Often confused with wheel balancing, a wheel alignment, boiled down to the simplest explanation, is the process of ensuring the angles of the wheels are perpendicular to the ground and all wheels are parallel to each other.
On factory, or close to stock vehicles, the wheel alignment specifications are designed to prolong tyre lifespan, prevent the vehicle from wanting to track to either side, and ensure predictable vehicle handling while accelerating, steering and braking.
Here at Tyre Review, we’re going to run you through everything you’ll need to know about wheel alignments and how they affect your vehicle.
Vehicle suspension is a collective term for arms, bushes, springs and more under your vehicle.
Why do vehicles need wheel alignments?
With any mass produced product, vehicles included, there is a small tolerance for variation from vehicle to vehicle. When the vehicle is designed, there is some adjustment built into the suspension to account for variances as well as suspension components wearing over time.
Why are wheel alignments important?
As mentioned above, wheel alignments are designed to provide predictable and safe handling characteristics to a vehicle. A good wheel alignment will also ensure tyres wear evenly (check back for our in-depth guide to diagnosing types of tyre wear).
A wheel alignment is a great way to fine tune the way your vehicle handles too. In some motorsport applications, the alignment may be set far beyond the factory specifications for that vehicle in order to achieve more performance at the cost of tyre wear or component lifespan, but more on that later.
What’s involved in a wheel alignment?
In all vehicles with suspension, there is a complex relationship between suspension arms, vehicle height and steering angle. Collectively known as ‘suspension geometry’ this mess of mechanical linkages, levers and components is what all comes together to make your vehicle handle the way it does.
Since you’re on the Tyre Review page and looking at wheel alignments, you may have heard of the terms camber, caster and toe.
Camber is the inwards or outwards tilt of the wheels when looked at from the front or behind of a car. Negative camber is where the top of the wheel leans in towards the middle of the vehicle, while positive camber is where the wheel leans away from the car.
Most vehicles from the factory have ever so slight amount of negative camber from the factory (less than 1.5 degrees) so that, as a vehicle ‘leans’ into a corner the outside wheel will be perpendicular to the ground, providing maximum grip and safety.
In the real world, roads are never flat, with most roads having a natural camber so negative camber will help the tyre grip more efficiently in real-world situations. Even on a race track the corners aren’t flat so some amount of camber will provide more grip in almost all situations, this also helps the tyres wear more evenly unless running more aggressive camber and in that case, it will lead to the opposite.
In vehicles with independent suspension, the natural camber of the wheel can change significantly with ride height. A good example of this is lifting or lowering your vehicle with aftermarket suspension (more on that later).
Caster is a measurement that affects the steered wheels on a vehicle. In any vehicle, the steering wheel will move on a pivot. The vertical angle of this pivot, as seen from side on, is referred to as the ‘caster angle’.
In old style cars with solid front axles and ‘kingpins’ on which the steering assembly pivots, the caster was easy to see and visualise. Newer cars aren’t much more difficult, just trace an imaginary line through the upper and lower ball joints on the steering knuckle, or the lower ball point and strut top in a Mcpherson suspension setup.
Looking from the side, if the steering angle leans towards the front of the vehicle, caster is described as negative, if the angle leans towards the rear of the vehicle, caster is described as positive.
The effect of an out-of-spec caster can be dramatic. If the caster is set too far negative, the steering will be very light and the vehicle will ‘wander’ and be tiresome to keep in a straight line, while a caster that is too far positive will result in heavy steering and violent steering wheel jerking over bumps.
On most vehicles, the caster is non adjustable. If the caster is not within specifications, or varies side to side, there is a good chance the vehicle has suffered damage or has worn out suspension components.
Toe measurement is the difference between a pair of wheels being perfectly parallel to the centerline of the vehicle and not. Toe can be measured by comparing the distance between the front of the tyres and the back of the same tyres. Any difference can be described as toe-in or toe-out and is measured in degrees.
