Toe
The vehicle's toe is the most critical alignment settings relative to tyre wear. if the toe setting is just 1/32-inch off of its appropriate setting, this will reduce tyre life.
Like camber, toe will change depending on vehicle speed, as aerodynamic forces changes the riding height hence affecting camber and toe due to the geometry of the steering linkage in relation to the geometry of the suspension.
The toe angle identifies the direction of the tyres compared to the centerline of the vehicle. Rear-wheel drive vehicle "pushes" the front tyres, as they roll along the road, resistance causes some drag resulting in rearward movement of the suspension arms against their bushings. Most rear-wheel drive vehicles use positive toe to compensate for suspension movement.
Front-wheel drive vehicle "pulls" the vehicle, resulting in forward movement of the suspension arms against their bushings. Most front-wheel drive vehicles use negative toe to compensate for suspension movement.
Be aware that toe setting influences tyre wear. Excessive toe settings often causes drivability problems, especially during heavy rain. This is because most highways have tyre groves from the daily use by Lorries and trailers. These heavy vehicles leave groves that fill with water. When one of the vehicles front tyre encounters a puddle, it loses some of its grip, the other tyre's toe setting will push causing excessive toe-in, or pull causing excessive toe-out. This may cause the vehicle to feel unstable.
Perhaps the easiest concept to visualize is toe. Toe represents the angle derived from pointing the tyres inward or outward from a top-down view - much like looking down at your toes and angling them inward or outward.
Correct toe is paramount to even tread wear and extended tyre life. If the tyres are pointed inward or outward, they will scrub against the surface of the road and cause wear along the edges. Sometimes however, tread life can be sacrificed for performance or stability
Positive toe occurs when the front of both tyres begins to face each other. Positive toe permits both wheels to constantly generate force against one another, which reduces turning ability. However, positive tow creates straighter driving characteristics.
Typically, rear wheel drive vehicles have slightly positive tow in the rear due to rolling resistance - causing outward drag in the suspension arms. The slight positive toe straightens out the wheels at speed, effectively evening them out and preventing excessive tyre wear.
Negative toe is often used in front wheel drive vehicles for the opposite reason. Their suspension arms pull slightly inward, so a slight negative toe will compensate for the drag and level out the wheels at speed.
Negative toe increases a cars cornering ability. When the vehicle begins to turn inward towards a corner, the inner wheel will be angled more aggressively. Since its turning radius is smaller than the outer wheel due to the angle, it will pull the car in that direction.
Negative toe decreases straight line stability as a result. Any slight change in direction will cause the car to hint towards one direction or the other.
Conclusion
Vehicles are designed with manufacturer's settings for a reason. Countless hours of research and development go into designing suspension components and typically those numbers are the best to go with. Attempting to differ from the norm may result in dangerous conditions, especially for public road vehicles.
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