Unit-swing suspension

Open the side panel of a Honda Activa, TVS Jupiter or Suzuki Access and you will see that the engine, the CVT belt case and the rear wheel are bolted together as one assembly. This is a unit-swing: instead of a separate swingarm, the engine unit itself is the swingarm. The front of the engine hangs from the frame on a pivot, usually through a short hanger link with rubber bushes, and one or two shock absorbers connect the rear of the transmission case to the frame under the seat. The same idea is used on many electric scooters, where the motor sits in or next to the swingarm.

• The rear tyre meets a bump and the whole engine unit swings upward about the hanger pivot.
• The rear shock compresses, and its damper absorbs the energy.
• The rubber bushes in the hanger soak up engine vibration so it does not reach the floorboard and handlebar.
• The spring returns the unit while the damper controls the speed.

The layout makes a scooter possible: the engine sits low under the floor, no chain or driveshaft is needed because the transmission ends right at the wheel, and the flat floor and underseat storage stay clear. The price is that the engine, which weighs as much as the rest of the scooter's unsprung parts put together, bounces with the wheel, so scooters feel busier and less settled than motorcycles over broken roads and the rear tyre skips more easily. Worn hanger bushes make the rear feel loose and let vibration through.