Born to be Mild

A new automatic transmission lets newbies tear up the road without grinding up gears

Engineers have tried and failed for decades to build motorcycles with automatic transmissions. Honda finally gets it right with the new DN-01 “sports cruiser” bike. Conventional automatic transmissions, like those in cars, lag when you hit the throttle and can throw a bike off balance during turns. Honda’s HFT (for Human Friendly Transmission) responds to the throttle instantly by using hydraulic pumps instead of standard gears.

The HFT offers a range of gear ratios similar to a conventional six-speed manual, and it has about the same weight and dimensions. The motorcycle goes on sale in Japan this year, though a price has not been set. Honda hasn’t yet decided if America’s weekend rebels will get their own auto-shifting bike.

Launch the gallery to see how Honda’s truly fluid transmission works.

Honda DN-01 Transmission

Honda DN-01 Transmission (step one)

1. The engine cranks a pump that turns both the drive shaft and a tilted metal disk [A].
2. As the disk spins, it depresses a circular set of pistons [B] around the shaft.
3. The pistons eject high-pressure fluid that travels through a chamber [C] and pushes out a second set of pistons [D].
4. Those pistons press a second tilted disk [E], causing it to spin and transmit extra torque (leverage) to the drive shaft.

Honda DN-01 Transmission (step two)

5. A motor adjusts the angle of the second disk . A lot of tilt provides the high torque found in low gear [F]. Less tilt offers lower torque but more speed, like a high gear.

Honda DN-01 Transmission (step three)

6. When the disk isn’t tilted [G], the second set of pistons shuts off to save power, and the pump alone turns the shaft and rear wheel.
Dan Carney

Dan Carneyhas been riding motorcycles and driving cars since before it was technically legal for him to do so. Along the way he has picked up automotive journalism awards from the International Motor Press Association and Washington Automotive Press Association for his work, and he wrote books about two significant sports cars, the Honda S2000 and Dodge Viper. He has been a PopSci contributor since 1998.