A snowmobile has an air intake system integrated into the snowmobile body, and with air intake vents facing rearwardly towards the rider. The air intake system includes a plenum defined by a portion of the body and ducting extending within the body. The ducting is porous to allow the air input noise to be dissipated within the engine compartment. The snowmobile further comprises couplings which may be realigned to accommodate wear. A frame coupler allows multiple differently configured frame tubes to be connected to the tunnel. The chassis of the snowmobile includes a casing for receiving the gears which drive the belt.