All vehicle suspensions have 2 general parts: a spring, and a shock absorber or damper. These 2 parts are placed between some component that moves (a swingarm for the rear and a fork leg for the front) and some component that doesn’t (the frame/chassis). The suspension controls wheel movement for rider comfort and better handling. Even the most basic motorcycle suspensions usually allow for some adjustment, especially to the rear suspension’s preload. Motorcycle suspension springs are designed so that they’re always under compression—and how much compression is a function of preload. Measure an uninstalled spring with no compression on it—that’s called the spring’s free length. When you have to compress that spring to install it, you’re pre-loading it. At the rear, a ramped-collar adjuster is the simplest method—turning the collar in one direction pushes it down harder on the spring, pre-loading it more. Another method is to use a collar that screws down the shock body, compressing the spring. For fine-tuning, some sportbike shocks use a hydraulic adjuster—in that case, you can just spin a knob to adjust your preload.