What balancing does
No tire and wheel assembly is perfectly even. Small differences in weight distribution around the assembly are harmless at low speed and become a problem as the wheel spins faster, because the out-of-balance mass is thrown outward harder with every increase in speed.
Balancing measures where the assembly is heavy and adds small counterweights to even it out. The result is an assembly that spins without shaking the vehicle.
Why it matters beyond comfort
A vibration is the symptom. The damage is elsewhere:
- Uneven tread wear, in patches, which shortens the life of a new set.
- Wear in the suspension, because every component is being shaken continuously.
- Steering and bearing wear on the same principle.
- Casing damage on commercial tires, which can cost a casing its retread life. See retreading.
When to have it done
- Whenever a tire is fitted. This is the main one, and it is standard practice.
- When a vibration appears, particularly one that comes in at a particular speed and fades above or below it.
- After hitting something hard enough to knock a weight off or damage the wheel.
- If a wheel weight is visibly missing, which is worth looking for after a curb strike.
Balancing against alignment
They get confused. The quick version:
- Balancing fixes a vibration and is about weight distribution around the wheel.
- Alignment fixes a pull, a crooked steering wheel and uneven wear across the tread, and is about the angles the wheels sit at.
A vibration at speed is usually balance. A car that pulls or wears one edge is usually alignment. Both can be true at once, which is why a store will look at both when a new set goes on.
Commercial and off-highway
Balancing is not just a car service. Commercial truck assemblies are balanced for the same reasons and with more at stake, since the vibration is being fed into a vehicle that runs far more miles. Fleets using fleet services have balancing built into fitting as standard.