How Does Bike Suspension Work?
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Who Needs Suspension?
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"Bike suspension" refers to the shock-absorption system of a bicycle. Much like a car's shock absorbers, bikes have a system on board to protect the rider from feeling every bump and dip during a ride over rough terrain.
"Suspension" refers to the mechanisms that connect the front and rear wheels to the frame of the bike. The suspension on mountain bikes and hybrids (combination off-road and street bikes) have two parts, including the front fork and the rear suspension.
A Bumpy Ride
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Without a suspension, a bike rider would be in for a very bumpy ride. Every bump, dip and rough spot would transmit directly to the rider, making for a jarring trip. Instead, bikes have suspension to limit the rough ride. Most bicycle suspensions have two parts: a spring and a shock absorber. Bikes can either have spring-, air- or oil-filled suspensions.
The rider can control the suspension settings on most bikes. "Suspension travel" refers to the complete allowable up-and-down movement. "Preload" is the amount of force that is applied to the spring with the rider's weight on the bike. Both settings adjust the overall bouncing motion of the bike to create a comfortable ride.
For example, say a rider drives over a rough spot. What does the suspension do first? The suspension fork at the front and rear wheels contains a spring that is set specifically with travel and preload for the rider. He hits the bump, and the suspension compresses down with the movement while keeping the rider and frame of the bike relatively stationary.
Abosorbing the Shock
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One a rider hits a bump and the suspension begins its compression, another mechanism comes into play. Damping is the actual shock-absorbing system that slows down the spring motion and absorbs the energy of the spring. Something needs to absorb this energy and control the return rate of the spring. Damping is that control.
The damper is the actual shock absorber of the suspension system, and is controlled at the fork of the wheel. It can either be based on friction or dampening can occur via a piston mechanism housed in an oil-filled chamber (much like a car's shock absorber). As the piston compresses, energy is absorbed by the piston, forcing oil through a small hole. In general, if you are traveling over continually bumpy terrain, you want the fork to return to position more quickly to absorb the next movement.
Back to Normal
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"Rebound" is the rate of return--the time the suspension takes to return to its regular position. Rebound should always be adjusted specifically for the terrain. If it isn't, your suspension will not have enough time to recover for the next bump. Rebound refers to both the overall rate of spring return and the rate at which shock absorbers return to their original position.
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