Electric Bikes Race - Watt's Up?

Drawing The Line

The TTXGP was a world first: a "zero-carbon" motorcycle race held during the Isle of Man TT races this past June. Though the race wasn't limited to electric bikes, only electrics showed up, and it became a demonstration of the 2009 state-of-the-art of two-wheeled electric vehicles.

The race was held over one lap of the 37.73-mile mountain circuit. The winner was Rob Barber, riding the Team Agni bike at an average speed of 87.4 mph. The lap record for internal-combustion engines now stands at 131 mph, so the electric bikes are relatively slow. In 1935, Stanley Woods lapped a Moto Guzzi at a record 86.5 mph, so we have to go back almost 75 years of internal-combustion development to match Barber's speed.

Electric vehicles have been around since the 1830s and have been in constant development since, with trains seeing the most progress. Electric-train speeds have increased radically, to the point that the French TVG has recorded an impressive 360 mph. But trains have a constant supply of power from electric rails or overhead cables, while electric bikes and cars carry their power on board. Batteries are the "choke point" of such electric vehicles, and when you understand more about these power sources, an 87-mph lap starts to look pretty impressive.

The Team Agni bike is a Suzuki GSX-R750 fitted with twin electric motors made by the Agni Company in Bangalore, India. These are DC brush-type motors, air-cooled without fans. The motors attach directly to a cross-shaft holding the drive sprocket, and a conventional chain runs from that to the rear wheel. There is no clutch or transmission. The battery is a group of lithium-ion cells that have a capacity of 16 kilowatt-hours.

How much energy is that? One kilowatt-hour equals 0.027 gallons of gasoline, so 16 kW-h multiplied by 0.027 equals 0.43 gallons. Since an electric motor is much more efficient than a gasoline engine, you need to multiply the gallons by the efficiency ratio to get a real comparison. The Agni motors, depending on rpm, are between about 65 and 90 percent efficient, while a gasoline engine is maybe 25 percent efficient, making the electric about three times as efficient overall.

Multiplying the 0.43 gallons by three gives 1.3 gallons. So the Agni is carrying the equivalent of 1.3 gallons total. If the Agni used 90 percent of its energy in one race lap, it used 1.17 gallons over the 37.73 miles and got the equivalent of about 32 mpg. That corresponds with what you might get riding a conventional gasoline-powered streetbike at a near-90-mph pace over a winding, hilly road.

The Agni motors together made about 40 to 50 horsepower during the lap and used most of the battery power available. Putting bigger motors on the bike would have improved the speed but depleted the batteries faster, risking a non-finish, so the match between motors and batteries was good. Carrying more battery power would allow a bigger motor, but lithium-ion batteries with 16 kW-h capacity are likely to weigh about 220 pounds and take up 45 liters of volume. So even if you can find the space for more battery power, the weight would add up.

The performance of electric motorcycles is sure to improve significantly. Most important will be smaller, lighter, more powerful batteries. More power from the motors really isn't a problem as powerful, lightweight motors are available now. Most electric-vehicle developers have stayed with the simplicity of one-speed transmissions or direct-drive setups, but multi-speed transmissions will give the same benefits to electric vehicles that they give to gasoline-powered vehicles.

The Agni is very slow off the line with its overall drive ratio of about 3.5:1 (motor speed to rear-wheel speed). A sportbike's overall first-gear ratio is about 10:1, and electrics will need similar ratios to match current acceleration numbers. Multiple ratios will also permit the motor to spend more time in its most efficient rpm range, as an electric motor's efficiency tends to drop off dramatically at high rpm.

The world's first electric motorcycle race is now in the record books, and several companies are looking to take over Agni's top podium step at the next one. Development in a relatively new field proceeds quicker than in a more highly developed one, and so we're likely to see new ideas and prototypes abound. Bring it on!

Team Agni's Rob Barber won the inaugural emissions-free TTXGP at an average speed of 87.4 mph.