HOW-TO: Tune your suspension
Every ATV currently being sold by a reputable manufacturer has shock absorbers. It’s how they isolate rough terrain from the rider, and it’s perhaps the most important part of your ATV besides the engine. Shock tuning can make or break a machine, as it controls comfort, handling characteristics, safety in rough terrain, and how enjoyable your ATV is to ride. We have been working with shocks since day one, and we can never leave the settings alone. Why would manufacturers offer adjustable shocks if they didn’t intend for you to play with the settings?
Here’s the bad news. While you’re clicking away at compression or rebound, or tightening up or loosening preload, you may actually be doing more harm than good. All machines are tested before they are introduced into the market to convey the manufacturer’s best recommended settings for a wide range of riders. If you get lucky enough to fall into the slotted category the suspension was tuned for (rider weight, terrain and riding skill), you may never have to adjust your shocks at all. But what if they just don’t feel right? Suspension tuning can always be made better than stock—that’s a proven fact. Otherwise, we wouldn’t have aftermarket shock companies like Fox, Elka, Race Tech, Works Performance, NoLeen, iShock, Progressive and many more providing aftermarket componentry to increase the comfort and handling prowess of your machine. But just what do shocks do?
HOW A SHOCK WORKS
We headed down to Race Tech’s headquarters in Corona, California, for an in-depth shock seminar, for which you can sign up for yourself by calling Race Tech at (951) 279-6655. We met up with the gurus at RT for a little schooling and to help illustrate just what happens when you turn that adjuster. So here are the basics.
Shocks are made up of two parts, and they work very differently. The first is the spring. While you may know what a spring is and know about its basic functions, it’s a complex art that requires brains and skills to make it work properly. Steel springs are wound from spring steel (go figure), a material that has memory, which means it wants to return to its original shape when deformed.
Spring rate, or stiffness, is determined by how much force it takes to displace a spring in a measured distance. So if you have a spring rated at 100 pounds/inch, it takes 100 pounds to compress the spring 1 inch. That being said, it takes 200 pounds to compress it 2 inches, 300 pounds to compress it 3 inches, and so forth. This is called “spring rate.” This is with a straight-rate spring; progressive and dual/triple-rate springs differ vastly.
If you stack two shorter 100-pound/inch springs on top of each other, the initial rate will be much softer than 100 pounds/inch, until one spring compresses completely and acts as a solid. Then, the secondary spring retains its true 100-pound/inch rate. This is how manufacturers can get a softer initial ride from progressive or multi-rate springs while retaining bottoming resistance further down in the stroke.
The second part is damping. Unlike springs, damping is usually unrelated to the shock’s stroke position. Springs exhibit more force deeper down in the travel, while damping is only affected by the velocity of the shaft movement. Damping is viscous friction, which turns kinetic energy into heat. When the wheel contacts a bump, the spring is already pushing against it, but the valving is stationary. As it contacts the bump, the suspension moves through its stroke, forcing shock fluid through the shock piston. This is how you control compression and rebound stiffness.
By making the holes that the fluid passes through smaller, and therefore flowing fluid at a slower rate, the shock becomes “stiffer.” Opening up these ports and allowing the fluid to pass through more quickly, it “softens” the suspension. Think of it this way: the spring controls the ride height and stiffness, but the damping controls how quickly the suspension can move through its range of motion. This is where we get the adjustments from.
WHAT THE CLICKERS DO
For the purpose of this story, we used a Race Tech G3-S shock, which is a high-end piggyback unit offering full adjustability. It consists of a body, which is where the shock shaft and piston travel, and displaces fluid; a reservoir, which holds the shock oil that the shock shaft displaces; and the spring, which controls ride height and vehicle weight.
In the shock, between the reservoir and the body, there are ports that the oil must flow through when the shock is compressed. Base valving is set up using shim stacks around the piston or valve. The valve has ports that direct oil flow around the shim stack, which can be custom-tuned using large spring-steel washers that vary in strength depending on their diameter.
The smallest valve shim is called the “crimp,” and it is the shim which all the other shims bend around when the shock is compressed. Valving is complicated; we could talk for hours about tuning valving and what different shims do, so we will keep it simple. By adding more large shims to block off the valve’s ports, you can make the base valving much stiffer. This works by making the space the oil has to move through much smaller, slowing down the stroke.
The compression adjusters work in unison with the valving, as not all the oil passes by the valve when the shock is compressed. The G3-S shock we used for our demonstration has two adjusters for compression: high speed and low speed. The high-speed adjuster is used for quick hits, like jump landings, G-outs and big holes/whoops. The high-speed compression adjuster is a large port with a preloaded spring inside and is attached to a beveled stop at the end of the port. When the shock is compressed with a lot of force quickly, the oil forces the stop out of the way, compressing the small spring and allowing the oil to be pushed into the reservoir. The tighter you make the high-speed adjuster by turning it inward, the more spring tension is placed on the stop, requiring more force to move it out of the way to bypass the oil.
On the low-speed side, the port is much smaller, and flow is controlled by a tapered needle that is inserted into a hole at the end of the port. When the needle is backed away from the port, more fluid can flow into the reservoir at low shock speeds, potentially bypassing the valve stack.
