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The snowmobile having a longitudinal axis, a chassis, a pair of skis each having a steering spindle, and a suspension system. The suspension system comprises, for each ski, a first control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis and having a first pivotal c

The snowmobile having a longitudinal axis, a chassis, a pair of skis each having a steering spindle, and a suspension system. The suspension system comprises, for each ski, a first control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis and having a first pivotal connection to the spindle and a second control arm pivotally mounted to the chassis for pivotal movement about a second pivot axis and having a second pivotal connection to the spindle spaced from the first connection. The pivot axis of each control arm and the connection of that control arm to the spindle define a control arm plane; the control arm planes intersect to define a control line that intersects a vertical plane containing said longitudinal axis.

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1. A snowmobile having a longitudinal axis and a chassis, a pair of skis each having a steering spindle defining a steering axis, and a suspension system joining each steering spindle to the chassis, the suspension system comprising, for each ski, a first control arm pivotally mounted to the chassis

1. A snowmobile having a longitudinal axis and a chassis, a pair of skis each having a steering spindle defining a steering axis, and a suspension system joining each steering spindle to the chassis, the suspension system comprising, for each ski, a first control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis and having a first connection to the spindle, a second control arm pivotally mounted to the chassis for pivotal movement about a second pivot axis and having a second connection to the spindle spaced from the first connection, the pivot axis of each control arm and the connection of that control arm to the spindle defining a control arm plane, said control arm planes intersecting to define a control line that intersects a vertical plane containing said longitudinal axis.2. The snowmobile of claim 1 wherein said control arms for each ski continuously control the orientation of the steering spindle to define a steering axis for that ski, said control arms being configured to increase caster of the steering axis as the suspension for that ski is compressed.3. The snowmobile of claim 1 wherein said control line for each ski intersects said vertical plane rearwardly of the steering spindle of that ski.4. The snowmobile of claim 1 wherein said control line for each ski intersects said vertical plane forwardly of the steering spindle of that ski.5. The snowmobile of claim 1 wherein said pivot axes are substantially parallel when viewed from the side but are substantially non-parallel when viewed from the top of the snowmobile.6. The snowmobile of claim 1 wherein said pivot axes are substantially parallel when viewed from the top but are substantially non-parallel when viewed from the side of the snowmobile.7. The snowmobile of claim 1 wherein said pivot axes are substantially non-parallel when viewed either from the side or from the top of the snowmobile.8. The snowmobile of claim 2 wherein said snowmobile has a resting center of gravity and wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point, relative to ground level, of ±1.2 times the height of said center of gravity.9. The snowmobile of claim 8 wherein said snowmobile has a resting center of gravity and wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point not lower than the ground upon which the snowmobile rests and not higher than about 1.2 times the height of said center of gravity.10. The snowmobile of claim 8 wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point spaced rearwardly from the ski pivot by a distance not exceeding about four snowmobile lengths.11. The snowmobile of claim 2 wherein said control arms are so oriented with respect to the chassis and steering spindle that when said suspension is compressed from partial toward full compression, the camber angle of the ski is moved in the negative direction.12. The snowmobile of claim 1 wherein said control arms are vertically separated upper and lower control arms and wherein the lower control arm is generally A-shaped with its ends having pivotal connections to the chassis to define said second pivot axis.13. The snowmobile of claim 12 including a shock absorber for each ski, each shock absorber being attached at a lower end to the lower control arm spaced from the chassis and at an upper end to the chassis and oriented to enable the motion ratio of the suspension to increase as the suspension is compressed.14. The snowmobile of claim 13 wherein the motion ratio increases from a value in the range of 0.4?0.7 to a value in the range of 0.5?0.8 as said suspension is compressed from a rest condition to a fully compressed condition.15. The snowmobile of claim 12 wherein the upper control arm is generally A-shaped with its ends pivotally attached to the chassis to define said first pivot axis.16. The