New stuff pops up on the trails every year during Moab's Easter Jeep Safari. From winches to crawler boxes, if it's new and exciting, it's bound to be in Moab on the trails the week before Easter. During EJS '07, Donahoe Racing's Class 3 FJ Cruiser garnered plenty of stares in Moab. The FJ, fresh off of a class win in the SCORE Baja 250, crawled just as well as it hauled. We watched as the FJ, in full race trim, competently conquered the creepy-crawly sections in Low range and flew over the faster sections in 4-Hi. What made the FJ work so well in so many different situations on the trail? It wasn't the beautifully crafted 4130 chrome-moly rollcage. It was the finely tuned long-travel suspension.
"Racing improves the breed" is a clich, but it's based in reality. Pounding over rough terrain at warp speed tends to bring out the best, and the worst, in suspension design. Products that hold up get developed and brought to market. Stuff that doesn't cut it gets dismissed.
This time, we'll delve into shock types, shock mounting strategies, and shock protection. Shock protection? Yes - in the form of bumpstops and limit straps.
If you happen to see Donahoe's FJ Cruiser on the trail, rest assured that the driver didn't take a wrong turn and stray from the racecourse. It may have been bred for high-speed desert competition, but on the trail it's still right in its element.
Here's an X-ray view inside a shock. The shock rod connects to a piston assembly. The piston moves up and down inside an oil-filled chamber. Above the oil chamber is a nitrogen-charged chamber that's separated from the oil chamber by a floating piston (aka dividing piston). The purpose of the dividing piston and the nitrogen chamber is to keep the oil from foaming as it heats up during hard use. The size of the nitrogen chamber varies with the temperature of the shock oil below. Hot shock oil expands. This in turn pushes on the dividing piston and shrinks the nitrogen-filled chamber. If the shock oil were allowed to turn to foam, the shock would be rendered ineffective. A shock piston moves through oil in a controlled manner. A shock piston moves through foam much too easily and with no control. | 
Here's a shock piston assembly up close. The piston has holes (aka ports) through which the oil flows. Between the piston and the locknut is a stack of spring-steel washers (aka shims). These shims are arranged according to their diameter and thickness. The shims are designed to deflect and regulate the flow of the oil through the ports. We'll delve further into shock internals and tuning another time. | 
This is the bottom of the shock food chain: a basic, small-diameter OEM shock. It doesn't hold much oil and readily heats up and loses effectiveness - also called fading. Even though OEM shocks fade easily, they are still way better than nothing. |