Toe (automotive)

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Image of front toe angle 5 degrees (toe in) Toe-in example 5 degrees positive.png
Image of front toe angle 5 degrees (toe in)

In automotive engineering, toe, also known as tracking, [1] is the symmetric angle that each wheel makes with the longitudinal axis of the vehicle, as a function of static geometry, and kinematic and compliant effects. This can be contrasted with steer, which is the antisymmetric angle, i.e. both wheels point to the left or right, in parallel (roughly). Negative toe, or toe out, is the front of the wheel pointing away from the centreline of the vehicle. Positive toe, or toe in, is the front of the wheel pointing towards the centreline of the vehicle. [2] Historically, and still commonly in the United States, toe was specified as the linear difference (either inches or millimeters) of the distance between the two front-facing and rear-facing tire centerlines at the outer diameter and axle-height; since the toe angle in that case depends on the tire diameter, the linear dimension toe specification for a particular vehicle is for specified tires. [3]



In a rear-wheel drive vehicle, increased front toe-in provides greater straight-line stability at the cost of some sluggishness of turning response. Performance vehicles may run zero front toe or even some toe-out for a better response to steering inputs. Increased front toe-in marginally increases the wear on the tires as the tires are under slight side slip conditions when the steering is set straight ahead. On front-wheel drive vehicles, the situation is more complex. Rear toe-in provides better stability during cornering.

Toe is usually adjustable in production automobiles, even though caster angle and camber angle are often not adjustable. Maintenance of front-end alignment, which used to involve all three adjustments, currently involves only setting the toe; in most cases, even for a car in which caster or camber are adjustable, only the toe will need adjustment. Toe may only be adjustable on the front wheels.

One related concept is that the proper toe for straight-line travel of a vehicle will not be correct while turning, since the inside wheel must travel around a smaller radius than the outside wheel; to compensate for this, the steering linkage typically conforms more or less to Ackermann steering geometry, modified to suit the characteristics of the individual vehicle.

Road–rail vehicles

The front rail wheels of road–rail vehicles are often set to toe-in by a distance of 6 mm over 1 metre. Unlike other forms of rolling stock, road-rail vehicles do not always have a common axle between the rail wheels and the toe-in angle prevents the vehicle from hunting when on-rail.

Interaction with camber

When a wheel is set up to have some camber angle, the interaction between the tire and road surface causes the wheel to tend to want to roll in a curve, as if it were part of a conical surface (camber thrust). This tendency to turn increases the rolling resistance as well as increasing tire wear. A small degree of toe (toe-out for negative camber, toe-in for positive camber) will cancel this turning tendency, reducing wear and rolling resistance. On some competition vehicles such as go-karts, especially where power is extremely limited and is highly regulated by the rules of the sport, these effects can become very significant in terms of competitiveness and performance. Toe-in and toe-out give the steering stability.[ citation needed ]

Related Research Articles

Vehicle dynamics is the study of vehicle motion, e.g., how a vehicle's forward movement changes in response to driver inputs, propulsion system outputs, ambient conditions, air/surface/water conditions, etc. Vehicle dynamics is a part of engineering primarily based on classical mechanics. It may be applied for motorized vehicles, bicycles and motorcycles, aircraft, and watercraft.

<span class="mw-page-title-main">Ackermann steering geometry</span> Arrangement of steering linkages

The Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii.

<span class="mw-page-title-main">Camber angle</span> Angle between a wheels vertical axis and the vehicles vertical axis

Camber angle is one of the angles made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of a wheel and the vertical axis of the vehicle when viewed from the front or rear. It is used in the creation of steering and suspension. If the top of the wheel is farther out than the bottom, it is called positive camber; if the bottom of the wheel is farther out than the top, it is called negative camber.

<span class="mw-page-title-main">Steering</span> The control of the direction of motion of vehicles and other objects

Steering is the control of the direction of locomotion.

<span class="mw-page-title-main">Car suspension</span> Suspension system for a vehicle

Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other. The tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.

Automobile handling and vehicle handling are descriptions of the way a wheeled vehicle responds and reacts to the inputs of a driver, as well as how it moves along a track or road. It is commonly judged by how a vehicle performs particularly during cornering, acceleration, and braking as well as on the vehicle's directional stability when moving in steady state condition.

<span class="mw-page-title-main">Caster</span> Undriven wheel that is designed to be attached to the bottom of a larger object

A caster is an undriven wheel that is designed to be attached to the bottom of a larger object to enable that object to be moved.

<span class="mw-page-title-main">Wheelbase</span> Distance between the centers of the front and rear wheels

In both road and rail vehicles, the wheelbase is the horizontal distance between the centers of the front and rear wheels. For road vehicles with more than two axles, the wheelbase is the distance between the steering (front) axle and the centerpoint of the driving axle group. In the case of a tri-axle truck, the wheelbase would be the distance between the steering axle and a point midway between the two rear axles.

