Wheel alignment is part of standard automobile maintenance that consists of adjusting the angles of the wheels so that they are set to the car maker’s specification. The purpose of these adjustments is to reduce tire wear, and to ensure that vehicle-travel is straight and true (without “pulling” to one side). 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.
Tire rotation or rotating tires is the practice of moving automobile wheels and tires from one position on the car, to another, to ensure even tire wear. Tire wear is uneven for any number of reasons. Even tire wear is desirable to maintain consistent performance in the vehicle and to extend the overall life of a set of tires.
By design, the weight on the front and rear axles differs which causes uneven wear. With the majority of cars being front-engine cars, the front axle typically bears more of the weight. For rear wheel drive vehicles, the weight distribution between front and back approaches 50:50. Front wheel drive vehicles also have the differential in front, adding to the weight, with a typical weight distribution of no better than 60:40. This means, all else being equal, the front tires wear out at almost twice the rate of the rear wheels, especially when factoring the additional stress that braking puts on the front tires. Thus, tire rotation needs to occur more frequently for front-wheel drive vehicles.
Turning the vehicle will cause uneven tire wear. The outside, front tire is worn disproportionately. Cloverleaf interchanges, and parking ramps turn right in left hand drive (otherwise known as right hand traffic) countries, causing the left front tire to be worn faster than the right front. Furthermore, right turns are tighter than left turns, also causing more tire wear. Conversely the sidewalls on the right tire tends to be bumped and rubbed against the curb while parking the vehicle, causing asymmetric sidewall wear. The symmetric opposite occurs in countries that drive on the left.
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose – contributing to the car’s roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations,etc. These goals are generally at odds, so 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 forces acting on the vehicle do so through the contact patches of the tyres. 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.
Corner Weighting is the process of shifting the weight carried by each wheel to approach optimal values. Although some weight can be shifted between wheels by physically relocating parts of the car, the corner balance process is focused on shifting weight by adjusting the suspension spring height. Any relocation of parts should be performed before corner balancing begins.
Tire balance, also referred to as tire unbalance or imbalance, describes the distribution of mass within an automobile tire and/or the wheel to which it is attached. When the tire rotates, asymmetries of mass cause the wheel to wobble for reasons discussed below. This wobbling can give rise to ride disturbances, usually vertical and lateral vibrations. The ride disturbance due to unbalance usually increases with speed. Vehicle suspensions can be excited by tire unbalance forces when the speed of the wheel reaches a point that its rotating frequency equals the suspension’s resonant frequency. Tires are inspected in factories and repair shops by two methods: static balancers and dynamic balancers. Tires with high unbalance forces are downgraded or rejected. When tires are fitted to wheels at the point of sale, they are measured again, and correction weights are applied to counteract the combined effect of the tire and wheel unbalance.