Land vehicles, such as for example snowmobiles, typically include a chassis having a rear portion that is supported and driven on the ground by a track and a front portion that is supported and steered on the ground by a pair of ground contacts, typically including skis. A pair of opposed suspension assemblies connect the front portion of the chassis to the ground contacts and support the chassis during travel. The opposed suspension assemblies each define a steering axis for the vehicle and extend in three dimensions including a length dimension, a radial dimension that is substantially perpendicular to the length dimension, and a vertical dimension that is substantially perpendicular to the length dimension and substantially perpendicular to the radial dimension.
The spatial positioning and movement of the suspension assemblies and related steering axes are often defined in terms of, among other things, camber, caster, caster trail, toe, and roll center height. Camber is the angle of the steering axes relative to vertical, as viewed from the front or the rear of the vehicle. If the steering axis leans in towards the chassis, it has negative camber; if the axis leans away from the chassis, it has positive camber. Caster is the angle to which the steering axes are tilted forward or rearward from vertical, as viewed from the side. If the steering axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then caster is positive; if the axis is tilted forward, then caster is negative. Caster trail is the distance in side elevation between the point where the steering axis intersects the ground, and the center of the ground contact patch. Caster trail is considered positive when the intersection point is forward of the ground contact center and negative when it is rearward of the ground contact center. When the ground contacts are set so that their leading edges are pointed towards each other, the ground contacts are said to have toe-in. If the leading edges point away from each other, the ground contacts are said to have toe-out. The amount of toe can be expressed in degrees to which the ground contacts are out of parallel, or more commonly, as the difference between the track widths as measured at the leading and trailing edges of the ground contacts. Roll center height is the point in the transverse vertical plane through any pair of ground contact points at which lateral forces may be applied to the sprung mass without producing suspension roll.