Wheel balancing is the process of equalizing the weight of the combined tyre and rim so that it spins smoothly at high speed. Balancing involves putting the wheel on a balancer, which centers the wheel and spins it to determine where the weights should go.
In essence, wheels and tyres are never exactly the same weight all around. The wheel’s valve stem hole (where you add air to your tyre) will usually subtract a small amount of weight from that side of the wheel. Tyres will also have slight weight imbalances, because that kind of perfection is impossible to achieve. At high speeds, a tiny imbalance in weight can easily become a large imbalance in centrifugal force, causing the wheel to spin with a kind of “galumphing” motion. This usually translates into a vibration in the car as well as some very irregular and damaging wear on the tyres.
The most important things to know about balancing are:
- Balancing Is Necessary: A weight imbalance in every wheel is pretty much inevitable. Only once in a blue moon do we see an assembly come out naturally and perfectly balanced. Discovering a balance is just as much a function of the machine as discovering an imbalance.
- Balance Changes Over Time: As the tyres wear, the balance will slowly and dynamically change over time. Some tyre places will want to rebalance when tyres are rotated. Rebalancing over the life of the tyres will almost certainly extend said lifetime.
- Balancing Only Fixes Balance: Balancing will not prevent vibrations from a bent wheel, out of round tyre or irregular wear. Balancing weights can’t compensate for a problem that is actually physical in nature, they can only compensate for weight differences. One of the first mathematical assumptions the balancer’s brain makes is that the wheel and tyre are both round to within a certain maximum deviation, so if a wheel is substantially bent, for example, the balancer will probably end up getting the weight placement wrong in the first place.