THE “ ROAD-PUNCH ” OF HEAVY MOTORS.

Putaruru Press, Volume IV, Issue 155, 21 October 1926, Page 7

THE “ ROAD-PUNCH ” OF HEAVY MOTORS.

By “ road-punch ” I mean the dynamic force per square inch exerted on the road by the wheels of a .moving vehicle ; it is that which should be measured (or graded) ; it is that—and not the weight—which should be taxed for each (new) type of heavy motor (writes F. C. Eve in the Motor), so that designers may be induced to plan vehicles which will do least damage to the road. At present they do not care ; so long as the tyres are not made of steel there is no legal inducement for the heavy motor owner to save the roads.

Now what factors are comprised in this conception of “ road-punch ” ? : Clearly a small wheel and a hard, narrow tyre will conspire to increase road-punch, because they reduce the area which hits the road ; they make the hammer head smaller and harder. Yet what multitudes of heavy motors have such wheels, especially in front. “ Road-punch ” will evidently increase with the speed of the motor, hence the speed limit imposed—but seldom enforced—on heavy motors. “ Road-punch ” depends greatly on road surface, for, with round wheels on a perfeetly-level road, it is nonexistent. But the slightest inequality will lift the wheels to a height dependent on the speed and they will crash down again and indent the road. This dent will lift the next wheels which pass over it. and make another dent beyond. And so we get those infernal ripples on the road which we never knew till the railway strike of 1917 filled the frail old roads with heavy motor lorries. So I call them “ lorry-ripples.” They shape and -shatter all vehicles, and compel slow speeds. I believe each heavy motor has its own wave-length in this regard ; it is a kind of' pendulum effect. At its usual speed a bus, for instance, will produce ripples of a length peculiar to itself, depending on its wheel base, height, and the harshness of its springs, etc. Hence licensing authorities might well stipulate that buses on any one route should be of different types. Then a bus which makes a Ift ripple would tend to iron out the waves of one with a 15in or 18in wave-length. Better still, to refuse to license buses with the destructive solid tyres (as in South France). Fast-moving steel tyres exert the “ road-punch ” of a stone-breaking hammer ; I have seen a stone embedded in the road in this way split radially into several fragments. Another factor in “ road-punch ” is the height of the centre of gravity of the motor in comparison with its wheel base. A long, low body pitches very little ; a high body on a short wheel base pitches into every depression in the road with a forceful and destructive road-punch. Now, how can “ road-punch ” be measured? I have a simple and equitable plan for grading each (new) design of heavy motor into perhaps six grades of road-destroying power for taxation purposes. But, apart from that, I believe my conception and name of “road-punch” is of. value, for it focuses our minds on a factor which can be measured and taxed. In my opinion it summarises nearly all the factors in the wheel destruction of our roads.

It is national stupidity to allow heavy motors of bad design, or by a trifling saving in solid tyres, to waste enormous sums of public money in avoidable destruction of our splendid roads. The mere weight of a heavy motor is a poor guide to the destruction it ' will cause ; the former is statics, the latter depends on dynamics of movement. Hence the present Budget proposal to tax heavy motors by mere weight—although better than nothing—misses the main point of road destruction, which is “ road-punch.” Also it discourages design. Some of the latest motor buses are very heavy, but exert very little “ road-punch,” owing to their clever design.