When a wheel is unbalanced, there is an unequal distribution of weight around the rim of the wheel and tire assembly. The tire may seem round and true when rotated slowly, but on the road centrifugal force acts on the heaviest part of the tire, making it wobble or vibrate (like an out-of-balance ceiling fan). This can cause flat spots on the tire treads and is damaging to ball joints, bearings, steering, and shock absorbers. With special equipment, technicians can measure a tire and wheel assembly, then add special wheel weights to restore balance. Hitting potholes and normal vehicle wear and tear can cause unbalanced wheels. Uneven tire wear can indicate unbalanced wheels, so it's wise to check and rotate your vehicle's tires regularly.