DESIGN OF MUDGUARDS

Timaru Herald, Volume CXXXVII, Issue 19626, 21 October 1933, Page 14

DESIGN OF MUDGUARDS

METHODS OF PREVENTING SPLASHING. It is a common experience that some cars protect themselves from mud much more efficiently than do others, and to the owner-driver who does not wish to be continuously expending time and money on having his car washed, great efficiency In mud-guard is much to be desired. Consequently states a recent issue of “The Motor," it is of general interest to examine the reasons which account for the fact that some cars keep clean while others soon become “plastered.” Consider, first of all, an orthodox saloon car equipped with the conventional system of wings and running boards. After quite a short run on a wet road streaks of mud will appear across the rear door panels, soon spreading forward and upward over the front doors and windows. Furthermore, the outer surfaces of the rear wings (facing forward) soon become coated with the same obnoxious material. Obviously, this mud must, in the first place, have been thrown off the front wheels, but the way in which it manages to reach the door panels and rear wings is not, perhaps quite clear. Mud Drips from Front Wings. A certain amount can actually be transferred directly from the wheels to the panels when the car is steered, because few front wings are wide enough to cover the wheels when these are turned through a considerable angle for steering purposes. Consequently, particles of mud thrown tangentially from the tyres (as the tread leaves the road in an upward direction) are caught up by the air and become plastered on to the coachwork. Some tyre treads are worse offenders than others in this fault of lifting mud from ths road surface.

Even more important a source of supply is found in the liquid mud thrown up Inside the front wings. If the section of the wing is a simple curve this mud finds its way along the inner surface and drips from the vertical valance, whence it is blown backward on to the bodywork. Conditions are a little better when the wing section embodies a central rib (forming a channel on the under side), but really efficient protection can only be provided by turning over the edge of the valance to form a proper channel which will convey the mud harmlessly down on to the road. Unfortunately, this form of wing is more expensive to manufacture than is a more simple, but less efficient, section.

New Styles of Mudguard. Here it is opportune to mention a style of front wing which has recently become quite popular, in which the valance (or vertical part) is extended and shaped to follow the curve of the tyre. It would seem that this style has become popularised largely on the score of appearance, but, nevertheless in point of affording protection from mud it has the advantage of diverting the air currents beneath it in such a way that the mud drips from a point much closer to the road than in an ordinary wing. Another new design which has a practical basis consists of prolonging the front wings forward and joining them with very big valances to the dumbirons. Many people dislike the appearance of these wings, but in point of mud protection, combined with a reduction of wind resistance, they undoubtedly present advantages. When a car Is travelling fast on a muddy road a great deal of the liquid picked up by the tyres is thrown off as they leave the road, but an appreciable amount appears to be carried round to fly off like the sparks from a Catherine wheel. It is for this reason that it is found to be advantageous to prolong tffe forward parts of the front wings. The so-called “close-up” wing, secured to stays which are bolted to the back plate of each front brake instead of being secured to the frame, has the advantage of turning with the wheel when the car is steered. Unfortunately it is usually made so narrow, to achieve lightness, that it fails to intercept all the mud thrown from the tyre. Furthermore, it cannot be linked up with a running board. Some very smart designs of car have been brought out by discarding the running boards, but most of them are a nuisance, to say the least of it, from a viewpoint of mud splashing. The important point to remember is that most of the liquid leaves the tyre tread at a point quite close to the road, so 'that the rear part of the front wing must be prolonged, by means of a flexible flap, if there is no running board to act as an interceptor. Otherwise mud will be spattered very liberally along the body. Apart from the unsightliness, this fault is destructive of paintwork because a liquid carrying gritty particles, moving at a high speed, has an effective “sandblasting” action. Importance of Streamlining. Be it noted, in passing, that those front-end difficulties would not be so prominent were our cars streamlined more effectively than at present. The front wings create a big disturbance in the air, enabling the mud to be caught up by eddies which converge upon the rear part of the car and deposit particles thereon just as a river deposits silt wherever its free flow' is checked by an obstruction. Now let us transfer our attentions to the rear end of the car and follow out the subsequent history of mud which is thrown from the back wheels. On a really wet road liquid picked up by the treads rises on a curved trajectory and is caught up in the minor w’hirlwind which follows the fiat rear panel of any moving vehicle. Here, in addition to eddying violently, the air is at a relatively low pressure, and the currents soon impinge upon the rear

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panel, carrying the mud with them. Obviously, two methods are available to reduce the extent of this mudsplashing, one being to cut lown the amount of material thrown off the rear wheels, and the other to secure a smoother flow of air and so to diminish the eddying wake. The first of these requirements is being met to an increasing extent on modern cars by prolonging the backward curve of the rear wings and by filling the space between them with a steel apron of generous proportions.

As already noted, more efficient streamlining will eventually have a big effect on this mud-guarding problem, it being obvious that if the air were flowing smoothing over a car of curved contours, free from projections, there would no longer be available the gusts and eddies by means of which any mud available is so quickly distributed over cars of orthodox shape. This applies most forcibly to the rear-wheel problem. Thus, the modem closecoupled sports saloon, with a curved boot to fill in the suction space at the back, does not create anything approaching the flurrying wake of the square-cut saloon.

So far we have considered only the problem of protecting a car from mud thrown from its own wheels. There is, however, the complementary subject of protection from mud thrown from other vehicles. There are few cars which one can follow on a wet day without being liberally bespattered, and this arises largely through inefficient rear mudguarding which permits the mud to be thrown up and caught in the tail stream. It is easy to notice, on the road, the great improvement effected by modern cars with semi-streamlined tails and efficient .wings. Transverse mud-spattering is another source of trouble, to vehicles and pedestrians alike. It arises mainly on uneven roads, the best example being stone setts in bad condition. Wherever there is a depression, shallow pools of mud and water collect, and w'hen a pneumatic tyre drops into the hollow the disagreeable fluid is displaced sideways. The files of the Patent Office can show innumerable inventions designed to prevent this occurrence, ranging from a simple baffle, swung from a bearing on the hub of the wheel, to more elaborate schemes such as a circumferential flap built on to the walls of the tyre. None of these appears to have come to anything, and it must be admitted that most of them would be both unsightly and expensive to make The solution, therefore, appears to be to keep the roads in good condition and to accelerate the process of replacing setts by more modern surfacings.