Telescopic fork

The telescopic fork is the front suspension of nearly every motorcycle and most scooters sold in India, from the Hero Splendor and Honda Shine to the Royal Enfield Classic 350 and the Honda Activa. Each of the two fork legs is a pair of tubes: the thin inner tube, or stanchion, is clamped in the triple clamps under the handlebar, and the thick outer tube, or slider, carries the front axle. Inside each leg is a coil spring, a quantity of oil and a damper rod with small holes.

• The front tyre hits a bump and the outer tube slides up along the inner tube.
• The coil spring inside compresses, storing the energy.
• Oil is forced through the holes in the damper rod; the resistance slows the movement and turns the energy into heat.
• The spring extends again and oil flows back through a different set of holes, usually slower, so the front does not spring up too fast.
• An oil seal at the top of the outer tube keeps the oil in and a dust seal above it keeps grit out.

The rider notices the fork dive under braking, which shifts weight onto the front tyre and is part of how a bike steers. Spring stiffness decides how far it dives; oil viscosity and the damper holes decide how fast. Bigger stanchions resist flexing better, which is why sportier bikes quote fork diameters. The tubes must slide freely, so a bent stanchion, a pitted chrome surface or a leaking seal ruins the action and is the most common fork repair.