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Rear suspension

Mountain biking – being highly competitive in sporting, technology and commercial terms – boasts as many different rear suspension designs as it does bike companies. And each proud designer knows their beautiful baby blows the others away. While the models differ in detail, it is possible to divide the majority into three types: cantilever, linkage, and URT (unified rear triangle). All three rise and fall in popularity over time. Within each type, there are bikes that have been designed with computer-aided wotsits and cutting-edge doodahs but still ride like dogs. Meanwhile, those you heard a convincing argument against last week still feel fast and furious.

Choosing a suspension bike can be stressful. Anybody with any experience has an opinion on what suspension you should consider, and they’re all different. However, out there is a bike designed by someone who wants the same from a ride as you do. My advice is try to ride as many different designs as you can before making a decision.

The appropriate design for you depends on your build and riding style. Some people sit in the saddle as long as possible, using their energy economically (they might have a road-bike background). They may generally dislike designs where the position of the rear end affects the chain length, snapping back as they pedal. Others, maybe with a BMX or trail bike background, are up and out of the saddle with little excuse, using their shoulders and their body weight rather than their legs to propel the bike. They may waste loads of energy, but they like great short bursts of power.

Fox Float suspension unit

Fox Float suspension unit

Rear suspension design has two elements: frame shape and shock characteristic. All frames are based on the principle that the rear part of the frame is hinged so that the rear wheel moves relative to the main body of the frame. A lot of thought goes into manipulating the pivot and strut positions that make up the rear end in order to control the axle path (or, the position of the axle relative to the frame as it moves through its travel).

Trail forces come from different directions. When you land from a dropoff you apply force directly upwards, and if this were the only force on the rear wheel the equation would be much simpler. But you’re also driving the back wheel by pedalling, applying force to the wheel along the horizontal, along the chain from chainring to sprocket. If the hinge between the back and front of the bike lies between the chainset and the rear axle, then pedalling activates the suspension. The movement of the rear end as it reacts to the terrain causes movement in the pedals – ’chain reaction’. This isn’t always a bad thing; in climbing, the pedalling tends to extend the suspension and dig the back wheel into the ground, giving you extra grip. Chain reaction is not so alarming, as long as it isn’t huge. Your feet get familiar with dealing with the effect quickly, until you don’t notice it. Successful suspension design makes the rear axle as responsive as possible to uneven terrain, while minimizing the extent to which pedalling compresses the shock and wastes your energy.

Once the frame has been constructed, the task of the rear shock is to control the speed at which the rear wheel moves along its axle path under force. The spring in the shock absorbs force, while the damping ensures that the spring re-extends at a controllable speed and doesn’t buck you off the saddle. A perfect shock responds to small forces instantly, making the bike feel supple and helping to find whatever grip there is. It can also take a big blow without reaching the limit of travel.

This is a lot to pack into the back end of a bicycle, especially when, at the same time, people want everything to be light, strong, stiff and painted this week’s hot colour. Small wonder there are as many different ’perfect’ designs as there are designers. The evolution of suspension design has taken place in fits and starts, with some folks charging down cul-de-sacs and others beavering away to refine proven designs. There is no right answer, and thus it would be a shame to waste too much riding time wondering if your pivots are in the ’right’ position.

See also bike maintenance tips, tricks and techniques “RockShox Reba: 50- and 100-hour service”