PLANNING FOR THE UNPREDICTABLE
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A tyre blowout is always serious: at best it leads to expensive downtime — at worst it can cause a crash. Associated Tyre Services aims to minimise the risks.
• Tyres remain, with windscreens, one of the only two components on a commercial vehicle whose life is unpredictable. Although tyre failure can stop a vehicle in its tracks, the rate of failure, and the hassle involved in getting a vehicle rolling again, can be minimised by careful management.
To find out what precautions can be taken we visited a company that often picks up the pieces and gets a vehicle back on the road: Associated Tyre Services.
Although ATS is often seen on the motorway hard shoulder, the vast majority of its work is done at operators' premises. Perhaps the most vital job handled by visiting ATS personnel is an inspection to try to predict which tyres will fail.
The most common reason for a tyre to blow out is if the side wall is ruptured or split. A 20mm split.in a side wall can wreck a tyre if it is deep enough to reach the cords, as water will enter the crack, freeze and rupture the sidewall, so causing a blowout.
Discarding an expensive tyre on the strength of such a small split is enough to make an operator weep, but to run such a tyre till it fails is inevitably more expensive. For a start, there is no call out charge when ATS visits a workshop. As with all forms of vehicle maintenance, the best work is done in the workshop, not on the side of the road, and regular fleet checks are a large part of its workload.
• Bound to fail
However careful an operator is with its tyre care, sooner or later a tyre is bound to fail on the road. The commonest way that both cost and delay are increased is by the driver phoning in the wrong tyre size: ATS recommends that the size and rating of every tyre fitted to each vehicle is recorded prominently in the cab — it is all too easy to misread the writing on the sidewall on a dark and rainy roadside. The tyre rating is just as important as the size, so everything on the sidewall must be written down.
Although ATS will replace a tyre on the roadside, it will never repair a tyre. Before a tyre is replaced, there can be problems with removing the wheel, particularly if it is alloy. To withdraw reluctant wheels ATS uses, and markets, a puller which can be used with two or three legs. Another problem found with alloy wheels is porosity, which can be cured with paint inside the rim.
To prevent the wheel from seizing on its hub, Copperslip grease is applied to the hub before the wheel is refitted. ATS operatives also carry six different types of wheel nut, and replace worn fasteners.
Another problem that has arisen is the inaccessibility of the inside valve where low-profile tyres are used. The deeper dish of these wheels makes the inner valve even less likely to be checked regularly. ATS markets a flexible valve extension to bring the valve within easy reach of the airline.
Fitting tyres is a specialist job that can eve a lot of aggravation to the untrained. The value of training is shown by Owen McDonald, a fitter with ATS, who has passed his advanced City and Guilds, and can change a tyre in 20 to 25 minutes. Lubrication is essential if the tyre is to be fitted with anything approaching ease, and ATS use a lubricant made by Pang.
To break the bead, McDonald prefers to use a conventional slide hammer bead breaker, although for really stubborn tyres, and tyres fitted to vehicles like earth movers, he carries a powered bead breaker on his vehicle. Broken and lubricated, the bead can be levered over the rim flange once the bead opposite where the levers are inserted has been pushed deep into the rim well.
• Having the knack
There is no other area of vehicle maintenance where having the knack plays so great a part in saving time and temper as changing tyres. For those without the knack, however, there are machines available to save sweat and time.
One such machine is the DCTM Boxer 26 Dunlop Garage Equipment tyre remover. Using both electric and hydraulic power, it will cope with tyres up to 1,550mm diameter, and 700mm width. A combination disc and hook tool is used for bead breaking, mounting and demounting the tyre. The control unit is portable, allowing the operator to work from anywhere around the machine. For operators needing to remove tyres from wheels as large as those used on tractors and earth removers, Dunlop Garage Equipment produce the Boxer 52, which will cope with wheels up to 2,300nun diameter and 915mm width.
Hofmann is another company marketing a CV tyre remover. The Monty 42 uses a pneumatic bead-breaking shovel to remove the tyre and, like the Dunlop machine, it holds the wheel vertically with four clamping jaws to minimise the amount of effort required. McDonald reckons that he can change a tyre with levers in the time it takes to set up a machine to do the same job, but that is more a measure of his skill than the time taken by the machine. He will admit that once a machine has been set up for a particular size of wheel, tyres of that size will be changed faster than can be managed manually.
One job that can really be effectively done by a machine is balancing the wheel. Although universal on cars, wheel balancing has only recently become widespread on trucks. The lead in the commercial vehicle sector came from high-speed bus operators, whose customers demand smooth vehicles.
Much more than just smooth running is gained from balanced wheels. What is felt by the driver as a trembling steering wheel is a wheel thrashing about and placing tremendous strain and wear on both the steering and suspension, never mind what else may be shaken loose in the mean time. An imbalance of grammes when stationary will become kilos or even tonnes when moving fast.
• Balance the wheel
The Hofmann Finishbalancer LPi machine will balance the wheel while it is still on the vehicle, and is easily operated by one man. It works using an infra-red beam, and the imbalance is shown on a digital display. Hofmann claims that the wheel can be balanced with a single spin operation. For balancing drive wheels the operator runs up the wheels with the vehicle's engine and takes the data from a small remote handset.
Most operators, however, ATS among them, will only balance the front wheels on a CV as it is the steering that wears badly with out-of-balance wheels. ms charges 212.50 to balance a front wheel, plus the cost of the weights.
Dunlop Garage Equipment's DWB500 also balances the wheel on the axle, but uses a stroboscopic lamp to "freeze" the spinning wheel. Running off three-phase electricity, it comes complete with axle stands, and is claimed to balance the wheels on any size of vehicle.
Tyres may be the unpredictable element of truck operation, and as such the accountant's nightmare, but steps can be taken to minimise the risk of failure.
A survey recently conducted at a service station revealed that a large proportion of vehicles are running with tyres significantly below the recommended pressure. These tyres will run hotter and wear faster than intended, and will ultimately fail sooner.
By maintaining correct pressures making regular inspections and discarding damaged tyres, however much tread is left, tyre failure will be minimised.
0 by Richard Longworth, Commercial Motor's Workshop technical writer.