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Related to toe-in: caster


[′tō ‚in]
(mechanical engineering)
The degree (usually expressed in fractions of an inch) to which the forward part of the front wheels of an automobile are closer together than the rear part, measured at hub height with the wheels in the normal “straight ahead” position of the steering gear.



symmetrical inclination of the front wheels of a motor vehicle at an angle to the vehicle’s longitudinal axis in such a way that the wheels are closer together at the front than at the back. Toe-in is necessary because the wheels have a camber and therefore tend to roll along divergent arcs. Toe-in eliminates this tend.

Figure 1. Toe-in in a motor vehicle, equal to the difference between the distances A and B: (1) transverse centerlink

ency and makes the wheels roll along parallel straight lines. Improper toe-in results in excessive tire wear and vehicle instability. Toe-in is equal to the difference between the distances A and B as illustrated in Figure 1; it ranges between 2 and 8 mm, depending on the vehicle model. It can be regulated by means of adjustable tie rods and the transverse centerlink, which are equipped with threaded ends.


Note: Toe-in of wheels has been exaggerated.
Note: Toe-in of engines has been exaggerated.
i. Aircraft wheels that tend to converge toward the front (i.e., a line drawn through the center of two wheels, is perpendicular to the axles, and crosses ahead of the wheels).
ii. Aircraft left and right engines having their axes, which in a horizontal plane are inclined to meet the aircraft centerline, ahead of the nose.