type multi clutches. These gear boxes are shown to operate at torque levels of up to 1500 ft. lbs. of torque, well above even Tesla’s powerful requirements.






As I previously mentioned, While Tesla uses a ZF single speed gear box, they realized there would be range and speed advantages of having a multi speed transmissions and spent time and money in an attempt to build one, however the project failed because of difficulties in manufacturing a transmission that could withstand the torque of their motor(s).

Typical Telsa Drive System



A company that was successful with multi-speed drives is BWM. On their BMW i8, Electric / Gas powered sports car, they drive the front wheels using a propriety motor and a GKN two-speed automatic gearbox. This transmission remains in the lower gear (11 to 1 ratio) while in “Electric Only” mode. Once the Turbo engine is started it then switches to second a higher gear (6 to 1 ratio). The two speed gear box allows exceptional “off the line” performance and improved high speed performance up to 155 mph.

BMW I8 Front Electric Drive w/ 2 Speed Transmission



Back when Tesla was trying to develop a 2 speed gearbox, I always wondered why they just didn’t compromise and use two different ratios on their 4 wheel drive cars. The front could be a lower ratio and the rear would be a higher ratio. Since they operate on separate motors there would be no syncing of the front and rear sets. A processor would make them work in unison on acceleration then supply more or less power according to speeds. Off the line, the lower ratio would provide more work, then at higher speeds the low ratio front drive could be at idle or low power while the high ratio rear would provide the majority of power to propel the car.  If BMW could sync an electric front drive and a turbo gas powered drive - then it would be a no brainer to make the multi ratio drive successful. 

BMW I8 Chassis




Its difficult to understand the advantages of a gear box with electric unless you have the opportunity to feel it for yourself. I say this because for close to 20 years I have been building and riding electric powered bicycles. With an electric powered pedal bike you have the distinct advantage to “Physically” feel the advantages when using a gear powered electric bike, verses a single speed.

The best way to describe this difference is to compare a “Hub Motor” bike system to a “Mid Drive” system. I’m sure some of the users of this forum have experience on electric bikes and will confirm the differences of a single speed drum motor verses a center drive.

Outlaw 1200 watt Hub Motor



The Hub motor - Is mounted in either the front wheel or rear wheel or in some cases both wheels and somewhat like our Zero uses a fixed, single speed ratio. Hub motors are offered in two configurations which are both single fixed ratios. The more common hub motor has fixed magnets mounted to the outer shell of the hub motor. Another hub design uses a planetary gear system to reduce the ratio to allow the motor to spin faster for more starting torque, however both of these system are single speed fixed ratio systems.

Bafang 1000 Watt Center Drive System



The Center Drive system - This application allows the motor with a reduction gear to mount on the pedal tube with its own set of pedals. Instead of the chain going to the original sprocket, it now goes on the electric drive’s motor sprocket so the motor can power the bike or you can pedal or use both.

As shown on my Giant mountain bike images, this bike has been retrofitted with a center drive 1000 watt motor, (1400 watt peak) its self contained with an integrated controller and 9 IRFB3077 MOSFETs. This controller is fully programmable with your PC, or like the Zero, minor changes made on your dash controller.  My bike is powered by a 48 volt 14AH pack that offers about 20-30 miles of range without peddling one stroke. These bikes are an absolute blast to ride and regardless of how steep the incline is they climb them with ease. These motors are available to fit most any bike.

My Giant Stance / Erad 1000 Watt Motor Drive System







The center drive has the distinct advantage over the hub motor since it uses bikes multi speed transmission (9-10 speeds mostly) for unlimited terrain advantages. In 1-3 gear, the bike has unbelievable (tractor like) power to climb and inclines up to 40 degrees or power thru sand or mud. Gear 4-7 are used for general bike riding or cruising at speeds 15-25 mph. In gears 8-9 (high gear) the bike is more geared for top speed now approaching 40-50 mph. You can shift the bike under full power since it has a shifter sense circuit which cuts the power momentarily as you shift.   

Getting back to electric motorcycles and transmissions - To appreciate the advantage of different gear ratios, after you ride these electric bicycles for a period of time, you’ll develop a skill (physical wise) for the advantage of a multi-speed gear box as you’re peddling with the motor. 

While were all aware a gearbox is not necessary for a an every day commute bike. For the guys who are hobbyist or looking for additional performance, a multi-speed transmission could offer numerous advantage. As an example, a lower ratio on our Zero would offer major advantages for off-road racing where where mud and sand are a factor on excessive draw on the motor & battery. If the bike was geared lower, the motor would be in its designed rpm and use less current. For the same reason on road applications where the bike is running at speeds at 100 mph, it would be advantageous to have a bike geared for this speed. As we all know, the “G’s” when snapping the throttle at 20-30 mph is considerable higher than that of 80-90 mph, that’s because we’ve reached the upper level of rpm’s the motor was designed for.

