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November 1, 2008
Adjusting Ski Trail
Suspension geometry is not a fixed equation, but spindle angle is. You can’t adjust a spindle to alter a sled’s steering like you can change triple clamps on a motocross bike. But you’re not stuck with the handling characteristics that the sled will have when it leaves the dealership.
One of the most popular ways to affect the handling of a sled’s front end is to replace the stock skis with aftermarket skis. This not only changes the keel, how quickly the sled responds to handlebar input or how well a sled floats, but also opens the doors for more adjustment opportunity.
Most skis—particularly ones like the Starting Line Products SLT which is shown in our diagrams—offer multiple mounting positions that change the keel’s position in relation to the spindle.
What these mounting positions do is allow adjustment of the ski’s trail. What is trail? Trail is when the ski’s keel or contact point with the snow is behind the centerline of the spindle angle. To determine trail, you must draw a line through the centerline of the spindle’s steering axis and then another 90-degree vertical line through the center of the ski’s contact point with the ground. The distance from the spindle’s ground intersect point and the ski’s contact point is the ski’s trail.
Ski trail accounts for the ski’s natural tendency to return to center when the sled is in motion and the rider lets go of the handlebars. Without the outside force of crusty snow or a rut that the ski runner is caught in, the skis would naturally straighten out because their contact point with the snow is “dragging” behind the spindle like a castor wheel on a shopping cart.
This attribute also comes into play when you are riding, whether down hardpacked snow or in the deep powder of the backcountry. On hardpack snow, the less trail a ski has, the more aggressively it will turn (and the more likely it will be to dart). In powder conditions, a ski with less trail will be less inclined to stay in line with the chassis.
More trail means a less aggressive sled with slower steering but a more stable feel. Less trail means just the opposite or a more aggressive sled with more responsive steering (requiring more rider input and attention).
On a ski like the SLT, where you have two mounting holes in the saddle, you get about three-quarters an inch of trail adjustment. Typically, for mountain riding, we mount our SLT skis in the rear hole, which moves the ski bottom back in relation to the spindle and ski saddle. In racing conditions, we would run the ski in the forward hole for more responsive steering.
Each ski is different in its adjustability and steering characteristics. Like any other adjustment change, you should ride with the ski in both positions to determine which is better for your riding style. Many skis, including OEM skis, don’t offer any trail adjustment. But the ones that do give you an advantage over the unchangeable spindle angle.
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