Most of us appreciate and follow manufacturer recommendations regarding vehicle maintenance, but are we as disciplined when it comes to tyre pressures and rotation, or wheel balancing and alignment?
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Ensuring that an internal combustion engine operates at its best and remains reliable requires the use of specified engine oil and fuel, as well as strict adherence to a detailed maintenance schedule.
However, properly maintaining a vehicle involves more than just regular oil changes and engine checks; it also requires proper maintenance of the tyres and wheels, which includes regular checks on tyre pressure, wheel balancing, tyre rotation and wheel alignment. A vehicle suspension system is a lot more complicated than many realise. In addition to the basic design, extensive development goes into optimising the geometry, tuning of bushes, spring rates, shock absorber calibration, tyre selection and other parameters. These all influence vehicle dynamic performance including steering response, directional stability, handling, ride quality, braking and road noise. Maintaining these items within specification is key to achieving the best levels of vehicle and ultimately, safety. While some of these checks are included in the regular vehicle service schedule, others remain the responsibility of the driver as they need to be checked more frequent investigation; for example after heavy rough-road use or accidentally hitting a pothole or kerb. Neglecting these regular checks can lead to a range of problems, from compromised vehicle dynamics and reduced fuel efficiency to catastrophic tyre failure. The following is an in-depth exploration of the importance of each of these maintenance tasks and the potential consequences of neglecting them.
Tyre pressures
Maintaining correct tyre pressures is critical to ensuring optimal tyre contact with the road, which is crucial for safety, as well as fuel consumption and tyre life. Fortunately, it is also one of the simplest maintenance tasks because it can be carried out in a fuel station while the car is being refuelled. The general recommendation is that tyres are checked at least once per month, and always before a long trip, or when carrying a heavier-than-usual load. Visual checks are useful for detecting obvious damage or a deflated tyre, but should not replace a proper pressure check. Neither a low-profile performance tyre, nor an on/offroad 4×4 tyre with its tall but reinforced sidewall appears much different to normal when inflated to 50 kPa below specification.
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Manufacturer pressure recommendations, which are usually found on a sticker conveniently placed in the frame of the driver’s door, will show pressures for lightly laden, everyday use and higher pressures for fully laden or high-speed driving. Pressures should always be checked when the tyres are cold – ideally driven less than 2 km. Checking hot tyres during a long-distance trip should be avoided. If they were correctly set before the trip, they should not require a pressure check unless the driver has noticed the vehicle starting to pull to one side, particularly when braking or the handling feels different (e.g. not as responsive to steering input, particularly in one direction). In this situation, a visual check while also touching the back of one’s fingers against the shoulder of each tyre to check temperature should indicate whether a tyre has lost pressure. If pressures must be checked when tyres are hot, it should be done to compare pressures and detect whether one tyre has lost pressure, rather than setting pressures.
Underinflation is one of the leading causes of tyre failure, as tyres experience excessive heat buildup due to friction, leading to tread separation, failure of the tyre structure and ultimately a blowout. Interestingly, many who have experienced a blowout regard it as an inherent defect or “out of the blue” failure of the tyre, when in fact it was because of low tyre pressure. The increased rolling resistance will also increase fuel consumption while braking, handling and wear will be negatively affected by the uneven load distribution across the tyre tread. Overinflation changes the shape of the tyre, reducing the size of the contact patch, resulting in less grip, compromised ride quality and increased wear, particularly in the centre of the tread.
Tyre rotation
Tyres experience different loads and wear patterns depending on where they are fitted on a vehicle. This is most prevalent on an FWD vehicle, where the front tyres are required to cope with steering, and most of the braking and vehicle weight, while transmitting power to the road. This results in a much higher rate of wear than the rear tyres. RWD vehicles exhibit more even wear rates but different wear patterns, as the front tyres handle the steering and most of the braking, while the rear tyres handle the power transmission.
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Rotating tyres at regular intervals helps achieve uniform wear across all tyres, extending their lifespans. Most manufacturers recommend tyre rotation intervals in vehicle owner manuals and specify how the tyres need to be rotated as this differs between FWD and RWD/AWD vehicles. Care needs to be taken that asymmetrical or unidirectional tyres, marked with an arrow alongside the word “outside” or “rotation” on the sidewall – remain on the same side of the vehicle, as the tread design only permits rotation in one direction. Tyres with wider grooves and gaps between tread blocks, such as 4×4 tyres designed for muddy conditions, can be prone to a heel-and-toe wear pattern due to distortion of the tread blocks under acceleration and braking. This is entirely normal and can be managed by regular rotation before the wear patterns become excessive.
Wheel balancing
Tyres, which comprise a complex assembly of beads, belts, plies, sidewalls, and tread before being moulded, are manufactured to the tightest tolerances, but will inevitably still require some fine balancing. This is done by placing small weights on the wheel rim to counterbalance any heavy spots and ensure a smooth and comfortable ride. It also avoids uneven tyre wear and the excessive wear of steering and suspension components. Balancing should be carried out whenever a wheel shake or vibration develops, and whenever new tyres are fitted.
Wheel alignment
Wheel alignment specifically refers to the alignment of the wheels in the direction of travel (longitudinally) but is also broadly used as a general term referring to the wheel geometry including camber and caster. Proper alignment to manufacturer specifications is crucial for vehicle dynamic performance, including directional stability, steering, braking, and handling, as well as fuel efficiency and tyre wear.
Wheel alignment is measured as toe-in and toe-out. When viewed from above, it is a measure of how much the leading edge of the wheels on the same axle, point toward or away from each other. Slight toe-in improves directional stability, but an excess creates uneven tyre wear while increasing drag and fuel consumption.
Camber is a measure of the inward or outward tilt of the top of the wheels when viewed from the front. Slight negative camber (top of wheels tilted inward) improves grip when cornering as it helps maintain the tyre contact patch, compensating for body roll. Excessive camber can also lead to premature wear of the inside of the tyre tread.
Caster is a measure of the difference between the angle of the steering’s rotational axis and the vertical axis, through the centre of the wheel, when viewed from the side. Road cars are designed with positive caster, meaning that on vehicles with front struts, the upper strut mounting is rearwards of the lower ball joint and on vehicles with upper and lower wishbones, the upper wishbone ball joint is rearwards of the lower wishbone ball joint. Positive caster causes the front wheels to align with the direction of travel, providing steering self-centring and increasing straight-line stability.
Front alignment can be adjusted by turning the threaded body of the tie rod end, which links the front hub and the steering rack, to increase or reduce its length. It needs to be done on both sides to ensure the same alignment of each wheel relative to the vehicle’s centre line or the steering will pull to one side. On many cars front camber and caster are not adjustable, but with some suspension designs, shims and eccentric washers allow limited adjustment. Rear alignment and camber are not adjustable on a vehicle fitted with a solid axle, but with independent suspension eccentric washers or shims are used on some of the links, allowing a limited degree of adjustment.
Regularly checking and maintaining tyre pressures, rotating tyres, balancing wheels and checking alignment are essential to ensuring the safety, performance, and longevity of a vehicle. These tasks are relatively simple and inexpensive compared to the potential costs and risks associated with neglecting them. Incorporating these checks into regular vehicle maintenance routines will provide drivers with a smoother, safer, and more economical driving experience.
Find the full feature in the August issue of CAR Magazine.
