Braking Points
Page 27
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IF one tries to consider the question of c mmercial vehicle brakes— particularly with the new 40 mph. s eed limit in mind—it is impossible not to become confused becau so many valid considerations have to be borne in mind. The opera or, for instance, who puts 9 or 10 tons on a 5-tonner and then discov rs that the vehicle takes a long while to stop, or that excessive fade occu s down awkward hills, has nobody but himself to blame. It is certainl true that many operators underestimate the effect on brakes of overloa ing.
On the other hand, the man who carries a h gh, 3-ton load on the same 5-tonner might find that he dare not use the ull efficiency of the system designed for his vehicle because of the ad' itional back-to-front-axle weight transference to be overcome, inherent i the high centre of gravity of his load.
Simply because one employs a good mainte aace routine and the other does not bother, two operators carrying Si.'ilar loads on vehicles of identical age and specification will get very 1 'fferent braking results in the same set of circumstances.
These three instances are enough to illustr te some of the considerations that have to be borne in mind by thos who design vehicles and braking systems. They necessarily have to p oduce an optimum specification, or at best two or three options, but th ir deliberations necesgarily extend far beyond that aim.
It could be argued that the operator may be to blame if he feels he gets an inadequate system because he will not pay the extra for better brakes. If maintenance is neglected because it is b•mplicated then the onus might, in part, be referred back to the manufa turers who may have been faced with the problem of whether to offer a highly efficient system requiring frequent attention or one with a low r efficiency that can easily be adjusted and requires less maintenance.
Not all operators favour efficiency in excess of 50 or 60 per cent. In the main this applies to p.s.v. undertakings, partly because rapid retardation can lead to passenger injury and partly because the high braking potential normally results in more frequent liner or pad replacement. It can be argued that high nominal efficiency is less important than consistent performance.
At least one p.s.v. operator artificially increases pedal pressure required to achieve maximum or near-maximum braking effort, thereby discouraging hard braking in all but emergency conditions. This undertaking has also restricted maximum braking to around 65 per cent., despite the much higher potential of the system employed.
A yardstick of perfection is the non-skid braking system which obviates wheel-locking on every type of road surface but which affords full braking power in excess of that provided by locking all the wheels. Of possibly greater importance, the system automatically caters for both static and dynamic variations in load. Although the system is too costly for application to production vehicles it provides a technical standard by which conventional systems can be judged. There would seem to be some need for a low-cost system that gives the benefits of a non-skid brake with regard to 'automatic variation of front and rear wheel braking to accommodate changes of load, distribution of load and centre of gravity.
But where does all this take operators? It is reasonable to assume that manufacturers give, overall, what the market is prepared to pay for. This does not mean, however, that the manufacturer is entirely free from the responsibility to lead operators towards accepting improved designs—.even if they cost a little more.