Raising the Height of a Motorcycleby Chris Gilliland
A motorcycle's overall height plays a big part in the machine's steering habits, but it also lends to the rider's confidence, especially at a complete standstill. For many smaller riders, having the bike lower to the ground allows them to plant both feet firmly on the asphalt. However, other riders may prefer to raise their motorcycle for a number of reasons.
Understanding Steering Geometry
A motorcycle is literally built from the ground up, using a complex set of equations, called steering geometry, that determine how the motorcycle interacts with the road. Most motorcyclists have heard of rake, trail and wheelbase, which denote the angle of the motorcycle's front fork, how far the front tire's contact patch is from the rake and the motorcycle's overall axle-to-axle length. All three elements play a part in the motorcycle's straight-line stability and maneuverability. Increasing the rake, as seen on a chopper-style bike, pushes the fork outward, extending trail and wheelbase in the process to create a stable ride, but this decreases maneuverability substantially. Conversely, sport bikes use less rake, and therefore have smaller tail and wheelbase figures, resulting in highly maneuverable bikes less stable in a straight line.
How Height Affects Steering Geometry
At first glance, the height of a motorcycle would appear to matter very little to the machine's steering traits. However, raising a motorcycle at either its front fork, rear swingarm or both will alter its rake, trail and wheelbase. Used correctly, these changes can provide beneficial enhancements to the motorcycle's steering traits. For example, raising the rear of the motorcycle by as little as 10 millimeters will decrease the wheelbase and the rake, allowing the motorcycle to turn faster with less effort required from the rider. But raising the front fork by the same amount will do just the opposite, increasing rake and wheelbase. This results in more stability, especially at higher speeds, at the cost of increased effort to initiate and maintain a turn.
The Purpose of an Increased Height
The reasoning behind a rider's choice to raise his motorcycle's height will depend mostly on the type of riding he uses most. A cruiser-type motorcycle, typically lower to the ground, can easily bottom out over larger bumps and dips, allowing the motorcycle's frame and engine to make contact with the road below. Increasing the height of this particular motorcycle would increase ground clearance, preventing road irregularities from becoming a problem. Conversely, sport bikes will gain considerable maneuverability boosts by raising the rear of the motorcycle slightly. This will allow the rider to tailor his motorcycle's steering habits to the needs of the racetrack or road on which he is riding.
How to Increase a Motorcycle's Height
More and more of today's motorcycles are equipped with adjustable suspension, which provides provisions to increase ride height through spring preload, or the preset amount of compression placed on the fork or shock absorber's spring. This allows for some adjustment up or down but will affect the quality of the motorcycle's ride. Increased spring preload lowers the bike and makes the ride feel harsher, while decreasing the preload raises the bike and softens the ride. As an alternative, the link that connects the rear shock absorber to the motorcycle's frame can be replaced with a shorter, aftermarket raising link. This will increase the height at the rear of your motorcycle, while still providing complete control over the spring preload.
- The Professional Motorcycle Repair Program: Frames, Suspension and Steering, Volume 21; Professional Career Development Institute
- Motorcycle Dynamics; Vittore Cossalter