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The phrase "get your tracking and balancing done" is used in everyday speech as if it were a single job. In fact these are two entirely different procedures; they solve different problems, produce different symptoms, and neither one substitutes for the other. Telling them apart saves you both unnecessary expense and the frustration of "I had it done but it didn't fix anything".

What is wheel balancing?

Balancing is about the mass distribution of the wheel. The tyre and rim rotate together; if their mass is not perfectly evenly distributed around the circumference, the heavier point generates centrifugal force as it spins. This isn't noticeable at low speed, but as speed increases this force grows with the square of the speed and is felt as vibration within a certain speed range. A wheel balancing machine spins the wheel to measure where the weight difference lies, and small balancing weights are fitted to the opposite side of the rim to even it out.

Symptom of imbalance: Vibration that starts within a specific speed band and sometimes eases as speed increases further. On the front wheels the vibration is felt mainly in the steering wheel; on the rear wheels it's felt in the seat and the body of the car. Imbalance does not cause the vehicle to pull to one side and does not wear the tyre unevenly on one edge.

What is wheel alignment?

Wheel alignment, on the other hand, is not about mass but about the angles of the wheels. The wheels must sit at specific angles relative to the road and the vehicle. There are three basic angles:

• Toe: Whether the fronts of the tyres point inwards or outwards when viewed from above. This is the angle with the greatest effect on the car's straight-line tracking and on tyre wear, and it is adjustable on most vehicles. In practice, this is what people mean most of the time when they say "wheel alignment".
• Camber: The angle the wheel makes with the vertical when viewed from the front, i.e. whether the top leans inwards or outwards. It plays the leading role in one-sided wear of the inner or outer shoulder of the tyre.
• Caster: The forward or backward tilt of the steering axis when viewed from the side. It determines the steering's tendency to self-centre after a bend and the vehicle's straight-line stability at high speed.

An important point: not every angle is adjustable on every vehicle. On many cars camber and caster are fixed at the factory setting; when these are found to be out, it usually points to a bent or worn component, and the fix is a repair rather than an adjustment.

Symptom of misalignment: The vehicle pulling to one side when you let go of the steering wheel on a flat, level road; the steering wheel sitting crooked while the car travels straight; one shoulder of a tyre visibly more worn than the other; the steering being reluctant to return to centre after a bend.

When is it needed?

These two jobs are triggered by events, not by a calendar. Typical situations that call for adjustment:

• When new tyres are fitted or tyres are swapped between positions (balancing is essential).
• After a hard impact with a kerb, pothole, or manhole cover (an alignment check is warranted).
• When a suspension and steering component is replaced: control arm, ball joint, tie rod end, shock absorber, spring. All of these affect the geometry; an alignment check after replacement is the correct practice.
• When steering vibration, pulling, or a loss of straight-line tracking begins.
• When uneven wear is noticed on the tread of a tyre.
• When ride height is adjusted or the rim/tyre size is changed.

It would not be accurate to give a fixed figure for a periodic check interval; the condition of the roads you drive on has a major influence on this. The recommendation in your vehicle's owner's manual should be your guide. In practice, having it checked at tyre changes and at the annual service is a sensible habit.

Play first, then adjustment

This is the rule most often skipped. A wheel alignment carried out while there is play in the suspension and steering assembly will not give a correct result. The reason is simple: the alignment machine measures the angle at which the wheel is sitting at that moment. If there is play in a ball joint or tie rod end, the wheel's angle changes under load; in other words, the angle you measured will not hold on the road. The result is a complaint that comes straight back within a short time. This is why a serious workshop checks for play by raising the vehicle before putting it on the alignment machine. Most cases where an adjustment "doesn't hold" are actually a repair that was never carried out.

Likewise, tyre pressures must be correct before the adjustment. Low pressure changes the ride height of the vehicle and therefore the angles being measured.

What happens if it isn't done?

The most visible consequence is the tyre. A wheel running with an incorrect toe angle does not roll straight on the road; it constantly moves forward while scrubbing slightly. This scrubbing wears the tyre quickly and unevenly; the cost of a set of tyres is many times over the cost of an alignment. The second consequence is fuel: a scrubbing wheel increases rolling resistance. The third, and most important, is safety. Steering that constantly needs correcting tires the driver out, and the vehicle's response in an emergency manoeuvre becomes unpredictable; the grip of a tyre with a worn shoulder drops noticeably on wet surfaces.

The continuous vibration produced by an unbalanced wheel places unnecessary load on the bearings, tie rod ends, and steering box. In other words, a small imbalance that's neglected turns, over time, into a bill for the other components of the suspension and steering assembly.

If your vehicle is pulling to one side, vibrating, or showing uneven tyre wear, you can book an appointment with our workshop for a check.