A wheel alignment sets the angles at which your wheels meet the road, within tolerances measured in fractions of a degree. Symptoms include pulling to one side, an off center steering wheel, and uneven tire wear. Pothole impacts and curb contact are the usual causes in city driving.
What angles does a wheel alignment adjust?
Alignment sounds like a single adjustment. It is actually three distinct angles, each
affecting behavior differently, and each adjustable within a narrow tolerance.
Toe
Whether the wheels point slightly inward or outward when viewed from above. Toe is the
angle most easily disturbed and the one that destroys tires fastest. A wheel pointing even
slightly away from the direction of travel is scrubbed sideways across the road surface every
meter the car moves.
Camber
The inward or outward lean of the wheel viewed from the front. Excessive camber wears one
shoulder of the tire and reduces the contact patch available for braking and cornering. Uneven
camber between the two sides pulls the car toward the more positive side.
Caster
The tilt of the steering axis viewed from the side. Caster provides straight line stability
and the self centring action that returns the wheel after a turn. It affects steering feel more
than tire wear, and unequal caster produces a pull that is often mistaken for a brake fault.
What are the symptoms of a wheel alignment problem?
- The vehicle pulls to one side on a flat road with hands lightly on the
wheel. Note that road camber alone causes a slight drift to the right on most roads, so judge
this where the surface is level. - The steering wheel sits off center while the car tracks straight. This is
the clearest single indicator and the one most people notice first. - Uneven tire wear, particularly a feathered edge across the tread blocks
or wear concentrated on one shoulder. - Vague or wandering steering requiring constant small corrections.
- The wheel not returning to center smoothly after a turn.
A vibration is usually a balance or bent wheel problem rather than alignment, though a hard
impact frequently causes both at once.
What knocks wheel alignment out in city driving?
Alignment angles are held by suspension geometry, and anything that deflects a component
changes them. In a dense city the opportunities are constant.
Potholes are the obvious cause, particularly square edged holes struck at speed, where the
load passes through the tire into the wheel and then into the suspension. Curb contact while
parallel parking is the underrated one, because the impact is often slow enough to feel
harmless while still applying a substantial lateral load directly to the wheel.
Wear contributes too. Bushings, tie rod ends, and ball joints develop play over time, and
once there is play the geometry moves under load even if the static measurement looks
acceptable. This is why an alignment on a vehicle with worn components does not hold, and why
a competent shop inspects for play before adjusting anything.
What can tire wear patterns tell me about alignment?
Tires record alignment faults, and the pattern identifies the angle responsible.
- Both shoulders worn, center fine. Underinflation rather than alignment.
- Center worn, shoulders fine. Overinflation.
- One shoulder only. Camber.
- Feathered edges across the tread blocks, smooth one way and sharp the
other when a hand is run across them. Toe. - Patchy or cupped wear. Usually worn dampers or an imbalance rather than
alignment.
Checking this takes seconds and is worth doing whenever tire pressures are checked, because
a pattern caught early costs an alignment while the same pattern caught late costs tires as
well.
What is the difference between two wheel and four wheel alignment?
Shops offer alignments at different prices, and the difference is usually how many wheels
are measured and adjusted.
A front end or two wheel alignment measures and adjusts the front wheels only. It suits
older vehicles with a solid rear axle where the rear geometry is fixed and cannot be adjusted.
A four wheel alignment measures all four, establishes the rear thrust line, and aligns the
front wheels to that line rather than to the vehicle’s centreline.
That thrust line concept is the part worth understanding. If the rear axle is not pointing
exactly where the body points, the vehicle travels very slightly sideways, which drivers
describe as the car crabbing or the steering wheel sitting off center no matter how often the
front is adjusted. Aligning the front wheels without measuring the rear on such a vehicle
produces a car that tracks straight only by holding the steering wheel crooked.
Most modern vehicles have independent rear suspension with adjustable rear toe, and on
those a four wheel alignment is the correct service. If a quoted price looks unusually low, it
is worth asking which one is being performed, because a two wheel alignment on a car that needs
four will not resolve the complaint that brought it in.
What does a proper wheel alignment involve?
The vehicle goes on a rack with sensors mounted to each wheel, and measured angles are
compared against the manufacturer specification. What separates a good alignment from a poor
one is what happens before the adjustment.
Tire pressures should be set first, since they affect the measurement. Suspension and
steering components should be inspected for play, because adjusting geometry held by a worn
component is temporary at best. Ride height should be checked where it is adjustable or where
sagging springs have altered it, since camber changes with ride height.
Ask for the printout showing before and after figures against specification. That document
tells you what was actually wrong and what was corrected, and a shop that measures properly
will produce it without being asked. After any significant pothole impact an alignment check
is worthwhile even when the car drives normally, because the measurement is quick and the
alternative is discovering the fault through a set of prematurely worn tires.
Frequently asked questions
How often should I get a wheel alignment?
Once a year is a reasonable baseline in city driving, and a wheel alignment check is worthwhile after any hard pothole impact or curb strike, and whenever tires are replaced so the new set does not inherit an existing fault.
Can a wheel alignment fix uneven tire wear?
It stops the wear progressing but cannot restore rubber already lost. A wheel alignment corrects the angle causing the pattern, though a badly worn tire may still need replacing and can remain noisy until it is.
Does a wheel alignment fix a vibration?
Usually not. Vibration generally indicates wheel balance or a bent rim rather than geometry, so a wheel alignment alone will not resolve it, although a single pothole impact often causes both problems at the same time.
Why did my wheel alignment not hold?
Most often because a suspension component has play. A wheel alignment sets angles held by bushings, tie rod ends, and ball joints, and if any of those are worn the geometry shifts under load regardless of the static setting.
Related services
Reference: NHTSA tire safety information.
