HOW SUSPENSION FORKS WORK

Just what is going on inside those bouncy bits on the front of your bike?

Chassis

This is the external ‘frame’ of the fork, which provides the structural rigidity necessary to optimise suspension performance. Essentially, forks are made up of a pair of aluminium upper tubes (‘stanchions’), which are surface-treated to reduce friction. These slide inside cast magnesium lower tubes, which are fitted with bushes so that the two sections can glide past each other with minimal friction and without rattling around. Any bending, twisting or flex in the tubes will prevent the stanchions from sliding freely into and out of the lowers, so a strengthening arch at the top and a boltthrough axle at the bottom are used to increase stiffness. The stanchions are held in place by the crown, which also has the steerer tube pressed into it, to attach the fork to the frame. Forks with widerdiameter stanchions (35-38mm) tend to be stiffer, so they’re used for more aggressive riding such as downhill and enduro, but could be overkill for trail and cross-country use.

Springs

Most suspension forks use air springs, although metal coil springs are still available, and there are pros and cons to each. The job of the spring is to support the rider and bike’s weight, and absorb the energy from bumps and impacts, to smooth out the trail and help keep the front tyre in contact with the ground. High air pressure or stiffer coils provide more support; lower air pressures and softer coils give less. Getting the correct spring rate (air pressure or coil rate) for your weight and riding style is crucial for optimal suspension performance.

Damping

The damping determines how fast the spring can move to absorb the bump or impact energy. Without it, a fork would feel bouncy and uncontrolled. There are two types of damping in a suspension fork – compression damping, which controls how the spring compresses during an impact, and rebound damping, which comes into play when the fork re-extends. Generally, when you compress a fork – by pushing down on it, riding over a bump or landing from a jump – oil is forced through tiny holes (‘ports’) and over washers of different sizes and thicknesses (‘shims’) to slow the spring down slightly. External damping adjusters allow you to open and close these ports, or tweak the amount of force needed for the oil itself to open/close them, in order to change the speed at which the oil flows and thus determine how fast the fork will compress. The same is valid for rebound damping.

Linkage forks

Linkage forks still have a spring and damper, but differ from conventional ‘telescopic’ forks (such as the Fox 34 below) in both looks and operation. Instead of relying on sliding tubes to deliver their suspension travel, they use a system of links and pivots, a bit like the rear end of a full-suspension bike. The main advantage of linkage forks is reduced friction (because they don’t require the bushings and seals of a telescopic fork). Also, the manufacturer has some control over the wheel path, so the best designs are better at absorbing some

– but not necessarily all – bumps. They tend to be pricey, though, and not everyone likes the ride feel.