Tire balance, also known as tire unbalance or tire imbalance, refers to the distribution of mass within an automobile tire or the entire wheel on which it is mounted. During a tire balance service, the tires and wheels are mounted onto a tire balancing machine, which spins the tire and wheel assembly to measure the imbalance. A technician then installs the correct tire weights to achieve a properly balanced wheel and tire assembly. Tire balancing is measured in factories and repair shops by two methods: with static balancers and with dynamic balancers. Tires with large unbalances are downgraded or rejected. When tires are fitted to wheels at the point of sale, they are measured again on a balancing machine, and correction weights are applied to counteract their combined unbalance. Tires may be rebalanced if the driver perceives excessive vibration.
Tire balancing is distinct from wheel alignment. Static balance requires that the center of mass of the tire be aligned with the axis about which it rotates, usually the axle on which it is mounted. Dynamic balance requires that a principal axis of the tires moment of inertia be aligned with the axis about which the tire rotates, usually the axle on which it is mounted.
The most common symptoms of an out-of-balance tire are uneven and faster tread wear, poor fuel economy, or vibration in the steering wheel and/or floorboard that gets worse at faster speeds. If left uncorrected, it can also lead to uneven tread wear, which means the tires could wear out faster. Tires can become out of balance because of uneven tire wear or the loss of a wheel weight because a rim hits a curb or pothole. If a front tire isn’t properly balanced, the driver will likely feel that vibration in the steering wheel. If the problem is in the rear, the driver will feel it in the seat or floor. This vibration can change depending on the speed the vehicle is traveling.