snowmobile of claim 1 wherein the upper control arm includes a link operatively attached at one end to said spindle and at its other end pivotally to the chassis to define said first pivot axis.17. The snowmobile of claim 1 wherein said first and second pivot axes, when viewed from the top, extend rearwardly and outwardly from said vertical plane.18. The snowmobile of claim 1 wherein said first and second pivot axes, when viewed from the side and at rest, each extend rearwardly and downwardly.19. The snowmobile of claim 9 wherein, as said suspension is compressed, said point where said pivot axes appear to intersect is positioned to restrain diving of the forward end of the snowmobile.20. A snowmobile having a longitudinal axis and a chassis, a pair of skis each having a steering spindle defining a steering axis, and a suspension system joining each steering spindle to the chassis, the suspension system comprising, for each ski, a first control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis and a second control arm spaced from the first control arm and pivotally mounted to the chassis for pivotal movement about a second pivot axis, said control arms extending operatively between the chassis and the steering spindle to continuously define the steering axis as the suspension system is compressed, each of said control arm pivot axes defining, with the associated connection to the steering spindle, a control arm plane, said control arm planes intersecting to define a control line that intersects a vertical plane containing said longitudinal axis, the control arms of each ski suspension being so oriented as to cause the camber angle of the ski to move in the negative direction as that suspension is compressed from partial compression toward its fully compressed condition.21. The snowmobile of claim 20 wherein said snowmobile has a resting center of gravity and wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point, relative to ground level, of ±1.2 times the height of said center of gravity.22. The snowmobile of claim 21 wherein said snowmobile has a resting center of gravity and wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point not lower than the ground upon which the snowmobile rests and not higher than about 1.2 times the height of said center of gravity.23. The snowmobile of claim 21 wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point spaced rearwardly from the ski pivot by a distance not exceeding about four snowmobile lengths.24. The snowmobile of claim 20 wherein said control arms are vertically separated upper and lower control arms and wherein the lower control arm is generally A-shaped with its ends having pivotal connections to the chassis to define said second pivot axis.25. The snowmobile of claim 24 including a shock absorber for each ski, each shock absorber being attached at a lower end to the lower control arm spaced from the chassis, and at an upper end to the chassis and oriented to enable the motion ratio of the suspension to increase as the suspension is compressed.26. The snowmobile of claim 25 wherein the motion ratio increases from a value in the range of 0.4?0.7 to a value in the range of 0.5?0.8 as said suspension is compressed.27. The snowmobile of claim 20 wherein, as each suspension is compressed, said intersection point of said control line with said vertical plane moves downwardly to increase the caster angle of the steering spindle.28. The snowmobile of claim 23 wherein, as said suspension is compressed, said point where said pivot axes appear to intersect is positioned to restrain diving of the forward end of the snowmobile.29. A snowmobile having a longitudinal axis and a chassis, a pair of skis each having a steering spindle defining a steering axis, and a suspension system joining the steering spindle to the chassis, the suspension system comprising, for each ski, an upper A-shaped control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis and a lower A-shaped control arm spaced beneath the first control arm and pivotally mounted to the chassis for pivotal movement about a second axis, said control arms extending operatively between the chassis and the steering spindle to continuously define the steering axis as the suspension system is compressed, the control arms, at rest, defining first and second planes that intersect rearwardly to define a control line that itself intersects a vertical plane containing the longitudinal axis of the snowmobile, said A-shaped control arms being so oriented with respect to the chassis and steering spindle as to cause the caster angle to increase and the camber angle of the ski to move in the negative direction as the suspension is compressed from a partially compressed condition toward a fully compressed condition.30. The snowmobile of claim 29 wherein said snowmobile has a resting center of gravity and wherein the first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point, relative to ground level, of ±1.2 times the height of said center of gravity.31. The snowmobile of claim 29 wherein said snowmobile has a resting center of gravity and wherein the first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point not