It's actually a bit deceptive to refer to a shock like VariSshocks's QuickSet 1 as a single-adjustable shock. It is single-adjustable in that there is one knob to turn through 16 clicks of adjustment. On the other hand, each click adjusts both rebound damping (the shock coming apart) and compression damping (the shock coming together) at the same time. "It's just the way the ports are inside the shocks," explains Alston. "The oil flows both ways through one adjuster." Some single-adjustable shocks, Alston went on, adjust only one half the equation-either rebound damping or compression damping, but not both. "Ours adjust both together-both get stiffer, and you can adjust both ends. If you take a look at the accompanying Single-Adjustable VariShock dyno chart, this is clearly illustrated. As rebound damping (pulling apart) gets stiff, so does the compression damping (coming together). The compression damping doesn't get as stiff as the rebound damping, but it does go up in proportion to the latter, making the whole shock stiffer or softer. "They're actually a phenomenally cool tool to adjust a car's suspension, and the fact that you can adjust it at all means you get closer to where you need to be," Alston declared, "but it's better if you can adjust both sides."
On the other hand, double-adjustable shocks like VariShocks QuickSet 2 route the shock's internal oil through both adjusters. When it comes to how the oil flows, it's a completely different pathway-the valving is way more complex, and that complexity, along with the adjustability it permits, is what you're paying for when you step up to double-adjustable shocks. "The lines are completely independent," said Alston. "That's why you can have full stiff on one setting and full soft on the other setting." The range of adjustment is also much more vast. Instead of the QuickSet 1's 16 adjustments, the QuickSet 2 provides an amazing 256 adjustment combinations. Because both types of damping can be adjusted separately, the range is exponentially greater than that found in a single-adjustable shock. Again, look at the QuickSet 2 shock dyno chart and see how great the range of settings is-from very soft, as in less than 100 pounds of force, all the way up to 500 pounds of force and everything in between.
These settings-rebound damping and compression damping-operate separately in the car. You might think the two are related, but in fact they actually don't have anything to do with each other. "The most obscene example of this is a drag race car," Alston continued, "and the most extreme is the front of the car." For instance, at launch, the shock needs to come apart as fast as possible for maximum weight transfer, but not so fast that when it runs out of travel, it shocks the chassis hard enough to unload the tires and unhook the car. "Much more misunderstood is when the car comes down and hits bottom," says Alston. "Also, the tire can unload if the front end settles down too quickly and hits the bumpstop, resulting in that bobble many racers experience at the gear change. "I've worked on cars that picked up a couple of tenths from front shock tuning" Alston says. "When it comes to drag shocks, "People think the softer the better, but they're wrong."
On the other hand, the benefits of adjustability aren't only for those who burn up the straight line. "Drag racers don't have the extreme loads caused by turning," Alston began. "On the other hand, those who go in for turn-oriented events like autocross don't have the extreme acceleration loads to deal with. The goal there is to determine how to transfer weight from side to side.... you don't want to transfer more weight than the car can use." Again, being able to separately adjust rebound and compression damping is a valuable tool to achieving this. "Not being able to adjust them separately," Alston said, "is like adjusting timing and jets together. It's great if you actually need more or less of both at the same time, but not so much if they need different settings." Again, the settings are independent, and you have more range. "They're much more sophisticated," Alston summed up, "and they're one of the easiest things to adjust on a race car.
A Word About Springs
Ostensibly, this article is about single- versus double-adjustable shock absorbers. On the other hand, it would be remiss of us to write an article about selecting shock absorbers without at least briefly discussing springs. Given all the variables involved, you're not going to be able to truly optimize your suspension unless you can dial in shock valving and spring rate. Alston puts it more bluntly: "The biggest problem with shocks is the wrong spring."