Toe is one of, if not the, most important measurement when it comes to vehicle handling and tyre lifespan. Ideally, for maximum tyre lifespan, the toe should be set at, or close to, zero degrees. Excess toe in either direction will result in extremely rapid tyre wear focused on the inner or outer edge of the tread.
In motorsports and performance oriented applications, suspension tuning with toe settings is a great way to fine tune how the vehicle handles in corners.
Fine tuning the toe at either end of the vehicle can have slightly different handling characteristics.
For example, toe out will increase the tendency of a vehicle to be ‘twitchy’ or want to aggressively turn into corners, promoting oversteer.
Toe-in can be added to a vehicle to improve the vehicle's high speed stability in straight lines, making the vehicle less likely to ‘tramline’ although making the steering feel more ‘dull’.
Other components of suspension and wheel alignments
Suspension geometry is an entyre (geddit?) science unto itself and there is much more to a wheel alignment than a simple ‘toe and go’ at your local shop. We’re about to get pretty techy.
Thrust angle is closely related to toe. If you’ve ever followed a vehicle that appears to ‘crab’ down the road on an angle, you’ll have seen what thrust angle that isn’t within specification can do to affect how a vehicle drives.
Thrust angle is where a pair of wheels are out of spec, with one wheel having toe in while the opposite has toe out. This is most often seen on vehicles that have a solid axle that have experienced suspension damage and the whole axle is no longer perfectly perpendicular to the vehicle centerline.
Since the rear axle thrust angle is not adjustable in most vehicles, configuring the rear wheel toe to correct thrust angle is about the only way to get the vehicle to drive straight again.
Steering wheel alignment
Related to toe settings is the steering wheel alignment. If you’ve ever wondered why you get your vehicle back from repair and the steering wheel is no longer straight when you drive along the road. It’s because one steered wheel has toe out, while the other steered wheel has toe in.
To correct a poor steering wheel alignment, the wheel has to be centered from inside the car while the tie-rods need to be adjusted to bring the wheels back to the designed amount of toe in-out.
In Australia, most roads are ‘crowned’ to allow for the runoff of water into gutters and down drains rather than building up on the road surface. If the road is heavily crowned or otherwise cambered, the steering wheel will need to be turned to counter any tendency for the vehicle to want to turn down the slope. This is normal.
If you suspect your vehicle needs a steering wheel alignment, the best place to test it is a large flat carpark or highway. If your wheel isn’t pretty dead nuts on straight while you’re driving in a straight line, it’s worth getting checked out.
Steering Axis Inclination (SAI)
SAI is similar to caster but measured from the front of the vehicle looking backwards. SAI is the difference between the true vertical and the angle of the steering pivot (either through the two ball joints on the steering knuckle, the kingpin, or the ball joint and strut as in McPherson suspension).
The SAI combined with caster can be observed to slightly lift the front of the vehicle up if the steering wheel is turned lock-to-lock at a standstill. It’s this force, along with caster that makes the steering system on a vehicle want to self-centre.
In almost all cases, SAI is not adjustable without changing the wheel camber and some alignment machines are not designed to measure SAI. However, in cases where the steering axis inclination is not equal side to side, the vehicle will noticeably pull to one side at slow speeds. If this is the case, immediately suspect suspension damage or bent components.
Included angle is the Steering Axis Inclination combined with the Camber of that wheel. In a perfect world this is as close to equal on both sides as possible.
Imagine standing in front of the vehicle and drawing an imaginary line through the Steering Angle Inclination until it hits the ground. Now, comparing that mark to where the centerline of your tyre is will give you the scrub radius.
If your tyre centerline is outside of your SAI, you have a positive scrub radius. The inverse is also true, if the tyre centerline is narrower than your SAI plane you have negative scrub radius.
The scrub radius cannot be altered on a vehicle without replacing either the steering knuckle or some other part of the suspension geometry, or an easier option is to replace the wheel with an offset more suitable for the vehicle (we're working on a great article about understanding wheel specifications, stay tuned).
If the scrub radius is too large in a front wheel drive car, unwanted characteristics like torque steer will become apparent, where the vehicle will want to veer off to one side under acceleration.
