Wheel Balance, Wheel Alignment and Safe Driving
Introduction to wheel balancing and wheel alignment
Road Safety authorities have given much attention to vehicle maintenance and aspects such as tyre safety. Vehicle factors are contributing factors to road crashes - and we would like to advise vehicle owners and drivers to pay close attention to their vehicles and vehicle components. This will allow them the best possible chance to arrive safely at their destination!
Aspects often neglected by vehicle owners are wheel balancing and wheel alignment. Most often these aspects are confused and little attention is given to their importance. They contribute towards tyre life, and are both important for your safety on the road!
Wheel balancing allows the tires and wheels to spin without causing any vibrations. This is accomplished by checking for any heavy spots on the wheel-tire combination and compensating for it by placing a measured lead weight on the opposite site of the wheel from where the heavy spot is.
Wheel alignment consists of adjusting the angles of the wheels so that they are perpendicular to the ground and parallel to each other. The purpose of these adjustments is maximum tire life and a vehicle that tracks straight and true when driving along a straight and level road.
In this section we would like to provide greater insight to the importance of wheel balancing and wheel alignment as requirements for safe driving.
Wheel Balance and Safe Driving
When replacing your tyres you will often also have the wheels balanced. But what is wheel balancing?
Wheel balance refers to the even distribution of weight around a revolving tyre and wheel assembly. It ensures that the unit which comprises a wheel rim and a tyre is in balance. Both these units have high and low spots, or heavy and light areas. The first part of getting the complete unit of rim and tyre in balance is to match the heavy areas of one to the light areas of the other.
The next part is to add compensating weight to the complete unit’s light areas so that it rotates perfectly. Wheels are balanced with small counter weights to prevent them from having heavy spots that can cause vibration and premature wearing of tyres, struts, shocks and other steering and suspension components.
When driving with an out-of-balance wheel, the wheel literally bounces down the road or wobbles from side-to-side. The ride disturbance due to unbalance usually increases with speed.
Motoring experts believe that two motoring trends - lightweight suspension systems and responsive lower profile tyres - make it all the more important to have wheels correctly balanced, since these are more sensitive to imbalance than on older heavier cars.
International experts have revealed that at 60 mph, your wheel is subjected to a pounding force of 60 lbs if your wheel is only 6 oz. out of balance! Half an ounce of uneven weight distribution is already enough for vibrations and noise problems to become noticeable.
Dangers of unbalanced wheels
Even if we know what wheel balancing means – do we know why it is dangerous to drive with wheels that are not balanced?
We would like to reflect on the dangers of driving with unbalanced wheels:
- Wheels that are not balanced or are out of balance generally produce a vibration that is uncomfortable to drive in and negatively affects the handling of the vehicle.
- Unbalanced wheels place severe stresses and strains on the wheel bearings and suspension components.
- Steering components can also be damaged and all the parts may fail prematurely in extreme cases.
- Unbalanced wheels result in premature wearing of suspension and steering components, rotating parts and tyres.
- Unbalanced wheels increase the need for additional energy and increase fuel consumption.
- Ignoring the symptoms can be dangerous and expensive.
Wheel Balancing – what do we need to know?
It is important that we are able to detect when wheels might be out of balance.
The symptoms of a wheel that is out of balance are:
- Vibration in the steering wheel at certain highway speeds.
- Vibration in the seat or floorboard at certain highway speeds.
- Scalloped or cupped wear pattern on the tires
The first sign that wheels may be out of balance is when the steering wheel starts to wobble above a certain speed. The light weight of modern cars means that they don't dampen down the vibrations caused by spinning wheels in the way that older, heavier vehicles could.
Wheel balancing will ensure a smoother ride and more enjoyable driving. The better wear from the tyres will also save you time and money.
