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Ackermann Steering[edit]

Ackermann steering refers to a steering setup in which the inside wheel turns more sharply than the outside wheel. This is done to let both wheels turn around the same point. If the wheels turn around different points, one will scrub or lose grip. This is most important at low speeds, when slip angles are negligible.

Ackermann steering geometry can be created by drawing a line through the kingpin axis and outboard tie rod mounting point, and having this line intersect the midpoint of the rear axle (or equivalent). See diagrams for better explanations. Ackermann1.jpg

Slip Angle[edit]

Slip angle is an important concept of suspension, steering and vehicle dynamics. To understand slip angle, first picture a round rubber disk with a round, flat metal plate on either side of it; the rubber is sandwiched between the plates. If this is placed vertically on a table and held in place at the top, and a lateral force is applied to the center, the rubber disk will deform. The top and bottom of the disk will be held in place by friction, but the disk will deform so the middle (where the force is applied) is not directly above the bottom or below the top. The amount of deformation depends on the lateral force applied.

This disk is an analogy to a tire; when a lateral force is applied to a tire, it deforms similarly. If a steady lateral force is applied, and the tire is rotated/rolled forward, it will not travel in a straight line. The tire itself will remain pointed straight ahead, but its path will be a straight line at an angle to "straight ahead"; this angle is called the slip angle. This occurs because the tire is deformed, so the parts of the tire not contacting the ground are offset slightly from the contact patch. For example, if a force to the right is applied to the tire, the contact patch will be slightly left of the rest of the tire. Therefore, when the tire is rolled, the portion of the tire that now comes into contact with the road is offset from the contact patch. The next patch will be offset from this one, and so on. This creates lateral movement of the tire, although the tire still points straight. See diagrams for clarification. SlipAngle1.jpg