Positive scrub radius can also have negative effects with braking. Say, if one front brake fails, using the brakes will violently pull the car to the other side.
Lastly, an important factor in the alignment of your vehicle's wheels is the ride height. From the factory, all vehicles are designed to be within a certain range where during normal suspension travel, where the wheels are kept more or less in line with the alignment specifications.
In vehicles with no camber adjustment, raising or lowering may contribute to camber changes which will make it impossible for the wheel alignment to be within factory spec. In this case, the vehicle may be fitted with aftermarket adjustable suspension components that offer more adjustability than the factory items.
Raising or lowering a vehicle past a certain point, which differs across makes and models, causes items like tie rods, which control your toe in on your steered wheels aren’t able to maintain correct alignment as the suspension cycles up and down.
Bump steer is the phenomenon where your wheels turn slightly side-to-side when the suspension travels up and down, such as over a bump, without any steering wheel inputs. From factory, bump steer is more or less completely tuned out of the factory suspension geometry, however raising or lowering your vehicle beyond a certain range can reintroduce this effect.
Typically on a road, bump steer is described as the car becoming jittery and unsettled over bumps and can only be resolved by raising or lowering the vehicle closer to standard height, moving the steering rack (if you’re that committed to the low life, hats off to you) or altering where the tie-rod connects to the knuckle with the use of spacers.
What are the symptoms of a bad wheel alignment?
There are a few things to look out for that may be signs your vehicle's alignment needs attention. The most common is where your vehicle ‘pulls’ to one side or another. This has a few probable causes though, and a flat tyre is the first thing to check. If your tyres are good but your vehicle is still pulling to one side, it’s worth getting your alignment checked out.
If the vehicle was involved in a small accident or hit a gutter there is a chance it's put the alignment heavily out of whack or damaged suspension components.
Uneven tyre wear is another sign your vehicle's suspension needs work. This could be down to a poor alignment or a worn out suspension component like a suspension bushing.
What can negatively affect a wheel alignment?
Typically, a bad wheel alignment can be traced to a few different reasons:
Damage. If you’ve hit a pothole or a curb or have otherwise been in an accident, bent or damaged suspension components can place the wheel slightly out of specification compared to where it ought to be.
Wear and tear. Between every suspension arm and moving part under your vehicle, there are rubber suspension bushings that allow parts to move freely in certain directions but prevent unwanted movement in other axis. As vehicles age and travel more and more kms these bushings will slowly wear out, get softer and eventually give out and tear, allowing the suspension to move in unintended ways.
The great news is that suspension bushings will give a lot of warning signs before they give up the ghost, such as audible clunks or sloppy handling, giving you plenty of time to get your vehicle looked at. Tyre shops will examine something is wrong when they can’t get the car aligned to factory specifications.
Too much payload. If you regularly transport heavy loads in your vehicle, you should aim to get a wheel alignment at the weight you typically drive at, as this is the position your wheels will be spending the most time in. Carrying excessively heavy loads can cause suspension, frame or axle damage, possibly requiring extensive repairs to get the vehicle to run true again.
Modified suspension height. Often if you’ve raised or lowered your vehicle, the ideal suspension geometry has been tweaked and will need to be taken to a shop to attempt to bring the vehicle back into alignment.
Bent or damaged wheels. Since almost all the alignment machines in use rely on target panels to be fixed to each wheel, it stands to reason that if your wheels aren’t straight, your alignment calibration will be off too. It’s easy to check for damaged wheels, if you suspect yours aren’t in great condition, get your local tyre shop to throw them on the wheel balancer and get the runout checked.
How often should a wheel alignment be performed?
Wheel alignments are generally recommended to be performed every time you get new tyres fitted, as well as at roughly 10,000km intervals while you’re getting your tyres rotated.
Having a regular alignment and rotation schedule ensures that you’ll get the most from your tyres and aims to prevent uneven wear.
Contact your local tyre store for a check-up and comprehensive 4 wheel alignment. If your vehicle has been substantially modified you may need to customise or replace other components in your suspension in order to maintain your alignment in the recommended range.