Youth ATV suspension upgrade: Phase II

Jun. 01, 2004 By George Szappanos

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Stage I involved widening the machine to make it more stable. This month we take the plunge into mini-quad shock upgrades. This stage of the upgrade series can be most expensive, but fortuitously, offers the most noticeable improvement over a stock machine. The article below will attempt to shed some light on what makes the difference between a stock shock and a set of performance shocks, and provides some insight into why mini owners ought to seriously consider them.

Stock vs Performance When it comes to a mini-quad suspension, the manufacturers not only have to design a shock to handle the worst case scenarios such as really heavy riders hitting really hard jumps, but they need to do it in a cost effective manner. And the needs of most recreational riders are quite different than a racer or aggressive trail rider. The reality is that very few youth ATVs (maybe less than 10%) will ever be used in competition. Why inflate the cost of the machine by another five hundred dollars to satisfy the needs of the minority purchaser?

A comparison of stock Kasea front shock (top) and Works front shocks.

So the OEMs have developed decent shocks that offer reasonable compliance over the most drastic conditions. They do this by providing a very stiff shock spring and very little (if any) damping. This translates into a very rough ride for most mini riders and very little useable wheel travel. For young recreational riders and racers this means landing jumps with a hard thud which can fatigue the rider or cause a lack of control, but also stresses the suspension and chassis- sometimes to the point of failure. This shortcoming was not lost on the suspension aftermarket community. Companies such as Works Performance have developed shock absorbers to directly replace the stock "toy" shocks. Based on a rider's weight, riding style/level, and ATV configuration they will build a custom set of shocks to offer dramatically improved performance over stock. The shocks are uniquely built with customized valving and a spring rate that maximize the available travel of the suspension for a given rider.

How Shock Absorbers Work The role of the ATV shock absorber is two-fold: to support the weight of the ATV in a resilient manner, and to dampen the motion of the wheel. The first part is relatively easy- that's what the spring is for. The second part is usually what's absent on stock shocks and where all the technology and sophistication lies.

Figure 1. courtesy Work Performance

When the shock is not moving the pressure on each side of the piston is the same. The check ball acts as a valve sealing the piston. Behind each ball (there are three) are springs which are all different- going from light to stiff. The stiffness of the spring determines how much pressure will have to be created to open the valve.

Damping is the shocks ability to slow the motion of the shock extension or compression and is needed for a few reasons. Consider an ATV coming off a serious jump. Without damping the spring would need to be sprung more heavily since the only thing resisting bottoming of the suspension is the spring force. On smaller jumps, the same undamped suspension will seem unduly stiff and uncompliant. Additionally, the shock controls the wheel motion over rough terrain and jumps in an effort to maintain contact with the ground. Damping of shock absorbers is achieved by forcing oil from one side of the shock absorber piston to the other. The size of the passage controls how quickly the oil can pass and therefore controls the speed of the piston for a given load (pressure). As the suspension compresses, oil is pushed from the top of the shock past the piston into the bottom part of the shock. As the suspension rebounds the oil is pushed back up into the top of the shock.

Figure 2. courtesy Work Performance

When the quad hits a bump, the shock shaft starts to move through the oil. This causes pressure on the front side of the piston. How fast the shaft moves determines how much pressure there is. If the piston is moving slowly, then only one ball compresses its spring and allows oil to flow around it. If the piston moves quickly (higher pressure) then more than one ball will open allowing more oil to the other side of the piston.

There are two types of damping- compression damping and rebound damping. Compression damping occurs while landing jumps and hitting bumps. Too little compression damping and the shock will bottom out; too much and the shock will seem harsh. On Works shocks compression damping is handled by four-stage valving, which means very simply that the flow through the passages is controlled in a way that provides a nearly linear relationship between shock velocity and damping, thus avoiding overdamping during really hard jolts. Rebound damping is two-stage and controls how quickly the shock will move back down after being compressed. Too much rebound damping and the shock can "pack" on tight whoops (the shock can't extend enough before the next hit), and too little might allow the back end to kick up as the ATV leaves jumps.

Proof is in the Puddin' Installation of the shocks is dead simple- in our Kasea Skyhawk project machine they were a drop-in, direct replacement. Works Performance was provided with the particulars of the intended machine which in our case meant informing them that we had +2 A-arms, stock tires/wheels, and a stock swingarm. This info is critical in calculating the leverage ratios between wheels and springs. Should this data ever change (or rider details), Works can revalve the shocks to compensate. After installation, the difference was immediately noticed by simply doing the "garage test" of bouncing on the pegs; the quad moved up and down easily with much more effective travel. Picking up the rear end of the machine and dropping it from a distance of a couple feet returned a buttery "pooof". Even at this point, the new shocks seemed night and day different than the stockers. But a testimonial from the machine's young pilot would be the final word, so off we went to the track with "Zack-man", our 7 year-old test rider at the controls. After a few laps of the AMA motocross track, we quizzed the speechless Zack-man on the virtues of the new suspension: Kids Korner: So, Zack, what do you think of the new shocks?
Zack-man: "...uhh,... well, ... they were great."
Translation: The Works shocks worked beautifully. With the added suspension travel and compliance they made me more confident over jumps, and actually improved my lap times.

Zackman taking the re-sprung Kasea through the rhythm section.

Kids Korner: "Do you think it was an improvement over the stock shocks?"
Zack-man: "yah. totally"
Translation: The two are not even in the same category. When I used to come down on jumps it was brutal, sometimes coming down so hard I'd nearly bash my helmet in the bars, and then nearly crash as I try to recover. The Works shocks are like a breath of fresh air. Kids Korner: "Any remaining comments?"
Zack-man: "uhmm..."
Translation: The Works shocks are quality pieces- machined billet aluminum ends, nitrogen charged, oil-emulsion shocks that are likely to suck up all the punishment I intend to serve them! Zack-man: "Can I have some ice cream now?" >>>> Next Month- The finishing touches such as steering dampers, chain tensioners, and extended swingarms.

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