There is a new category of automobile technology that doesn’t yet have a motorcycle equivalent, and it’ll be interesting to see if one will appear. The Chevy Volt is currently the leading example of this rare breed of car. It’s technically a “hybrid” in that it has both an electric motor and a gasoline engine. But that term, when applied to the Volt, is a bit confusing, in that most other hybrids, while having electric motors and internal combustion engines, also have drive systems for each power system. The Volt doesn’t.
Even Chevy doesn’t seem to have decided what to call the Volt. You may have heard terms like “parallel hybrid” and “series hybrid,” but these do little to explain the technology to non-engineers. So, I’m going to go out on a limb and create a name for it. I call it a Bat/Gen Electric. It’s an electric car with a motor driving the wheels. Its battery has enough capacity to allow 38 miles of range on a charge. When the charge gets low, a gasoline engine driving a generator creates enough electrical power to keep you going. It’s an approach that makes a lot of sense, as a dead battery doesn’t strand you by the side of the road. The Volt has about 300 miles of total range before both the battery and the gas tank are “empty.” Plus, the Volt can be plugged in at your home to recharge the battery—you could go days without ever having to use the gas engine.
There are enough battery-electric motorcycles in production or in development to give us a lot of information. If there are bat/gen electric motorcycles in development, they’re still mostly under the radar. But we can take a look at the Volt and do some extrapolation to get an idea of what we might expect from a bat/gen electric bike.
Comparing the Volt and a more or less equivalent internal-combustion car will allow us to see how a bat/gen bike might compare to a competitor’s gas-powered motorcycle. The new Honda Accord is in roughly the same size and performance class as the Volt, so let’s see how those compare. The Volt’s combined horsepower is 149 against the Accord’s 185, but the Volt pounds the Honda on torque, 273 lb.-ft. max vs. 181. Estimated mileage is 95 city/93 highway for the Volt, 27/36 for the Accord. But the Volt weighs 3781 pounds against the four-cylinder Honda’s 3192. And then there’s the price tag: The $39,000 Volt is $11,000 more expensive than an Accord at a similar trim level.
But the Volt’s maximum performance happens at full charge, and things start to look different at 38 miles or so when the battery nears depletion. The generator motor makes only 84 horsepower, so without the battery to help out, that’s all the power available (less power losses of at least a few percent). With a discharged battery in the Volt, you’re still driving, but you’re driving a very different car.
What would we see if a bat/gen electric motorcycle were to appear? Based on the numbers here, we might expect a bike that’s 40 percent more expensive and 20 percent heavier than a similar internal combustion model. Operating in battery-electric mode, power and torque would certainly be adequate if not truly sporting. Once in generator-electric territory, power would almost certainly be substantially reduced.
Automotive parallels are, however, an unreliable measure of what we’d see once the technology appears in bikes. As every motorcycle designer knows, packaging space on a bike is at an absolute premium. It’s true of gas bikes, where issues like noise and emissions demand ever-increasing volumes for mufflers and airboxes. It’s certainly true of battery-electric bikes, on which virtually all non-chassis space not taken by the motor, drive components, controller, cooling system, and electronics is used for battery volume.
Looking at the packaging density of battery-electric motorcycles, it’s obvious that the addition of a complete generator assembly that must include the generator, a gasoline engine to drive it, and all the accessories like fuel tank and exhaust system, is going to be a challenge.
The bat/gen electric vehicle is a logical answer to the limited range of a battery-electric. The compromises necessary to carrying a generator along with your electric vehicle seem to be at least marginally acceptable in the automotive context. The motorcycle application will be even more challenging. Increases in battery power density and other efficiencies will help, but for now the challenges look prohibitive. I’d love to be proven wrong.