The name is fairly self-explanatory, and the job is intended to ensure that the weight of a wheel and tyre together is the same all the way around its rotation on the axle.
Balancing can be done on a special machine which measures the weight being exerted at all points in the wheel’s rotation cycle. When they need to balance a wheel, a mechanic or technician will place small offsetting weights at a series of specific points around the outside of a wheel.
These weights will help identify any point around the wheel’s circumference where excessive weight is being exerted.
Three different adjustments can be made to correct the alignment of a vehicle’s wheels:
- Toe – this refers to how much wheels point outwards or inwards. You can think of this in the same way as your feet; if they’re not straight as you walk (as they rarely are), you’ll soon notice that one corner of your shoes will wear more quickly than the other.
- Camber – a measure of how far the wheels lean towards or away from your car when they are supposedly straight. Leaning too far outwards leads to excess wear on the outer edges of the tyres, and too far inwards means the inner edges will deteriorate more quickly.
- Caster – this describes the amount of forward or backward tilt in your steering axis. Poor balance between the two steering arms may eventually cause the back and front ends of your car to become misaligned. Uneven tyre wear may again result, but in the most serious cases, this could lead to the vehicle becoming unstable at even reasonably modest speeds of 40-50mph.
There are two types of road wheel balancing: standard balancing and road force balancing. The former simply involves the wheel being checked when it is off the car, while the latter involves the car being placed on a rolling road, just as those you’ll see at any MoT testing centre.
This will identify a wheel which is not truly round, or uneven tread or wall stiffness in a tyre. This will exacerbate any problems of vibration encountered when a wheel is not properly balanced.
Road force imbalance is corrected, and the vibration it leads to solved, by the tyre being rotated on the wheel rim, so that the stiff spot in a tyre is matched to the low spot on the rim. In instances where this isn’t possible, however, the tyre will need to be replaced.
If you still experience vibration through your car wheels, you should check your tyre pressures, as wide disparities in these can cause that ‘wobble’ – but this is probably the easiest, and cheapest, solution.