The Summit X, like other Ski-Doos has a high performance ROTAX engine, along with a new Super-V track with 1.75 inch lugs which hope to take the world by storm!!! The RMK has the new Gen II style hood, along with 1.75 inch lugs and the new Polaris engine. The well known XTRA-10 rear suspension allows any rider have the most comfortable ride offered in the Mountain class of sleds. With all these battles, it should be an exciting season, no matter which stone you decide to overturn!