October 6, 2004

Suspension Tech Part II



Components and complete systems

Snowmobile factories have done an excellent job advancing suspension technology in the last decade. Polaris, Arctic Cat, Ski-Doo and Yamaha have used long-travel suspensions with high-performance shocks to improve our weekend outings and reduce our Monday aches.

One of the newest and most advanced factory rear suspensions is the Mono Shock RA, found beneath 2005 Yamaha RX-1.

Yamaha dropped the two-shock ProAction and designed an all-new, single coil-over shock-based skid loaded with features.

First off, a 46mm aluminum high-pressure gas shock controls all dampening for the rear suspension. There are three preload settings, selected by adjusting the preload cam at the rear end of the spring. The step-style cam itself sits on another cam that is moveable through three different positions, 10mm apart, for a 30mm range of movement.

An external "remote" compression clicker dial allows the rider to adjust compression dampening easily, without reaching under the sled. The remote clicker is mounted in the right side of the tunnel, just beneath the seat. This means you can adjust the ride comfort while you ride. When you come upon a rough section (we tried this out multiple times), reach down and turn the large, glove-friendly knob counter-clockwise. When you drop back onto a smooth trail, turn it back clockwise for a smooth, comfy ride. Stop sacrificing comfort in several areas because your suspension is set up for a single condition.

Another impressive aspect to the Mono Shock skid is the weight reduction. Compared to the ProAction it replaces, the Mono Shock is a featherweight.

 

Long Version

Mountain sled suspensions have evolved into their own breed of skid frames. Although they are different in their individual characteristics, Ski-Doo’s SC-10 III, Polaris’ IQ RMK, Arctic Cat’s FasTrack and Yamaha’s all-new ProMountain share the same basic design. All run a front rail shock wrapped with a coil spring. The rear shock connects to the slide rails and the rear scissor arm. Two wound preload springs (some manufacturers use round wire for their springs; other use square wire) wrap around the rear shaft and ride on blocks mounted on the slide rails.

The two-arm, preload spring suspension style doesn’t offer the maximum in adjustability and tunability, but the design is relatively light and functional. Generally, the front shock features a cam adjuster for spring preload tension adjustment. Performance-equipped models often have compression adjustment clickers.

The rear preload coils have either three- or four-position cam adjuster blocks, so the rider can adjust preload, or ride-height.

All OEM styles have some sort of rear arm stop, whether it is a control rod like Yamaha or a simple stop shaft like Arctic Cat.

These three areas, front shock/front arm, rear shock/springs/rear arm and the rear stop, are what make a rear suspension work. Each affect the way the rear suspension transfers weight, controls traction and allows the track to get on top of the snow (or trench through it).

So it should come as no surprise that this is where aftermarket companies focus their attention. You’ll rarely see someone change out slide rails for aftermarket ones. There’s no room for improvement there. But arms, scissors, shocks, springs, rods and hardware fill hundreds of catalog pages.

Fabcraft offers everything from replacement arms to complete suspension systems, like its mountain suspension. Mountain Performance, Mountain Machines, Holz Racing Products, Starting Line Products, Cutler’s Performance Center, Mountain Addiction and other aftermarket companies offer components that improve suspension performance, reduce weight and catch stares.

The Holz Racing coil-over kit, for example, removes 5 lbs. of rear suspension weight on a 2004 Polaris RMK. It also adds two inches of vertical suspension travel. The coil-over kit replaces the two wire preload springs on the rear shock with a coil spring on a high-performance gas shock. The changes in springs, preload adjusters and shocks allow the user to tune the suspension to a finer level than before.

 

Front Suspension

The front suspensions have made an even more dramatic change in recent years. A few years ago, three out of four OEMs used some form of a trailing arm suspension. Arctic Cat was the lone pioneer in the A-arm field. Now, with Polaris’ introduction of the IQ chassis, all four manufacturers have a type of control or A-arm front end.

The new suspension styles are improvements on the old designs, but still give the aftermarket room to work.

Stock components, like control arms, trailing arms, spindles and radius rods, are all designed for one thing—durability. That usually comes at a cost to weight.

But aftermarket arms and other components curb the weight. Lightweight control arms from Mountain Performance drop 7 lbs. off the nose of a Ski-Doo Summit Rev. MPI can get 13 lbs. off of a trailing-arm equipped Summit or Yamaha. Components such as these are made from high-quality metals like heat-treated 4130 chromoly, billet aluminum or carbon fiber.

Then there’s titanium. Diamond S fabricates all sorts of titanium suspension components for snowmobiles. In fact, Diamond S makes an entire chassis out of titanium. Trailing arms made from the high-tech alloy weigh less than 2 lbs., so it’s easy to see how easy it is to take weight off.

But, keep in mind, these components aren’t always cheap. If you’re setting out to lighten up you stock sled and make it handle better, make a plan and a budget to work with. That way, you don’t run out of money before you’ve finished your sled.

And, if you’re on a real tight budget, there are some less-expensive parts that still save a few pounds.

 







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