I’m sure the folks at Brammo had a least a few good reasons for designing the bike with a multi-speed transmission; one it would be more attractive to most bikers, and secondly offer an option for riders to select gears best for their riding environment and hopefully more range. Possibly where Brammo went wrong is by not designing a 3-4 speed transmission which would be more adaptable to an electric bike as the current 6 speed transmission in confusing and hard to shift for most riders.



In Closing - Maybe I’m way off here, but I have thought for years the best way to offer a multi-ratio on a motorcycles is on the rear wheel. Just how cool would it be to have a 2 speed gear box on the rear hub. The rear hub could have a planetary reduction gear system to lower the ratio then with a mechanical cable, you could lock it out and go back to the standard “1 to1” system like we have now.

Anyhow, at least for now, single speed transmissions are in and the slogan; “Less is More” fits the Zero’s design. What do your think?

Regards - Mike

[Richard230]

I think one of the major reasons that you don't see a two-speed gearbox on an electric motorcycle is that there are none that a small manufacturer can just buy off the shelf that would be appropriate for the application.  I am pretty sure that Brammo used a 6-speed transmission because that was all they could find that was already existing.  Even then it was likely pretty expensive to have the manufacturer design a case to fit the gearbox components that would fit into their chassis. (I bet someone lost their shirt on that deal.)

Motorcycle gearboxes are a very specialized component and if you want to have a new one designed and manufactured for you a gearbox manufacturer is going to want to know that you will be buying thousands of them, like BMW does. They apparently buy their gearboxes from an established and experienced manufacturer.  Other IC motorcycle manufacturers, like the Japanese brands, likely design and build them in-house.

I know that Zero considered installing a gearbox early on, but the weight penalty, friction losses, space requirements and especially the cost, steered them in the direction of direct-drive.  I think they made the right decision.   

[MostlyBonkers]

That's an interesting post Mike.  This is what I think:

The engineers will design an electric motor to perform well up to and including motorway cruising speeds. I believe the torque and efficiency of the Zero motors only starts dropping off above 70mph. Above that speed you're wasting much more energy to aerodynamic drag compared to any reduction in motor performance.

The torque provided by an electric motor negates the need for gears. I'm more than happy with the acceleration of my DS for my commute. It feels strong from leaving the lights and I leave the cars behind without even trying.  If I want more acceleration I can get a DSR or SR. 0-60 in under 4 seconds is lots of fun and plenty enough for all but the most determined speed freak.

So now we have a very elegant drivetrain that does the job well, why would we add complexity and give up all the benefits of not having a transmission?

There will always be special use cases where a transmission makes sense, but for the majority of people, most of the time, we're better off without one. I like the freedom of not having to change gears. It's a purer riding experience.  It's like going back to the steam age when I have to use them.

Transmissions are needed to compensate for inferior motors, mostly those of the ICE era.  That's my view.

[Erasmo]

A CVT might be a compromise between the two.

[Fred]

I'm sure more manufactures will experiment with gearboxes. Bigger companies like Honda will be working on electric bikes. They have the ability to produce an appropriate gearbox in house and the potential volumes to make use of it. They've never shied away from more complex experimental solutions.

Time will tell and I'm looking forward to when we have the choice. For now though, I think Zero have made the best call.

[Low On Cash]

That's an interesting post Mike.  This is what I think:

The engineers will design an electric motor to perform well up to and including motorway cruising speeds. I believe the torque and efficiency of the Zero motors only starts dropping off above 70mph. Above that speed you're wasting much more energy to aerodynamic drag compared to any reduction in motor performance.

The torque provided by an electric motor negates the need for gears. I'm more than happy with the acceleration of my DS for my commute. It feels strong from leaving the lights and I leave the cars behind without even trying.  If I want more acceleration I can get a DSR or SR. 0-60 in under 4 seconds is lots of fun and plenty enough for all but the most determined speed freak.

So now we have a very elegant drivetrain that does the job well, why would we add complexity and give up all the benefits of not having a transmission?

There will always be special use cases where a transmission makes sense, but for the majority of people, most of the time, we're better off without one. I like the freedom of not having to change gears. It's a purer riding experience.  It's like going back to the steam age when I have to use them.

Transmissions are needed to compensate for inferior motors, mostly those of the ICE era.  That's my view.

Thanks for the reply - I agree with you concerning the Zero’s design of simplicity which is one of its main attractions to most buyers. Coming from old school, while I appreciate the simplicity of the Zero, I would also like the option of a transmission to play with. Remember there is three classifications of riders; those who are dedicated to help the environment - those who just use their bike solely for transportation and those who like to experiment and tinker with new technology, I’m the later!

Regarding a transmission for motorcycles, as we all know, every motor is wound and designed for an optimum rpm range. We also know that if we keep the motor operating at that range of peak efficiency, it results in increased performance, less current and of course more range.   

With that said, its important to note that unlike a gas engine, if we want more performance and range we can just easily add cells to achieve it. What trying to say is; if it cost a manufacture $1000 to install a tranny in a bike to achieve the range advantage, they might be better off just installing more cells to travel 10-15% further, since the weight and cost would be somewhat the same.

