Twin shock absorbers

Twin shocks are the traditional rear suspension of the commuter motorcycle and are still fitted to India's best sellers: the Hero Splendor, Honda Shine, Bajaj Platina and the Royal Enfield Classic 350 and Bullet, as well as to some scooters. The rear wheel is held in a swingarm that pivots on the frame behind the engine. Near each end of the swingarm, close to the axle, a shock absorber, a coil spring wrapped round a hydraulic damper, runs up at a slight slant to the frame under the seat.

• The rear tyre rises over a bump and the swingarm swings up about its pivot.
• Both shocks compress together: the springs store the energy and the dampers push oil through valves to absorb it.
• Because the shocks sit close to the axle, they move almost as far as the wheel does, so they can be short and simple.
• The springs push the wheel back to the road and the dampers control the return.
• A notched collar at the base of each spring lets the rider set preload for a pillion or luggage.

The rider notices a simple, predictable ride that is comfortable over normal roads but can bottom out over a deep pothole with two people aboard, because the springs are usually not progressive. Twin shocks are cheap to make, easy to replace, and leave the centre of the bike free for the airbox and battery, which suits a commuter. Some models offer gas-charged or adjustable units as an upgrade, and the Royal Enfield units show how well damped a modern twin-shock setup can be.