AmSnow.com is now SnoWest.com
What does this have to do with snowmobiles?
Our Evinrude team devised a mogul test course on Fox Lake and brought a number of sandbags to experiment with weight distribution. First we placed a 40-lb. sandbag on the back of the tunnel, but this had little effect on the ride. Next we moved the bag to the center of the sled, in fact increasing the mass centralization, but this made the ride worse. Finally we strapped the 40-lb. sandbag to the front bumper and the ride improved dramatically.
The front-end no longer jumped around because the extra mass and increased inertia forced the leaf springs to bend and soak up bumps. On Evinrude’s Bobcat the engine was located in the center, while the Arctic Cat Panther mounted its engine up front, both lower and closer to the skis.
Our conclusion was that the secret to a better ride was not so much the slide-rail suspension as everyone suspected, but actually mounting the engine further forward, which de-centralized the mass and increased the vehicle’s inertia and improved its ability to soak up bumps.
Everyone involved with vehicle design at that time quickly realized the advantage of a front-mounted engine, whether they understood the dynamics behind it or not, and by the early 1970s all sleds had their engine up front and their own version of a slide-rail suspension.
With all this research and work preformed 40 years ago, why would we all of a sudden try to get back to mass-centralization that gave us such a bad ride?
First, it could be a new breed of young engineers that lack a historical background in the industry, their brains full of Formula One car racing-based computer programs. In Formula One mass-centralization is an advantage as the decreased inertia makes the car switch direction in the horizontal plan much quicker in the corners. Obviously bump performance is of no interest as F1 racers run on glass-smooth surfaces.
Snowmobile trails are much different, you need bump control. So why do some manufactures still insist on moving engines back in the chassis? One reason is weight. Some 4-stroke models are so heavy that there is too much weight over the skis, which makes them hard to turn.
In such a case the skis still have enough mass above them to work against the springs even with the engine moved back. The problem comes when designers get confused by the buzz words and go on a weight saving program together with a mass-centralization program.
On very light sleds it is important to keep the little weight you have moved out front to increase inertia and improve bump performance. That is why some snocross models that did not go for mass-centralization, but kept a conventional engine location, such as Polaris, gained an advantage when other makers moved their engines back in the chassis.
Mass centralization may sometimes be justified in heavier sleds, but correct mass-distribution in order to give the sled enough inertia to deliver good bump performance becomes more critical the lighter the sled gets. Every manufacturer is making its sleds lighter, and the correct mass distribution will be a critical part of new sled designs to keep the sleds performing well in the moguls