Tyre Safety experts should be able to pay attention to the static and dynamic balance of your tyres. Herewith a very brief description:
- Static balance
Static balance can be measured by a static balancing machine where the tire is placed in its vertical axis on a non-rotating spindle tool. The spot on the tire where the mass is greatest is acted on by gravity to deflect the tooling downward. The amount of deflection indicates the magnitude of the unbalance. The angle of the deflection indicates the angular location of the unbalance. Dynamic balance
- Dynamic balance
This describes the forces generated by asymmetric mass distribution when the tire is rotated, usually at a high speed. In the tire factory the tire is mounted on a balancing machine test wheel, the assembly is accelerated up to a speed of 300 RPM or higher, and sensors measure the forces of unbalance as the tire rotates. These forces are resolved into static and couple values for the inner and outer planes of the wheel, and compared to the unbalance tolerance (the maximum allowable manufacturing limits).
Advice when you balance your wheels:
- Wheels should always be balanced off the car, as the modern wheel balancer does both Dynamic and Static Balance at the same time.
- If you experience an out of balance condition on the steering, have ALL the wheels balanced, and not merely the front wheels. Unbalanced wheels on the rear can often be felt through the steering.
Wheel Alignment and Safe Driving
Most of us will refer to wheel alignment when we mention tyre wear and wear patterns. There are however even more important reasons why wheel alignment is important for safe driving and road safety.
These include the need to reduce stresses and strains on the vehicle suspension components and improve the handling of the vehicle.
What is wheel alignment?
Wheel alignment is the process whereby the wheels are aligned to point in line with the direction of rotation. This is done to ensure that the tires are calibrated to 'point' straight ahead. Proper wheel alignment makes a vehicle steer easily and allows tires to wear evenly.
Deteriorating roads contribute to a greater need for regular wheel alignment. Tires can be nudged out of alignment by accidentally hitting them against objects such as curbs and parking blocks, or by catching a centre cement divider while making a miscalculated turn.
Once a tire is knocked out of alignment, its orientation on the vehicle is slightly off-centre. The degree of misalignment is not obvious to the human eye, but the effects will be noticeable on your ability to steer the vehicle.
During wheel alignment there are three major considerations. These are
- camber (vertical angle)
- caster (rearward inclination)
- toe (front of wheels pointing inwards or outwards).
Wheel alignment usually requires that adjustments are made to various parts of the suspension. Alignment angles can also be altered beyond the maker's specifications to obtain a specific handling characteristic. Motorsport and off-road applications may call for angles to be adjusted well beyond "normal" for a variety of reasons.
We would like to provide a brief explanation of the settings used in alignment. Even though this is a bit technical –it will provide some insight to the expertise required from tyre experts when aligning your wheels:
- Toe Settings – this is the inward or outward pointing of the wheels in relation to the centre line of the vehicle, and is set to take up any slack in suspension joints so that the tyres will in fact run parallel with one another when the vehicle is travelling in a straight line. Too much toe will dramatically reduce tyre life. The modern vehicle has much tighter tolerances than cars of yesteryear so the settings are far less than they were.
- Camber – this is the tilt away from the vertical of the wheel and is designed to place the wheel loading on the larger inner wheel bearing of the front wheel on rear wheel drive vehicles. Too much camber will cause a tyre to wear off on the shoulder, and differing camber angles from one side to another will cause the vehicle to pull to one side.
- Caster – the backward tilt of the steering axis, and is designed to give feel on the steering as well as provide steering self-centring, so the steering comes back to the straight ahead following a corner. Too little caster will cause the vehicle to wander, and too much will cause heavy steering.
- Steering Set Back – this is where one wheel is ‘set back’ from the other. If a vehicle has a high steering set back, the vehicle will pull toward the side where the wheel is ‘set back’. This can often occur when a vehicle has been involved in an accident.
- Steering Axis Inclination – this is the tilt from the vertical of the steering axis, and is designed to create a vertical load through the axis, in order to reduce stresses and bending moments on suspension components.
- Thrust Angle – this is where the rear wheels are out of line with those on the front, and the vehicle will have a tendency to ‘crab’. Again, this can occur when a vehicle has been involved in an accident.