lower than the ground upon which the snowmobile rests and not higher than about 1.2 times the height of said center of gravity.32. The snowmobile of claim 29 including a shock absorber operatively connected between the chassis and the lower A shaped control arm and oriented such that as the suspension system is compressed, the motion ratio of movement along the axis of the shock absorber to vertical movement of the spindle increases to thereby increase ski rate as the suspension is compressed.33. The snowmobile of claim 32 wherein said shock absorber is so positioned that when the front suspension is compressed from a rest position to a substantially fully compressed condition, the motion ratio increases from a value in the range of 0.4?0.7 to a value in the range of 0.5?0.8.34. A snowmobile having a longitudinal axis and a chassis, a pair of skis each having a steering spindle defining a steering axis, and a suspension system joining each steering spindle to the chassis, the suspension system comprising, for each ski, a first control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis, a second control arm spaced from the first control arm and pivotally mounted to the chassis for pivotal movement about a second pivot axis, said first and second pivot axes being fixed with respect to each other and with respect to the chassis, said control arms extending between the chassis and the steering spindle to continuously define the steering axis as the suspension system is compressed, said first and second pivot axes being non-parallel and said control arms being so attached to said steering spindle that when said suspension is compressed toward a fully compressed condition, the caster angle of the steering spindle is increased and the camber angle of the ski is moved in the negative direction.35. The snowmobile of claim 34 wherein said snowmobile has a resting center of gravity and wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point, relative to ground level, of ±1.2 times the height of said center of gravity.36. The snowmobile of claim 34 wherein said snowmobile has a resting center of gravity and wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point not lower than the ground upon which the snowmobile rests and not higher than about 1.2 times the height of said center of gravity.37. The snowmobile of claim 36 wherein said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point spaced rearwardly from the ski pivot by a distance not exceeding about four snowmobile lengths.38. The snowmobile of claim 34 wherein said control arms are vertically separated upper and lower control arms and wherein the lower control arm is generally A-shaped with its ends pivotally attached to the chassis to define said second pivot axis.39. The snowmobile of claim 34 including a shock absorber for each ski, each shock absorber being attached at a lower end to the lower control arm spaced from the chassis, and at an upper end to the chassis and oriented to enable the motion ratio of the suspension to increase as the suspension is compressed.40. The snowmobile of claim 39 wherein the motion ratio increases from a value in the range of 0.4?0.7 to a value in the range of 0.5?0.8 as said suspension is compressed.41. The snowmobile of claim 34 wherein said first and second pivot axes, as viewed from the top, extend rearwardly and outwardly from a vertical plane that contains the longitudinal axis of the snowmobile.42. Method of continuously controlling the caster angle of the steering spindle of a snowmobile ski as the ski suspension is compressed, comprising providing a ski suspension system joining each steering spindle to the chassis, the suspension system comprising, for each ski, a first control arm pivotally mounted to the chassis for pivotal movement about a first pivot axis and having a first connection to the spindle, a second control arm pivotally mounted to the chassis for pivotal movement about a second pivot axis and having a second connection to the spindle spaced from the first connection, the pivot axis of each control arm and the connection of that control arm to the spindle defining a control arm plane, said control arm planes intersecting to define a control line that intersects a vertical plane containing said longitudinal axis, the control arms for each ski being oriented to increase caster of the steering axis as the suspension for that ski is compressed.43. The method of claim 42 including orienting said control arms such that as the suspension for a ski is compressed toward full compression, the camber angle for that ski is moved in the negative direction.44. The method of claim 42 including mounting a shock absorber for each ski between a lower end of a lower control arm and the chassis, the shock absorber being so mounted as to enable the motion ratio of the suspension to increase as the suspension is compressed.45. The method of claim 42 in which said first and second pivot axes appear to intersect, as viewed from the side and at rest, at a point not lower than the ground upon which the snowmobile rests and not higher than about 1.2 times the height of said center of gravity to restrain the snowmobile from diving.