How a Swing Arm for a Bike Works
A motorcycle's suspension serves a dual role, providing the rider with control of steering and braking while also absorbing the road conditions to give a more comfortable ride. The suspension components consist of fork tubes on the front of the bike and a swing arm in the rear. The swing arm is the main component of the rear suspension and also provides a base for the rear axle to be mounted.
The swing arm is joined to the motorcycle at a higher pivot point than where the rear axle is connected. This works to prevent squat in the tail of the bike when you accelerate and helps to provide adequate spacing for the shocks to function. When the rear brakes are applied, the swing arm is pulled level with the road. This lowers the pivot point where the swing arm joins the bike frame and lengthens the wheelbase at the same time, making the bike more stable and easier to control.
There are two types of swing arms found on most bikes. Typically, most bikes have what is referred to as a monoshock regular swing arm. In this design, a coilover shock is joined to a linkage that is connected to the bike frame and the H-shaped swing arm itself. A newer version is the single-sided swing arm. This type is similar to the H-shaped swing arm in function and design, except that one side has been removed so a tire can be easily changed.
The shock absorber is the main component of the swing arm. A single shock absorber system is mounted toward the front of the rear swing arm and connected to the bike with a pin on top and a multilink set up on the bottom. The multilink helps to further deflect the shock from the road surface. With this design, the mounting of the shock absorber closer to the pivot point means less deflection for the shock.
Many motorcyclists extend the swing arms on their bikes. As the wheelbase lengthens, the motorcycle becomes more stable in a straight line. This, however, tends to affect the maneuverability of the bike, mainly your ability to steer going into as well as coming out of turns. Eric Everson of Biker Awareness suggests an extended swing arm that adds 3 to 5 inches to your original swing arm length as a means of gaining straight-line stability without losing steering power.
The pivot points of swing arms and the shock absorbers are exposed to the rain, dirt and dust when riding. There are grease fittings that should be lubricated regularly. To grease these points, you can purchase a grease gun and grease at your local auto or motorcycle care stores. Pumping the gun forces in fresh grease and pushes out old, dirty grease.
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