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There is no way around it, when you first look at the new Polaris Rush; your eyes are automatically drawn to the new rear suspension's external linkage.
The sled's whole rear tunnel is totally different than anything you have seen on a snowmobile before. A large triangulated tube section hangs out the back, linked to the suspension rail on the bottom, pivoting around the tunnel in the middle and activating a large mono-shock on top.
It screams radical, but also strongly hints at new possibilities in the ongoing search for improved suspension performance. If the design proves successful, it will set a new standard on how a snowmobile should look, just like Yamaha's mono-shock suspension did to motocross motorcycles back in the 1970s.
Polaris' big ideaBy moving the suspension arms outside of the track, Polaris engineers gained a larger freedom in designing the linkage and selecting the most efficient shock, compared to the limitations automatically imposed when you try to stuff everything inside the track envelope. You would think you're looking at a longer travel suspension, but that's not so.
The Rush's rear suspension travel is about the same as an IQ Dragon's, but the new layout offers better travel management, especially when it comes to bottoming out on large moguls. There is nothing quite as discomforting as hitting a large mogul a little too fast, and suffering the spine jarring jolt when your suspension bottoms out. With the limits of designing inside the track envelope, the engineers felt they could not get the correct lever geometry, instead having to resort to progressive springs and harder compression dampening to obtain any resemblance to a progressive rate.
In theory, a progressive rate would allow you a softer ride over small bumps and a stiffer spring when the suspension reached the end of its travel. When this approach was tried on earlier snocross racers it resulted in a strong "kickback" when the spring released again. That made for a wilder, bucking ride. By using straight rate springs and letting the geometry of the linkage multiply the spring's travel at the end of the stroke, there is a longer distance of both shock and spring travel to manage the last few inches of suspension movement. As a result the G-out forces are controlled better when approaching the crucial point where a normal suspension would go solid.
Sounds great in theory you say, but we have heard these claims before, and they did not all pan out, which is why our test crew was eager to spend some time on the new sled during new sled testing in Colorado last March.
Senior Editor Mark Boncher had the most time on the sled as he rode it at its introduction in Utah, and also spent some extra time playing with the adjustments to tailor it to his size and riding style. Everyone agreed that the new suspension performed great on large moguls and it did not give you a spine tingling jolt even in the largest G-out conditions. The expected kickback also was controlled and not a large problem.
In stutter bumps and medium-sized moguls, our test riders felt the performance was about the same as a regular Dragon suspension. Boncher, again who had spent more time on the set-up, was the lone rider to claim he achieved relatively good performance all the way through the suspension's travel.
The new Rush suspension is particularly sensitive to the correct set-up, the Polaris engineers explain, and that's why it comes with a set-up gauge that shows you the correct location of the spring pretension collar on the shock to match your weight. The stock spring has a 180 lbs./in. rate, and is expected to best cover rider weights from roughly 150 to 230 lbs. This is definitely much to ask from one spring, and adjusting it with pretension and shock settings over that large of a range will obviously end up with some unwanted compromises.
That's why Polaris will offer two additional springs by the time the Rush reaches the showroom floors. There will be a softer spring with a 120 lbs./in. rate, and a stiffer spring with a 250 lbs./in. rate. To obtain maximum performance in your weight category, it may be a good investment to buy the 250 spring if you're a large rider, or the 120 spring if you are a lightweight rider or smaller woman.
Polaris has come a long way in the shock department working with Walker Evans units. Walker Evans gained its expertise in rough off-road truck racing, a technology that matches well with big bump snowmobile performance. Polaris uses the Walker Evans advanced needle controlled shocks both at the rear suspension and on the front ski suspension. The needle control adds another dimension of tuning as the shock piston travels up its stroke, just as a needle in a carburetor slide controls the mixture relative to throttle opening.
The shock action also is progressively load-sensing, and the compression dampening is adjustable within 14 optional settings. There is no adjustment of rebound dampening. The engineers felt that previous experience with too many adjustment variables more often got the consumer lost, so Polaris spent a lot of time getting the rebound to work correctly to prevent too strong a kickback to potentially losing that advantage to incorrect adjustments.
The big surpriseThis new suspension delivers on big bump G-out performance, as was the promise, so what's the great surprise?
Testers all came back with rave reviews on the Rush's handling. "This is the best handling snowmobile Polaris has ever made" was the general consensus. It carves corners as on rails, and reacts very positively to body movements. There is negligible body roll and you can power through corners with the inside ski barely lifting off the snow.
Power transfer also is good, there is no excessive ski lift on hard acceleration and cornering is positive. Want more turning action on the front? Just move forward a little and the sled responds. Where did this new-found handling come from? It's actually the result of a number of chassis and front suspension improvements.
Aside from the rear suspension linkage transferring power and weight better, the chassis is a much stronger design thanks to its tube frame structure. The chassis also is 60% stiffer in torsion, which means it twists less when cornering and lets the shocks do their work. Any criticism of body twists is now in the past.
Polaris chassis engineers spent a lot of attention on the design of the sway bar. They felt earlier designs used too much travel before becoming effective, allowing the body to roll too much before the action could be corrected. Once a chassis starts rolling the action actually increases and it's harder to correct roll the further it progresses.
The new linkage ratio arrests the roll much earlier, resulting in improved front end behavior and better handling. One of the engineers' goals was to make the new long-travel front ski suspension handle as well as the early triple Indy chassis. Needle controlled Walker Evans high-pressure adjustable shocks also reside in the front suspension, complementing the action of the rear suspension and producing a well balanced handling package.
Another standout feature is the front heat exchanger. It looks like a radiator in a precarious position in the pan's front, but is in reality a strong aluminum extrusion heat exchanger that can take abuse from rocks and ice chunks without failing.
In the clutching department, the new P2 secondary is said to be an improvement over the stiffer compression-spring-only TEAM clutch. The new P2 clutch comes with provisions to install a torsion spring for those who prefer quick backshifts, and optional torsion springs will be available.
With so much attention on the new mono-shock rear suspension, you might think that this sled is aimed only at serious bump riders. Polaris reassured us that it is also aimed at the regular trail rider. Our test crew seemed to agree; this is the best handling Polaris ever. Buy it for the great on-trail handling performance, and get the big bump G-out insurance as a bonus!