Motorcycle.com has put together two absolutely stellar pieces. One, if you’re new to all this, is the definitive Electric Motorcycle Primer, here. Really, I’m pissed I didn’t do it myself, but they can bring to it a whole lot more authority than I can. In it you can read about both the short history of production electric motorcycles, some discussion of the realities of the electric drivetrain, discussion and comparisons brands and models, and also gas bikes, in a good, measured, objective bit of narration. Congrats, and thanks to Jeff Cobb and Troy Siahaan.
I don’t care who you are. Read it. You’ll learn something.
The other piece addresses (and answers) many, many questions about transmissions in electric drivetrains, by way of a 2013 model comparison between the Zero and the Brammo Empulse, by Tom Roderick. Read that for whatever you’re interested in, but what I’m looking for are some cold, hard facts about transmissions in electric motorcycles. That is, is there an advantage, or a disadvantage to running a transmission? How does a transmission affect the ride experience? Does it affect the range? For two similar bikes with comparable specs, will a transmission be quicker? (acceleration) Will it be faster? (top speed)
So. Here’s what they say:
- The Brammo off-the-line acceleration is quicker. Even though the bike is 80 some-odd pounds heavier it is clearly out-accelerating the Zero. 80lbs is a lot, and probably more than just the additional weight of the transmission (which I guess is around 40-50lbs) so that is a clear, conclusive fact. By distributing the torque curve of the electric drivetrain – admittedly much wider than a gas engine – you are getting more torque off the line, and more torque at the top end. You’re keeping your top speed of around 100mph, but able to pull off the line. The Zero, like any bike without a transmission, has to compromise between gearing that gives you good acceleration off the line, and the top speed. You can gear it high to get faster top end, but it’s going to overload the motor and bog off the line.
- That said, 6 gears is probably too many. After a few years of hashing the subject out on the forums, the conclusion I came to was that you maybe need 2 speeds, OK, three. Motorcycle.com agrees: “After now having twice tested the Brammo Empulse R we are convinced that six gears is, at least, three gears too many. It’s our opinion either a Low/High or Low/Mid/High transmission will more than suffice.”
- The interesting surprise is the Zero’s better “roll-on” performance. This is likely due to the lighter weight, since the motor, at high speed, is now spinning fast enough to overcome any low-speed loading issues. This is interesting because, apparently, you can hammer out of a curve better on the Zero than the Brammo, even with the ability to downshift the Brammo. I’m not sure what to conclude from this, except that, once you’re rolling the benefits of a transmish may be lessened.
The Questions Unanswered:
There are a few nitty little details I still have questions about.
- First, the Zero has better range. A big part of that is the larger battery pack it’s sporting, but there’s also the parasitic losses of the transmission. Some sources have said a six-speed transmission saps about 10% of your power. The Brammo is heavier, has a transmission, and has a smaller pack… which of these factors, if not all of them, are directly due to the transmission?
- OK, let’s settle on one point – using a transmission gives you the ability to spread the torque around and give you better acceleration while maintaining your top speed, on two bikes of similar weight and size, as well as cost. That begs the question, what happens when you put in a bigger motor and more battery power instead of a gearbox? That’s been a common angle to the argument for quite some time, and it’s a hard one to address, but the point is that adding a transmission is in some way an engineering “band-aid” for running a smaller motor and lower voltages. The problem with this argument is it’s basic logic. If a transmission helps optimize a smaller powertrain, it’s got to help optimize a big one too. We’re not arguing about making a faster bike. We’re arguing about whether a transmission can make any bike faster.
- Cost. How much of the higher cost of the Empulse is the transmission? At a $3000 difference, I’m thinking about 1/4 of that spread is the tranny, but I don’t know. The Brammo clearly has better chassis components, giving it far superior handling, which probably accounts for the lion’s share of the price gap.
Of course, every answer just creates more questions, but this goes a long way to helping us understand the principles of the electric drivetrain. What will help even more will be to see some results on the track…