Car Wheel Alignment: Signs, Benefits and How It Works

Wheel alignment is one of those jobs that never feels urgent until you are buying tyres twice as often as you should be. It costs little, takes under an hour at most tyre specialists, and it quietly determines how long your tyres last, how the car steers and how much fuel it uses.

What is car wheel alignment?

Wheel alignment is the process of adjusting the angles at which your wheels sit relative to each other, to the car and to the road surface.

When the alignment is right, the tyres sit flat on the road, point in the direction the car is travelling, and share the work evenly between all four corners. When it is wrong, one or more tyres are dragged slightly sideways every metre you drive, which is exactly as destructive as it sounds.

Alignment is set by the manufacturer for each model and adjusted by moving the suspension mounting points and the track rods. It is not a single measurement but three separate angles, and a car can be correct on one and wrong on another.

What are camber, caster and toe?

These are the three angles that make up an alignment, and each affects the car differently.

Camber is negative when the top of the wheel leans inwards and positive when it leans outwards. A small amount of negative camber is designed in on most cars, because it keeps the tyre flat on the road when the body rolls in a corner. Too much of it in either direction wears one edge of the tread away.

Caster is the angle you can see on a supermarket trolley wheel, and it does the same job: it makes the wheel want to trail behind the pivot point and self centre. Correct caster gives you a car that tracks straight on the motorway and returns the steering wheel to centre by itself after a roundabout.

Toe is the one that costs the most money when it is wrong. Even a small toe error means the tyre is being pushed sideways across the road surface for its entire life. Feathered tread edges that you can feel by running a hand across the tyre are the classic sign.

What are the signs that your wheels are misaligned?

Uneven tyre wear, a car that pulls to one side, and a steering wheel that is not centred on a straight road are the three signs that show up first.

Look for:

• Uneven wear across a tyre. One shoulder worn and the other fine is the clearest indicator
• Feathering. Run your hand across the tread. If it feels smooth one way and sharp the other, the toe is out
• The car pulls. Find a flat, straight road with no camber, ease off the wheel briefly, and see whether the car holds its line
• An off centre steering wheel. If you are going straight but the wheel sits at ten past or ten to, the toe settings are uneven side to side
• Loose or wandering steering. The car needs constant small corrections to hold a lane
• Squealing tyres in slow corners. Tyres protesting at low speed often means toe is well out

Road camber will make almost any car drift slightly left on a British road, so test on the flattest surface you can find before deciding the car has a fault.

Why does wheel alignment matter?

Correct alignment saves tyres, improves fuel economy, makes the car steer predictably and reduces the load on suspension components.

• Tyre life. This is the big one. Misaligned tyres can wear out in a fraction of their normal life, and the wear pattern often makes them unsafe well before the tread hits the legal limit
• Fuel economy. Tyres dragged sideways create rolling resistance, and the engine burns fuel overcoming it
• Handling and safety. Aligned wheels respond predictably to steering input. Misaligned ones make emergency manoeuvres less certain, particularly on a wet road
• Suspension wear. A car fighting itself puts continuous load into bushes, ball joints and wheel bearings
• MOT. Tyres worn unevenly below the limit at any point across the tread will fail the test, even if the rest of the tyre looks new

The legal minimum tread depth in the UK is 1.6 mm across the central three quarters of the tread and around the whole circumference. A tyre worn to the canvas on one shoulder fails, whatever the middle looks like.

What knocks a car out of alignment?

Impacts are the main cause, and British road surfaces provide plenty of them.

• Potholes. The most common single cause. A deep one taken at speed can shift camber and toe in one hit
• Kerb strikes. Even a gentle one while parking. Kerbing the front wheel is enough
• Speed bumps taken too fast
• Worn suspension components. Perished bushes and worn ball joints let the geometry move under load, so the car may measure correctly on the ramp and still misbehave on the road
• Normal wear over time. Alignment drifts gradually even without an incident
• Suspension or steering work. Anything that involves loosening a suspension joint should be followed by an alignment check
• Uneven loading. Regularly carrying heavy loads on one side changes ride height, which changes camber

How often should alignment be checked?

Many garages suggest a check every six months or around every 6,000 miles, and again straight after any significant impact.

In practice, the sensible triggers are:

• After hitting a pothole hard enough to make you wince
• After kerbing a wheel
• When fitting new tyres
• After any suspension or steering repair
• Any time you notice uneven tyre wear, a pull, or an off centre steering wheel
• At the annual service, as a routine check

A check costs far less than a tyre. If you drive a lot of urban miles, on the sort of patched and potholed roads common across Greater Manchester, checking more often than the general advice is easy to justify.

What happens during a wheel alignment?

The car goes onto a level ramp, sensors or targets are clamped to each wheel, and the equipment measures every angle against the manufacturer's specification before anything is adjusted.

