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Just for the record
Page 90
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Tyres account for 15 per cent of running costs, so DunlopS free tyre record system must make sense, as Bill Brock reports
THE MODERN lorry tyre has been developed to give a high mileage life for a variety of uses ranging from stop-start town work to constant high speed motorway running.
Nevertheless they are subjected to abuse and to get the best performance and maximum life regular maintenance and inspection are essential.
On a mileage cost basis, recent comparisons have shown that tyres may be equated with other major vehicle components and represent a substantial share of the overall vehicle running costs. But few operators consider it worthwhile to keep a check on the performance of individual covers.
The full retail price for a set of 14 tyres to fit a 32-ton tractive unit and trailer could cost as much as £2800 and over a life of 50,000 miles, the cost works out at 5.6p per mile. Different systems of accounting can produce a wide variation in the actual cost per mile.
Thankfully, for the operator, few tyres are purchased at the full retail price, as most carry some kind of discount.
A more realistic assessment of the situation would include a discount of up to 30 per cent. With a 70 per cent casing acceptance, including the cost of retreading, and assuming a total life of 95,000 miles, the cost is reduced to 2.87p per mile.
Commercial Motor's Tables of Operating Costs quote fuel, an area in which most vehicle operators look to save money, at 10p per mile. Tyres are equal to just over one quarter of this expenditure and is estimated at 1 5 per cent of overall running costs under normal operating conditions.
Collectively, however, three factors could reduce tyre life and increase this cost by almost one third -equivalent to almost 1500 for a vehicle averaging 50,000 miles per year.
The right pressure
Efficient maintenance is the key to keeping running costs to a minimum. From surveys carried out by Dunlop tyre service engineers, involving more than 100,000 tyres. it has been shown that more than 25 per cent of all tyres examined were under-inflated by more than ten per cent.
Low inflation is a major factor in premature tyre failure, and the survey engineers concluded that the problem is becoming worse.
The effects of incorrect inflation may be easily spotted if regular inspections are made. On single wheels the shoulder may wear rapidly or the tread may show uneven wear across its width. One under-inflated tyre on twin wheels will deteriorate more rapidly due to scrubbing, while the other will also suffer because of the increased load imposed upon it.
Vehicle overloading will also accelerate tyre wear and the problem becomes more acute with under-inflation. A continuous and high degree of side wall deflection will cause a heat build-up and, if allowed to go unchecked, eventual overheating and consequential failure. A soft tyre is also more susceptible to impact damage.
Excessive speed will also lead to heat build up and deterioration of the tyre.
Pairing part-worn tyres must be made with care to avoid overloading. The tread depth should not exceed 5mm variation nor the overall diameter exceed 1 Omm. Mixing in a regrooved tyre having a similar tread depth could be mis matched by as much as 17mm if the diameters were not compared first.
Regular inspection
Regular inspection will obviate the more serious faults, such as cuts, bulges or stones trapped either in the tread or between twinned wheel combinations, which would otherwise lead to failure in service or a GV9.
Failure to comply with the Construction and Use Regulations relating to tyre usage can result in a hefty fine for each offence, and might easily be more than one per tyre. Periodical checks of inflation pressure, valves and dust caps, tread depth, alignment, and the general state of wear are therefore essential.
Take it easy
The way in which the vehicle is driven can also contribute to the rate of tyre wear — harsh braking, violent acceleration or cornering are to be avoided if maximum life is to be expected.
Modern power-assisted steering makes it possible to apply full lock while the vehicle remains stationary. With as much as three tons spread over the contact area, the resultant massive shearing action which can be imposed upon the chords is to be avoided.
Keeping a check
Dunlop has made a study of tyre maintenance costs and claims that any fleet comprising five vehicles or more will benefit from keeping efficient records. The company has developed a
system, following wellestablished practices, which is offered free.
Most operators are aware of their total tyre costs, but don't maintain individual tyre records because of the cost of keeping them up to date.
Operation of the basic scheme can be made using just two essential forms, a record card and a change tag for each tyre. Collated information can be made to show the total mileage covered by each tyre, the cost per mile (enabling comparisons to be made between different makes), the cost of repair, and the differences between vehicles and/or routes.
Knowledge of the tyre's location on the vehicle at any one time helps to prevent loss. Tyre mileages vary from one wheel position to another.
However, the increased bureaucracy involved in recording movements while a tyre remains on the same vehicle is often considered to outweig any advantage gained and desired this aspect can be ie nored without complicating th final mileage calculation.
To avoid any confusion whe initially using the Tyre Mileag Recording system, it is suge ested that a tyre inventory taken and cards made out fc those already in use.
Accurate cost calculations fc tyres fitted as original equir ment to new vehicles are diff cult to evaluate as the actw cost of individual vehicle con ponents are not generally avai able. If it is ignored altogethE then the mileage figures are th only basis for comparison.
However, if the normal reta price is used, that amour should be deducted from th original vehicle purchase pric so that it is not included twic for accounting purposes.
The vehicle mileometer i normally used to measure th distance travelled. Daily entrie will give especially accurat assessments, but weekly c even monthly readings will no mally be sufficient to allow th total mileage for any tyre failin in the intervening period to b calculated quite closely.
When a tyre is scrapped, th total mileage and cost per mile including repairs, can be calc. lated and the information file for long-term reference. Tyr change tags are a back-up fc the main record card.
If a replacement is made wit the vehicle in service, the ta can be attached to the whet removed complete with all th relevant information. It is also good idea to attach tags to stoc wheels so that they can b returned to the tyre records cler each time a tyre is taken fror stock, transferred from the spar wheel carrier to running positio and vice versa, or returned t the store in either a usable damaged or worn-out conditior
Get it right
As with any record system, i is only as good as the peop1( who operate it. It will only be o use and give a guide to where reductions in running costs car be made if all the necessar) information is included correct') which means it must be kept ur to date on a regular basis.