Arctic Cat’s unusual floating front arm on the 2005 Sno-Pro racer turned what was otherwise a very poor cornering sled into a very capable railer. Cat’s 128 x 13.5 wide track has had a reputation for being resistant to turning because of its extra length. This length generates excessive side grip, undermining the skis’ ability to lever the sled in turns.
Last season the the Cat crew introduced a radical yet simple piece of engineering allowing the front arm’s upper mounting pivots (inside the tunnel – just behind the drive sprockets) to “float” back and forth more than an inch. When this innovation was unveiled as a handling enhancer, its unique benefits were not fully explained to the press or even to racers.
To make the floating front arm work, the rear arm drop link had to be converted to a fully coupled (rear-to-front) unit using conventional coupling blocks like AC’s trail sleds use. The difference is in how early the coupling moment hits on the Sno-Pro set-up versus the trail sleds.
Here’s what happens. When you squeeze the loud handle on a conventional snow bullet, the sled is driven forward by the tracks rotational forces coming through the front arm and into the tunnel near the footrests. The sled is not driven forward by the rear arm. It’s drop link design compensates for the geometric arc of the front arm to maintain consistent track tension.
All snowmobiles, when turned by the front skis, are pivoting precisely at the front arm of the skidframe. In the case of AC’s longer 128 inch track, there’s a ton of sled that has to be pried around behind the driver.
With AC’s floating front arm, the track and skid actually drive forward in the chassis until the rear coupler blocks lock up at the rear arm before the floating front arm hits its forward limit. This causes the Sno-Pro to “think” it’s pivoting at the rear arm were the power is now entering the chassis (when the coupler blocks contact the drop link). This occurs a considerable distance back from the front arm and provides more leverage to swing the rear of the sled around in tight turns.
This may take more than just one read to understand but as far as we’re concerned, it’s engineering genius.
(Originally published in Supertrax – Volume 17, Number 1)