Low-speed controls body roll and slow elevation changes, like shallow, rolling G-outs. Tightening up low-speed compression will reduce the machine’s tendency to dive and squat under acceleration and braking by slowing shock-shaft movement.
Rebound works very much like compression, but it limits the shock’s speed when it extends after being compressed. With no rebound damping, the shock would extend very quickly, causing a bucking motion because the spring’s energy is not controlled. Rebound clickers are on the bottom of the shock shaft, as the oil bypass for the rebound adjuster is located on the shaft itself. It moves through ports below the valve stack and comes out the top of the shaft and above the valve stack.
Rebound adjusters use a needle-port design, like low-speed compression, but also allow some backflow—unless a check valve is used. What this means is that tightening up (stiffening) your rebound damping will also stiffen your low-speed compression on most shocks slightly, as the oil can pass through the rebound circuit while being compressed. Most shocks don’t have a check valve for independent rebound, but some high-end racing applications can be ordered with one.
Your spring’s stiffness and preload affect the ride and ride height. There are many options available for springs. You can use a single-rate spring that is preloaded, a zero-preload setup that uses a small “top-out” spring just to keep the springs in place when the shock is fully extended, a progressive-wound single spring that changes rate depending on its position, dual-rate springs that offer different stages of stiffness during the stroke, or even triple- or quad-rated springs. Multi-rate spring setups are used to control stiffness during different parts of the stroke using crossovers, which are solid pieces of material that change when the springs come into effect in the shock’s stroke. Again, for simplicity, we will use single-rate springs for our examples.
Preload is the measure of how much tension is placed on the spring when the shock is fully extended. More preload will cause the machine to sit higher in its travel, increasing ride height and ground clearance. Preload can also make the ride stiffer by causing the spring to require more initial force to be compressed. Increasing preload will keep the shock up in its stroke, allowing more shaft movement to slow down wheel movement when you hit an obstacle. If the spring preload is too soft, the suspension will sit down in its stroke and not have enough up-travel to absorb bumps correctly. If it is too hard, it will not allow the valving to do its job properly and exhibit bouncy, jarring behavior.
Spring preload should be adjusted to suit the proper amount of static sag for your body weight, or how much the shocks compress when you sit on the machine when it is sitting still. As a general rule, your static sag should be in the ballpark of 1/3 of the suspension’s total wheel travel, meaning if your machine has 9 inches of total travel, it should have 6 inches remaining at static ride height to absorb bumps. This is called up-travel. Down-travel, or droop, is how much wheel travel is being compressed, so if the ground suddenly dropped out, the wheels would drop 3 inches before the shock was fully extended. There is no perfect number. Everyone’s preferences differ, so the 1/3 mark is a good ballpark to start with.
Let’s say you own a sport quad and have never messed with the suspension. Or, maybe you just bought a new machine and want to set it up for your weight and skill. Your first move is to measure the sag and adjust your preload. As a rule of thumb, we will use the 1/3 mark as explained above. Say you’re working with a single-rate spring; you want your ballpark preload measurement to be between 6mm and 10mm for optimal ride quality. If your spring needs more than 15mm of preload to achieve the desired sag amount, you may need to switch to a stiffer spring. Too soft of a spring will allow the suspension to move too quickly, inducing dive, squat, and body roll, as well as poor bottoming resistance. If you need less than 1mm–2mm of preload, you may want to go down in spring rate, as the ride will be harsh and the suspension will not move through its stroke optimally.
Next, you go to compression damping. For softer terrain, you will want to increase the shock’s compression stiffness, which will reduce weight transfer and aid in traction and vehicle control by controlling pitch and yaw. For hardpack, loosen up the rebound adjustment to allow the wheels to stay in constant contact with the ground; this will increase traction. The easiest way to dial in your valving adjustment is by having a friend watch you ride through a rough section and watch how compressed the suspension is while you’re riding. If it is too low in the travel, the rider may think the shocks are too stiff and back out the compression, when in reality it’s near the end of its stroke and is harsh because it’s too soft. Adjusting your suspension isn’t a quick one-two thing; it takes time and effort, and the rewards are great in the end.
Adjusting your suspension can be tedious, but it isn’t difficult. It’s all a matter of mathematics. There is weight being controlled by spring and damping forces. More weight—be it on the vehicle or the rider itself—will demand a stiffer spring and damping force. This is where aftermarket shock companies like Race Tech come into play. Race Tech offers valve and spring kits for most popular applications, and if they don’t offer kits to build your stock hardware for cheap, they can certainly supply you with a set of their custom-series shocks for a little more coin. Rebuild and valving kits are available from Race Tech for great prices, and their website (www.racetech.com) has many how-to articles and charts to help you determine the right parts you need to make your ride optimal. Give them a call at (951) 279-6655 and tell them Dirt Wheels sent you, or pick up your own copy of Race Tech’s Motorcycle Suspension Bible, the ultimate how-to book that explains every aspect of suspension tech and tuning you could possibly imagine, including detailed pictorials of how to rebuild your own shocks! The book is available through Race Tech or online at sites like Amazon.com, so get out there and get tuning!