Lucky for us - with new technology in motors, controllers and cells the overall performance of the Zero now rivals and in many cases exceeds the performance of its ICE competition. The 0-80 mph performance of my Zero 17 DSR exceeds that of most crotch rockets, so we really don’t need more performance and at least for myself, I have no reason to travel at 100+ mph.

The biggest advantage for electric bikes is; if we did nothing other than keep replacing new advanced cells each year in the same Zero, our bike will weigh less, have more performance and more range.

Regards!

[benswing]

For context, here is some background on this topic:

1)  As you mention in your original post, transmissions have been attempted with electric vehicles and the tradeoff went badly:
http://www.autoblog.com/2008/01/23/breaking-tesla-has-a-solution-for-their-transmission-woes-get/

2)  Brammo had a transmission for their streetbikes, but eliminated it for their racing bikes.  Rider Eric Bostrom mentioned how great the race bike was without gears:
http://www.cycleworld.com/2014/06/06/electric-vs-gas

3)  We have had this debate before (2-3 years ago in earnest) with input from the lead Brammo engineer who gave his reasons for putting gears in their motorcycles.  Overwhelmingly the sentiment was that they offer more complexity and parts that can break down as a tradeoff for a minor improvement in acceleration, top speed and/or range. 

[quixotic]

The single speed for me is superlative in very cold weather, when I drive with mitted hands that are much less agile with clutch levers than gloved hands are.

[Frank]

A transmission allows quicker acceleration with a less robust system but isn't necessary in a commuter type bike.  I considered putting one in my drag bike but went with more battery and a larger controller instead.

[Killroy]

Lightning and Alta Motorcycles are also single speed. 

I would like to see a speed and efficiency plot of the Zero motor to see what the gains would be.

[MostlyBonkers]

I find it interesting that Lightning don't use gears and their range is 0-218mph.  I wonder what the sweet spot of that motor is? There might be some clever stuff going on in the motor controller that compensates for different behaviors across the rev range.

[benswing]

Lightning and Alta Motorcycles are also single speed. 

I would like to see a speed and efficiency plot of the Zero motor to see what the gains would be.

I recall reading several years ago that gears would improve efficiency of electric motors by up to 16%.  (Not enough benefit for the tradeoff.) 

[grmarks]

If an electric bike/car has enough torque to spin the back wheel and still go 300 km/h what advantage would gears make?
All they would do is slow you down because it takes a moment to change from one to the next.
There is more drive line losses with a gearbox, so extra range is debateable based on the power/torque of the motor.
If the motor is weak then a gearbox helps, but it is much easier and cheaper to use a bigger (more powerful) motor.
Tesla went back to the drawing board and designed a better controller mitigating the need for a gearbox. They have had plenty of time to design a 2 speed box ( for the model 3) but have chosen not to.
There may be studies but how old are they and what where the motor/controller parameters?

If the motor is running in an efficient part of its rev range gears will give less range. There are so many variables to range, speed of the motor is the most important.

Reno in formula e has built there best car yet, searching for range and speed and it has no gears (or 1 if you like) they built a better motor/controller so it doesn't need gears.

I love my electric bike because it doesn't have gears.
 

[Doug S]

If an electric bike/car has enough torque to spin the back wheel and still go 300 km/h what advantage would gears make?
All they would do is slow you down because it takes a moment to change from one to the next.
There is more drive line losses with a gearbox, so extra range is debateable based on the power/torque of the motor.
If the motor is weak then a gearbox helps, but it is much easier and cheaper to use a bigger (more powerful) motor.
Tesla went back to the drawing board and designed a better controller mitigating the need for a gearbox. They have had plenty of time to design a 2 speed box ( for the model 3) but have chosen not to.
There may be studies but how old are they and what where the motor/controller parameters?

If the motor is running in an efficient part of its rev range gears will give less range. There are so many variables to range, speed of the motor is the most important.

Reno in formula e has built there best car yet, searching for range and speed and it has no gears (or 1 if you like) they built a better motor/controller so it doesn't need gears.

I love my electric bike because it doesn't have gears.

You nailed it on all points, particularly when you say "If the motor is weak then a gearbox helps...". Gearboxes are crutches for engines that can't operate down to 0 rpm and/or which have lousy torque at low rpm...a category which ICEs fall squarely into. Decades ago, when they were designing the first diesel-powered locomotives, they realized that designing a clutch and/or torque converter that could handle that kind of weight, to allow the diesel engine to start and stop the train, wasn't going to work, so instead, they created the diesel/electric hybrid. The diesel engine runs a generator which is used to power the electric motors. Since electric motors are perfectly happy at 0 rpm, no transmission, clutch, or torque converter is required. The diesel can idle when the train stops and run at its most efficient or most powerful rpm at other times.

[BertTrack]

I'd prefer a clutch to be honest.

When the backside kicks out it's nice to be able to disengage the spinning mass from the rear wheel.