- Scrub Radius – this is the radius created between the centre line of the wheel in contact with the road surface and the line drawn through the steering axis. This can either be positive where the wheel positioning is on the outside of the steering axis line, or negative where the wheel positioning is inside the steering axis. Scrub radius may also be referred to as Roll Radius. Changing the offset of the wheels on the vehicle will change the scrub radius and could severely affect suspension component life, due to increased stresses being placed on them.
Dangers of wheels that are not aligned
What are the symptoms of a car where the vehicles are not aligned – and why are they a road safety risk?
The symptoms and dangers of a car that is out of alignment are:
- Wheels that are not aligned will compromise your safety and the ability to steer the vehicle.
- Out-of-alignment of a car will result in the vehicle continuously drifting or pulling to one side of the road when you let go of the wheel.
- If the wheels aren’t going in a straight line it means the tyres will be dragging sideways to some extent - Pulling or drifting away from a straight line.
- This is not only annoying, but the tire that is out of alignment will also wear prematurely and unevenly because of the constant drag placed on its tread.
- As the tread wears away the ability for the tyre to grip wears away with equal rapidity.
- The drag can also impact on fuel consumption.
- Braking, handling, the ability to react to steering input or any form of evasive action becomes compromised.
- This is especially important when the driver has to respond swiftly and change course in an emergency situation.
What do we need to know about wheel alignment and safety?
It is important to be alert to the warning signs that the wheels might be out of alignment. Uneven tread wear is a sign that the car was driven quite a while with improper wheel alignment. Often, the inner tire tread will wear down smooth while there is still plenty of outer tread left, or visa-versa. The result is that tires have to be replaced sooner rather than later.
Your driving behaviour will decide how often your vehicle requires wheel alignment. In order to preserve the wheel alignment on a vehicle, avoid pot holes, climbing curbs, and parking up against curbs. If you have to climb a curb, do it very slowly and at a slight angle.
When do I need to consider wheel alignment?
Alignment should be checked every 10,000 km or 6 months, whichever occurs first, unless you know that you have hit a pothole, or some other object, in which case it should be done immediately as a precaution.
Other facts drivers should know about wheel alignments:
- A proper wheel alignment should best start and end with a test drive.
- The front end and steering linkage should be checked for wear before performing an alignment.
- The tires should all be in good shape with even wear patterns.
- If you have a tire with excessive camber wear, for instance, and you correct the alignment problem that caused that wear, the tire will now be making only partial contact with the road
- Pulling problems are not always related to wheel alignment. Problems with tires (especially unequal air pressure), brakes and power steering can also be responsible.
How is wheel alignment performed?
A camera unit (sometimes called a "head") is usually attached to a specially designed clamp which holds on to a wheel. There are usually four camera units in a wheel alignment system (a camera unit for each wheel). The camera units communicate their physical positioning with respect to other camera units to a central computer which calculates and displays how much the camber, toe and caster are misaligned.
Often with alignment equipment, these "heads" can be a large precision reflector. In this case, the alignment "tower" contains the cameras as well as arrays of LEDs. This system flashes one array of LEDs for each reflector whilst a camera centrally located in the LED array "looks for" an image of the reflectors patterned face. These cameras perform the same function as the other style of alignment equipment, yet alleviate numerous issues prone to relocating a heavy precision camera assembly on each vehicle serviced.
More attention should be given to wheels and tyres as requirements for safe driving. Tyres are the only components which keeps your vehicle in contact, physically, with the road surface. They allow you to start, stop and change direction.
If we compromise their ability to do these basic functions we are putting ourselves and all road users at risk. Neglecting wheel alignment and balancing on our deteriorating roads is a definite road safety concern.
The Arrive Alive website would like to suggest that vehicle owners have their wheel balance and wheel alignment checked periodically by a professional from the tyre industry. This should normally take less than an hour - and the benefits would be priceless!!