The concept of preload is simple. Motorcycles, unlike cars, don’t tend to weigh too much more than their operators. A 200-pound man in a 3800-pound car is one-twentieth of their combined weight of 4000 pounds. A 200-pound man on a 600-pound motorcycle is one-fourth of the total weight (800 pounds) of both rolling down the street. Manufacturers take this into consideration and the bike should still handle well. Now, put that guy’s 250-pound girlfriend and gear combo on the back (Sturgis anyone?) and the total weight is 1,050 pounds. The suspension is now under a load that is over two-thirds the weight of the bike alone. Someone might want to let the suspension know this prior to pulling into traffic. Preload adjusts the suspension to compensate for the larger load. (Motorcycle engineers are awesome!) Typically, an adjustable mechanism compresses the spring that surrounds the shock slightly, making it “stiffer.” The result is that the suspension is better able to handle the forces applied by the added weight. A further benefit is the geometry of the motorcycle is kept nearer to its ideal position.
The motorcycle’s geometry is important to operational safety. In a situation where a bike is loaded heavily to the rear, one will likely end up with a front-high, tail-low posture. Shining your headlight off the road and into the trees, or into the eyes of some 16-year-old coming at you on his first night out with his shiny new license may be a concern. If not, there are other factors to ponder.
Maneuvering and braking performance in this circumstance will suffer, especially in an emergency. Relatively little braking power comes from the rear wheel, yet much of the overall mass would be situated nearer that point. The forks would have to load up (compress) prior to the front tire traction being sufficient to accommodate the braking forces necessary during an emergency stop. That takes valuable time and distance. In an evasive turning maneuver, the front tire could be more susceptible to “washing out” due to the aforementioned lessened handling characteristics when trying to change the direction of all that rearward mass. Braking and swerving involve the dynamic changing of speed and direction, otherwise known as a vector. This can spell double-barrel havoc in those moments when you need every ounce of help you can get. In an emergency you don’t need your bike working against you. Having the bike sitting properly really helps level the playing field (pun intended).
Leveling the bike means looking up front sometimes as well. Some motorcycles, such as BMW’s, have preload adjustment in the front suspension. The ability to adjust the front suspension translates into improved handling. But, not every bike is designed for preload to be adjusted easily up front. Sometimes the only way to adjust the forks for load is to change-out the fork springs or even the entire forks, usually, this is done as an upgrade by those who know they’ll be riding heavy a lot of the time. However, more and more manufacturers are allowing for the adjustment of rebound and compression both up front and in back. These adjustments address how the suspension responds moving into and out of a loaded condition.
Remember, be it riding solo, two-up, laden with gear, or whatever combination thereof, adjusting the preload on a motorcycle can help it handle better and more safely. Folks who are unfamiliar should consult their owner’s manual on adjusting the suspension settings for their specific machines. Dealerships, mechanics, and even online tutorials can provide valuable insight and instruction for proper suspension setup. Don’t be afraid to adjust and readjust to your liking. Make adjusting the preload part of your pre-ride check. Make it a habit.
Text and Photography: Charles Neeley
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