Bicycle suspension is the system, or systems, used to suspend the rider and bicycle in order to insulate them from the roughness of the terrain. Bicycle suspension is used primarily on mountain bikes, but is also common on hybrid bicycles. Bicycle suspension can be implemented in a variety of ways, including front suspension, rear suspension, suspension seatposts, suspension saddles, and suspension stems (the latter now uncommon).
Bicycles with only front suspension are referred to as hardtail, and bicycles with suspension in both the front and rear are referred to as dual or full suspension bikes. When a bicycle has no suspension it is called rigid. Besides providing comfort to the rider, suspension systems improve traction and safety by helping to keep one or both wheels in contact with the ground.
History
As early as 1885, the Whippet brand of safety bicycle was notable for its use of springs to suspend the frame. In 1901, author and engineer Archibald Sharp patented air suspension for bicycles. In 1983, Brian Skinner designed and implemented the first suspension system for a mountain bike with a simple rear shock and a single pivot called the MCR Descender. Front suspension appeared on bikes in 1990 when Doug Bradburry designed and built a front suspension fork using elastomers with no dampening effect. The first full-suspension folding bike from German engineers Riese & Müller was developed in 1992 and launched in 1995 as the Birdy model.
Front Suspension
Front suspension is most often implemented using a telescopic fork. The specifics depend on the type of mountain biking and are generally categorized by the amount of travel. Forks consist of two main parts: a spring (steel coil, titanium coil, compressed air, or elastomer) and a damper (typically forcing oil through small orifices or shim stacks). Travel has increased over time: 80–100 mm was once sufficient for downhill bikes, whereas downhill forks now typically offer 200 mm or more.
Alternative front suspension designs include Cannondale's HeadShok (shock built into the steerer tube) and Lefty (single-sided fork), as well as four-bar linkage forks from Proflex (Girvin), Whyte, and BMW (Duolever).
Rear Suspension
Rear suspension designs have evolved significantly since the early 1990s. Key types include:
- Soft tail: Relies on flexing of the chainstays, with a shock absorber in line with the seat stays. Limited travel (typically 1–2 inches).
- Unified Rear Triangle (URT): Bottom bracket and rear axle are directly connected; suspension action occurs between the rear triangle and front triangle. Prone to suspension bob.
- Single pivot: One pivot point connecting the rear wheel to the main frame. Simple but can suffer from brake jack and regressive suspension rates.
- Linkage-driven single pivot: Uses extra linkages between the swingarm and shock to optimize the suspension rate.
- Split pivot: A special case where one four-bar pivot coincides with the rear axle, allowing the brake caliper to be mounted on the floating linkage.
- Horst link: A four-bar linkage suspension characterized by both connecting links pivoting on the seat tube. Patented by Horst Leitner and now used by Specialized (as "FSR Suspension") and others.
- Short link four-bar: Includes Virtual Pivot Point (VPP), DW-link, Giant Maestro, Switch link, and Trek Full Floater designs.
Seatpost Suspension
Suspension may be implemented at the saddle using a suspension saddle, suspension rails, or a suspension seatpost. Designs include piston-style (sliding post with spring pressure) and parallelogram-style (dual linked bars connecting the saddle clamp to the post). This style is most popular on upright bicycles where the rider spends the majority of time seated.
Terminology
- Travel: How much movement a suspension mechanism allows, usually measured at the wheel axle.
- Preload: Force applied to the spring component before external loads (e.g., rider weight) are applied.
- Rebound: The rate at which the suspension returns to its original configuration after absorbing a shock.
- Sag: How much a suspension moves under the static load of the rider alone.
- Lockout: A mechanism to disable suspension, making it substantially rigid (useful during climbing or sprinting).
- Bob and squat: How rear suspension responds to pedaling; both are undesirable characteristics that rob power.
- Pedal feedback: Torque applied to the crankset by the chain caused by motion of the rear axle relative to the bottom bracket.
- Compression damping: Systems that slow the rate of compression in a fork or shock.
- Unsprung mass: The mass of portions of the bicycle not supported by the suspension systems.
Applications
Mountain bikes are the most common application, with many using full suspension. Notable suspension fork manufacturers include Manitou, Öhlins, Marzocchi, Fox Racing Shox, RockShox, X-Fusion, RST, Suntour, and Magura.
Road bikes rarely incorporate suspension, though some models (e.g., Trek's s.p.a. system and Alex Moulton bicycles) have used it.
Recumbent bicycles often have at least rear suspension because the rider is usually unable to lift themselves off the seat while riding.
