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Tread warily and reduce
Page 91
Page 92
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tyre costs
.Proper inflation ups mpg .Better tread patterns improve safety • Mismatching twins is so expensive
FUTURE TYRE development will depend to a large extent on vehicle development, Mr Barrie Allbert, truck tyre development manager of The Dunlop Rubber Co Ltd, told the conference.
In the next 10 years there was unlikely to be any fundamental change in basic vehicle design, he said.
But he expects that the radial tyre will completely replace the cross-ply and that tubeless radials will become dominant.
Mr Allbert considers that development towards improving the structure and consequently the life of casings will continue. Although the basic design of tyres would remain unaltered, new reinforcing materials would almost certainly be introduced.
He said that as manufacturers of vehicles give more detailed consideration to braking and directional control, they focus attention on the safety aspect of vehicles. This in turn encourages tyre manufacturers to continue to examine and develop tread patterns which will give better grip on wet surfaces.
Research and development of techniques to extent tyre life through improved repair and retreading services would con tinue to occupy more and more of tyre manufacturer's attention. It was conceivable that a tyre/wheel system could be developed which would give the driver satisfactory control in the event of sudden deflation.
He contends that the tyre industry has kept abreast of the technological developments in both vehicle manufacture and motorway construction and at modest price increases. He believes, however, that vehicle• operators can do much to reduce or contain costs by exercising greater control in their daily operation.
It was important to recognise that the performance of a radial tyre is more dependent on correct pressure being maintained than is the case with cross-ply tyres. "Indeed it is for this reason that cross-ply tyres still dominate in many less sophisticated overseas markets," he said.
In a detailed survey in which 58,400 tyres were examined throughout the country between 1974 and 1976, 25 per cent were found to be under-inflated by 10 per cent or more, and 4.5 per cent had mismatched twin assemblies. "Should these statistics not appear to be particularly start
ling,he said, "it is only
necessary to add that 8.7 per cent were completely flat or impossible to check due to incorrect fitment."
Very significant improve ments in fatigue life and a reduction in premature tyre failures could be achieved. Operators should adopt a similar attitude to tyre maintenance as they do to engine maintenance. He illustrated how tyre costs per mile are consistently
continued overleaf
higher than engine costs per mile.
The type of operation on which a vehicle was engaged has a major influence on the life of the tyres. According to Mr Allbert, motorway cruising causes relatively little wear on treads because relatively little force is required to overcome the wind and rolling resistance of the vehicle. Such operation, he says, minimises driving, .braking and cornering forces and tyre life is normally high.
Conversely, vehicles operating continuously in a mountainous area experience large changes in speed and direction -and therefore have a much lower tyre tread life," he said. The difference in tyre life between these two types of operating circumstances could be as large as four to one.
"It should be appreciated that the effect of individual operating factors on tyre life are significantly larger than the influence of the design of the When carrying out experimental comparisons manufacturers ran identical vehicles fitted with different tyres running over the same route and driven in turn by each of the drivers. Tyres were switched periodically between vehicles, but even using this method it was impossible to get an accuracy better than plus or minus 5 per cent.
Mr Allbert told the delegates that on three different Britishbuilt tractive units there had been a wide difference in the amount of wear. The best vehicle showed 43 per cent even wear and the worst 20 per cent. The best showed 55 per cent rapid shoulder wear, the worst 73 per cent. But not all tyre wear was attributed to tractive units.
Mr Allbert pointed out that the design influence is also felt in the semi-trailer market. While the fixed or unsteered axle on a tri-axle trailer gave perfectly acceptable performance in the USA, it was less acceptable in the UK. This was because the American operator travelled most of his distance over motorways while in the UK the tyres were subjected to high cornering severities.
He believes that the expenditure required to adopt a self-steering trailer suspension will be more than justified in improved tyre wear when measured against the total life of a trailer. The same comment could apply to wide spaced ' twin-axle bogies.
On the question of vehicle maintenance, he pointed out that a misaligned chassis had the same effect when travelling straight as it would have if the vehicle was continuously cornering.
On. matters well within the operator's control he stressed that poor pressure maintenance and mismatching twins were costly matters which could be avoided.
A small reduction in tyre drag would not only give better fuel consumption but also result in less tyre wear and could be effected by maintaining tyres at their properpressure. "It can be shown that 25 per cent underinflation represents 2 per cent greater fuel consumption,he said.
Although agreeing it was wrong to generalise, Mr Allbert said that it was broadly true to say that the maximum fatigue life is achieved through good design and accurate, consistent production combined with correct usage and adequate maintenance of casings.
Dealing with fatigue life, he pointed out that the cost of raw materials used in tyres is primarily related to the price of crude oil and that the wearable tread represents only 10-15 per cent of the material cost. "Today," he said, "techniques of retreading and rebuilding are such that the tyre's useful life may be extended well beyond the initial tread mileage."
In conclusion, he contended that manufacturers are doing all that they can to contain tyre costs and suggested that operators not enjoying the full benefits of the nnanufF,cturer's services should look at their own operations with cost reductions in mind.