When they're taking on off-road terrain, ATVs tackle a lot of bumps, ruts, slopes and obstacles. If you're racing your ATV or hitting the trails aggressively, you might even catch air. A solid suspension is crucial to absorbing that kind of punishment, and shocks and springs do the heavy lifting.
ATVs shocks use a reservoir filled with oil to resist compression of the suspension. The spring, which usually coils over the shock, also resists compression and pushes the suspension back to its original position. There are two important variations among ATV shocks: how adjustable they are and where the oil reservoir is located.
If the oil reservoir is inside the shock itself (known as a monotube design) the oil is prone to heating due to the friction of the shock's travel. This heating makes the oil foam and can seriously reduce the effectiveness of the shock. The stock shocks on most ATVs are of this type.
If you want to upgrade, look for shocks with a separate reservoir. The reservoir may be attached to the shock (known as a piggyback design) or totally separate, connected by a hose and suitable for mounting anywhere on the vehicle's frame (known as a remote design). The reservoir introduces additional oil to the shock body, keeping it cool.
Adjustability is important not just for high-performance ATV racing, but for comfort. There are three main adjustments that can be made to ATV shocks: compression, preload and rebound. All ATV shocks let you adjust preload (how compressed the springs and shocks are without hitting any bumps), but only high-end shocks allow compression and rebound adjustments.
Take a look at all the attachments and accessories you can use with an ATV in the next section.