The typical process:

• Preliminary checks. Tyre pressures set correctly, tyre condition assessed, suspension and steering checked for play. There is no point aligning a car with a worn track rod end, because the measurement will not hold
• Measurement. Targets are fitted to all four wheels and the car is measured. The equipment produces a printout showing each angle against the tolerance for that model
• Adjustment. The technician adjusts what is adjustable. Toe is adjustable on almost every car. Camber and caster are adjustable on some models and fixed on others, which occasionally means fitting adjustable components
• Rechecking. The car is measured again and, where fitted, the steering angle sensor is reset so the driver assistance systems know where straight ahead is
• Road test. A short drive to confirm the car tracks straight and the wheel is centred

Ask for the before and after printout. It is the only proof that the work changed anything.

Two wheel or four wheel alignment: which do you need?

A four wheel alignment is the right choice on almost any modern car, because the rear axle sets the reference the front is aligned to.

If the rear axle is not tracking straight, aligning only the front leaves the car crabbing slightly down the road with the steering wheel off centre. That is why a cheap front toe adjustment sometimes fails to cure a pull.

Do driver assistance systems need recalibrating after alignment?

On cars fitted with lane keeping, adaptive cruise control or automatic emergency braking, yes, and it is easy to overlook.

Those systems rely on a forward facing camera behind the windscreen, radar sensors in the grille or bumper, and a steering angle sensor in the column. They are calibrated against the car's thrust line, which is set by the rear axle. Change the geometry and the camera is now looking slightly off from where the car actually travels, so lane markings are read fractionally out of position and the steering angle sensor reports the wrong figure for straight ahead.

The symptoms are subtle rather than dramatic: lane keep assist nudging the car towards one side of the lane, adaptive cruise picking up the vehicle in the next lane, or a lane departure warning that goes off for no reason. A garage with the right equipment resets the steering angle sensor as part of the alignment and can recalibrate the camera where the manufacturer requires it. Ask before you book if your car has these systems, because not every alignment centre is set up for it.

The same applies after windscreen replacement and after any front end bodywork, since both disturb the sensor mountings.

Can you do a wheel alignment yourself?

Realistically, no. The tolerances are measured in fractions of a degree and the equipment needs a genuinely level surface, so home methods rarely get close enough to be worth the effort.

String and straight edge methods can get toe into the right region on a track car where you can afford to experiment, but on a road car the risk is that you make things worse and then wear out a set of tyres proving it. The one useful thing you can do yourself is diagnosis: check pressures, read the wear patterns, and go to the alignment specialist knowing what you are asking them to look at.

How alignment and tyre wear are connected

The wear pattern on a tyre is a record of what the alignment has been doing, and each pattern points at a specific fault.

Fixing the alignment stops the wear getting worse but does not restore a tyre that has already worn into a pattern. If the wear is significant, budget for the tyre as well as the alignment.

How does suspension condition affect alignment?

Worn suspension components let the geometry change as the car moves, so a car can be perfectly aligned on the ramp and still wear tyres unevenly on the road.

The parts that matter most are the wishbone bushes, ball joints, track rod ends and anti roll bar drop links. Perished rubber bushes are the usual culprit: under braking and cornering the wheel moves further than the designer intended, and the toe setting changes with it.

Any competent alignment technician will check for play before measuring, and will tell you if a component needs replacing first. If they do not check, the alignment printout is not worth much.

Common myths about wheel alignment

A few things get repeated often enough to be worth correcting.

• "Alignment only affects tyre wear." It also affects steering feel, straight line stability, braking behaviour and fuel consumption
• "If it does not pull, the alignment is fine." Not true. Toe can be well out on both sides equally, which scrubs both front tyres without producing any pull at all
• "Alignment and balancing are the same thing." They are separate jobs solving separate problems
• "New cars do not need checking." They come out of the factory in tolerance, but the first serious pothole does not care how new the car is
• "A cheap front toe adjustment is enough." On a car with independent rear suspension, it often is not

How to keep your alignment right for longer

You cannot make alignment permanent, but you can slow the rate at which it drifts.

• Slow down for potholes rather than braking hard on top of them. Braking loads the front suspension just as it takes the impact
• Give kerbs a wide berth when parking. The wheel rim and the alignment both suffer
• Take speed bumps squarely and slowly
• Keep tyre pressures correct. Under inflated tyres deform more under load, which changes the effective geometry
• Distribute loads evenly rather than always loading one side of the boot
• Have the alignment checked when you buy tyres, before the new ones start wearing

Kerb strikes tend to leave evidence on the wheels as well as in the geometry. If the rim is scuffed or the paint has been taken back to bare metal, a mobile alloy wheel repair will restore the finish at your home or workplace, and factory diamond cut wheels can be machined back to their original turned face rather than being painted over.