Tyres are the only part of the truck which directly links the vehicle to the road. For such a major component its maintenance is relatively straightforward, but can often be overlooked.
Paying attention to a few small things can have a tremendous impact on the life and performance of tyres, says Michelin’s New Zealand importer, Tyreline Distributors.
According to Tyreline, choosing the right tyre for the job is important and it recommends that buyers:
Select tyre and fitment according to the type of vehicle and operating requirements, whether for replacement or when specifying new fleet vehicles.
If appropriate, seek out tyres that are regroovable or retreadable as this may help to get longer life out of the case, reducing the cost per kilometre.
Ensure tyres are fitted on the correct size rim or wheel. A trained technician should be mounting the tyre, using the proper tools and lubrication.
Inflate the tyres in relation to the load per axle. Invest in a pressure gauge for checking tyres more easily.
Regularly monitor wear and the general condition of tyres (tread pattern, sidewall, wheels, etc.) as well as the inflation pressure.
Impact of inflation pressure on tyre performance
The most critical factor in tyre maintenance is proper inflation. No tyre or tube is completely resistant to air pressure loss so it’s important to check each tyre regularly.
The tyre pressure has a direct impact on tyre performance; tread life, tyre longevity, vehicle handling, braking and fuel efficiency.
A steer tyre that is running under-inflated by 20% will see the tread life reducing by 17%. Expand that to each tyre across a fleet and the costs quickly stack up.
The tyre is the only component in contact with both vehicle and ground – making proper inflation pressures that are relevant to the load, speed and conditions of use essential, to provide safe operation and maximise performance potential.
Failure to maintain correct tyre pressure can result in sudden tyre destruction and improper vehicle handling. Maintaining proper air pressure also ensures the correct footprint for given load conditions, which help minimise irregular wear.
Air pressure should be checked at least once a week, including spares, before driving off, when tyres are still at ambient temperature.
Checking tyre pressure when the tyres are warm or hot, will show the pressure will be higher than if checked cold. Never bleed pressure from hot tyres, as the tyre will then be under-inflated.
Under-inflation
Under-inflation causes abnormal tyre deflection, which builds up heat and leads to the deterioration of internal components of the tyre. This deterioration can destroy the tyres’ air tightness, and result in a blowout or rapid air loss.
Most blowouts are caused by too little air pressure allowing the tyre to flex beyond its limits, building heat inside the tyre until it overheats to the point where the rubber loses its bond to the internal fabric and steel cord reinforcement.
Under-Inflation also generates abnormal tyre wear similar to the rim being too wide and decreases tyre longevity due to uneven wear.
A tyre that is under-inflated causes the casing ply to over-flex which can lead to a rupture of the casing and subsequent rapid air loss. This condition is known as a zipper rupture.
To prevent this serious issue, Tyreline Distributors technical representative Stephen Lyons recommends following two simple maintenance rules when inspecting tyres:
Any tyre that is four psi (.28bar) or lower than recommended pressure should be checked thoroughly for penetrations, valve leakage or wheel damage which may account for the pressure loss.
Any tyre that has run 20% below the recommended pressure should be considered flat. The tyre should be removed and demounted for complete inspection of the interior. If signs of flat running are present, the tyre should be scrapped.
“By avoiding under-inflation in your fleet, you’ll also avoid reduced tread life, reduced casing life, and reduced fuel economy – which will save you money,” says Lyons.
He says proper inflation will allow the correct tyre profile for full contact with the road promoting traction, braking capability, durability and safety.
Over-inflation
Over-inflation causes tyres to run hard and be more vulnerable to impacts and also generates abnormal wear similar to the rim being too narrow.
As well as this, over-inflated tyres have reduced comfort and grip and decreased tyre longevity, due to uneven wear. Over-inflation also causes extra cable stretching and oxidation which can lead to casing rupture.
The main consequence of over-inflation on truck and bus tyres is extreme cable tension, which increases the chance and severity of fatigue and impact damage to the casing. Prolonged use of over- inflated tyres will cause irreversible degradation, and can result in an unpredictable rapid air loss condition.
Twinning of tyres
To avoid abnormal wear and unequal weight distribution across the tyres, it is essential to ensure the twinned tyres are the same size, manufacturer and tread pattern says Tyreline.
Tyres should be operating within 10 PSI of each other. Tread depth of twinned tyres should also be within 4mm of each other. Mismatched pressure in dual position will cause the tyres to rotate at different revolutions per kilometre resulting in irregular wear and tyre damage.
