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RMK goes on a major diet - drops 40 lbs.By Stephen W ClarkPOLARIS' purpose-built mountain sled, the RMK, has been among the leading mountain machines since its introduction in 1997, selling more than 150,000 units in that time. So when Polaris' engineers redesigned it for 2011 they were trying to fix something that wasn't necessarily broken. But they were extremely weight conscious.
The result? They are stepping up their game considerably using a chassis loosely based on the Rush along with a host of weight-saving changes engineers tell us cut 40 lbs., bringing RMK down to 431 lbs.
Weight is a huge factor in how well a mountain snowmobile works and with the new 800 PRO-RMK, Polaris will be extremely close to having the lightest 800 mountain sled.
The entire RMK lineup has been changed for 2011 and one of things to go is the Dragon name, the premium machines now carry the PRO-RMK designation and the base model remains simply RMK. The Assault also returns in two forms one an RMK with a 155-inch track, the other a crossover Switchback Assault (see p. 20). For the time being the 600 RMKs remain in the IQ chassis.
The weight loss
Where did Polaris come up with all the weight savings and what's different on the RMKs?
First, the chassis is considerably different and uses a structurally bonded (glued) aluminum chassis with a two-piece cast bulkhead, like Rush. Polaris claims that not only is the new chassis lighter but 300% stiffer than before. The 800 Cleanfire engine is roughly the same, aside from some minor tweaks and mapping changes.
The rear suspension is lighter because the torsion springs have been removed. However, some weight has been added as Polaris has ditched the air shocks and gone back to coil-over spring shocks. Polaris says this change is for better bump control and balance. The rest of the weight has been shaved with a bunch of small reductions, for example the running board rail that was steel is now aluminum, the rear bumper is made from carbon fiber and the seat support is aluminum. More weight was removed via new narrower tunnel cooling extrusions.
Polaris also has created a purpose-built RMK brake system with Cyclone master cylinder and lightweight single-piston caliper too.
While there are plenty of changes, many of the proven RMK parts from the IQ-based model, such as its track, engine and skis, remain for 2011.
Polaris tells us part of the design criteria for this model was to lighten it while retaining the good balance and handling that the IQ RMK had become known for.
Our initial impressions from riding the new RMK for several hours in Utah is that the machine climbs and moves through snow much better than before, and despite few engine changes the machine feels a lot more powerful. (probably due to a better power-to-weight ratio.) While we love the weight and climbing ability of the new RMK, after our initial ride we were not totally sold on its handling. The new riding position can feel like a REV-XP and, at times, hard to control, especially on the PRO-RMK with its tall, wide Pro-Taper handlebars.
Our handling concerns could be due to bad snow conditions though or individual sled setup on the prototype machines we rode. One thing we know for sure is that when it comes time to ride the 2011 machines from all the manufacturers later this spring, the RMK will be one of our top priorities.