<span class="mw-page-title-main">Double wishbone suspension</span> Automotive independent suspension design

A double wishbone suspension is an independent suspension design for automobiles using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as camber angle, caster angle, toe pattern, roll center height, scrub radius, scuff, and more.

<span class="mw-page-title-main">Caster angle</span> The angle between the vertical axis and the steering axis of a steered wheel, in side view

The caster angle or castor angle is the angular displacement of the steering axis from the vertical axis of a steered wheel in a car, motorcycle, bicycle, other vehicle or a vessel, as seen from the side of the vehicle. The steering axis in a car with dual ball joint suspension is an imaginary line that runs through the center of the upper ball joint to the center of the lower ball joint, or through the center of the kingpin for vehicles having a kingpin.

A swing axle is a simple type of independent suspension designed and patented by Edmund Rumpler in 1903. This was a revolutionary invention in automotive suspension, allowing driven (powered) wheels to follow uneven road surfaces independently, thus enabling the vehicle's wheels to maintain better road contact and holding; plus each wheel's reduced unsprung weight means their movements have less impact on the vehicle as a whole. The first automotive application was the Rumpler Tropfenwagen, later followed by the Mercedes 130H/150H/170H, the Standard Superior, the Volkswagen Beetle and its derivatives, the Chevrolet Corvair, and the roll-over prone M151 jeep amongst others.

<span class="mw-page-title-main">Tilting three-wheeler</span> Tilting three-wheeled vehicle

A tilting three-wheeler, tilting trike, leaning trike, or even just tilter, is a three-wheeled vehicle and usually a narrow-track vehicle whose body and or wheels tilt in the direction of a turn. Such vehicles can corner without rolling over despite having a narrow axle track because they can balance some or all of the roll moment caused by centripetal acceleration with an opposite roll moment caused by gravity, as bicycles and motorcycles do. This also reduces the lateral acceleration experienced by the rider, which some find more comfortable than the alternative. The narrow profile can result in reduced aerodynamic drag and increased fuel efficiency. These types of vehicles have also been described as "man-wide vehicles" (MWV).

<span class="mw-page-title-main">Wheel alignment</span> Adjustment of the angles of wheels on a car

Wheel alignment, which is sometimes referred to as breaking or tracking, is part of standard automobile maintenance that consists of adjusting the angles of wheels to the car manufacturer specifications. The purpose of these adjustments is to reduce tire wear and to ensure that vehicle travel is straight and true. Alignment angles can also be altered beyond the maker's specifications to obtain a specific handling characteristic. Motorsport and off-road applications may call for angles to be adjusted well beyond normal, for a variety of reasons.

<span class="mw-page-title-main">Beam axle</span> Automobile mechanism

A beam axle, rigid axle or solid axle is a dependent suspension design in which a set of wheels is connected laterally by a single beam or shaft. Beam axles were once commonly used at the rear wheels of a vehicle, but historically they have also been used as front axles in four-wheel-drive vehicles. In most automobiles, beam axles have been replaced with front and rear independent suspensions.

<span class="mw-page-title-main">Bicycle and motorcycle dynamics</span> Science behind the motion of bicycles and motorcycles

Bicycle and motorcycle dynamics is the science of the motion of bicycles and motorcycles and their components, due to the forces acting on them. Dynamics falls under a branch of physics known as classical mechanics. Bike motions of interest include balancing, steering, braking, accelerating, suspension activation, and vibration. The study of these motions began in the late 19th century and continues today.

The following outline is provided as an overview of and topical guide to automobiles:

The scrub radius is the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. It can be positive, negative or zero.

<span class="mw-page-title-main">Bump steer</span>

Bump steer is the term for the tendency of the wheel of a car to steer itself as it moves through the suspension stroke.

<span class="mw-page-title-main">Twist-beam rear suspension</span>

The twist-beam rear suspension is a type of automobile suspension based on a large H or C-shaped member. The front of the H attaches to the body via rubber bushings, and the rear of the H carries each stub-axle assembly, on each side of the car. The cross beam of the H holds the two trailing arms together, and provides the roll stiffness of the suspension, by twisting as the two trailing arms move vertically, relative to each other.

<span class="mw-page-title-main">Camber thrust</span>

Camber thrust and camber force are terms used to describe the force generated perpendicular to the direction of travel of a rolling tire due to its camber angle and finite contact patch. Camber thrust is generated when a point on the outer surface of a leaned and rotating tire, that would normally follow a path that is elliptical when projected onto the ground, is forced to follow a straight path while coming in contact with the ground, due to friction. This deviation towards the direction of the lean causes a deformation in the tire tread and carcass that is transmitted to the vehicle as a force in the direction of the lean.


  1. "Beardmore Bros How To Do Tracking". Retrieved 20 February 2011. Now adjust the tracking
  2. "Toe-out and Handling, steering geometry & front end alignment". Retrieved 28 August 2011.
  3. "Wheel Alignment: a Short Course".