Studs — a lost technology

Although the products of the motor industry include much of what is due largely to the innovative skills and development techniques of rally drivers and engineers, they might have included even more were it not for the stifling effects of obstructive bureaucracy. One major safety invention, for instance, which has been received with tolerance in some countries, indifference in others and total rejection in others is the tyre stud, simple in concept but having enormous value as an aid to mobility, traction and direction control on snow or ice.

A studded tyre is not one which has been simply moulded with a few handfuls of metal chips thrown into the rubber. That idea is akin to the suggestion that all you need to put a satellite into orbit is a large quantity of Standard fireworks! Studs have slowly evolved throughout several decades of development which created a unique technology. Alas, its progress has been curtailed by legislative restriction and nowadays it is well on the way to being totally redundant.

Early quests for mobility led to the use of snow chains, but the need for controlled handling, on ice as well as snow, demanded more than mere links of steel crudely wrapped around a tyre tread. They got you moving if you were stuck, but progress afterwards was devoid of directional precision except in a straight line. Then came devices, actually moulded into tread rubber, like coiled clock springs, and others which fitted right through the tyre like nuts and bolts. What evolved from these trial and error tactics, for they were little more, was the modern tyre stud with its retaining flanges and hard metal core, punched into a predrilled and adhesive-treated hole in the tread block.

On packed snow or continuous ice enough of these properly inserted studs improved traction and steering tremendously, so “porcupine” tyres became commonplace, each with more than a thousand wicked looking spikes projecting from its tread. They were more for ice racing than rallying, though they were frequently used on rally stages which were completely covered by snow and ice.

But Mother Nature is rarely as understanding as that. Most stages on the Monte-Carlo Rally are rarely more than partially snow-covered, and even in Sweden and Finland rutting usually brings gravel to the surface, both conditions presenting a tricky stud retention problem. Not only should there be enough of the stud projecting above the tread surface to provide grip, but sufficient should be solidly embedded in the rubber to resist the prising forces created when the studded tyre is driven over abrasive surfaces. Almost like an iceberg, in fact; the tip is stable because most of its bulk is beneath the surface.

A badly inserted stud, or one which projects too far in proportion to its total length, will keel over sideways under the stress of use. Worse, it can be ripped out altogether, and the best stud in the world is quite useless if it flies out of the tyre after a few miles.

Most studs are punched into the tread blocks from the outside, but even as late as the ‘seventies Dunlop went back to insertion from the inside to assist retention, using a gaiter to protect tubes from damage by contact with the metal of the stud base flanges. This was not really a success, and much better was the Pirelli “Grippomatic” system which relied on studs being punched in from the outside so that their base flanges rested between two bead layers, not just in the tread rubber.

Retention is one vital factor; having the most efficient tip shape is another, and it was not long before a simple pointed shape gave way to pyramids, chisels, double-chisel and even various kinds of cross-section. With chisels, the knife-edges could be placed with the chamfer facing front or rear, to provide either good acceleration (on uphill stages) or good braking (on downhill stages) whilst edges laid longitudinally could increase directional stability in a sideways slide. Again the chamfer could be used to advantage by providing more grip on right bends than on left, or vice versa. Some studs were even made with double chisels so that fewer of them would be needed to set up a compromise tyre suited to both left and right bends and both uphill and downhill work.

It was about this time that various local authorities began thinking that studs caused road surface damage when used on dry tarmac. This has never been conclusively proved, and we take the view, as many others do, that most surface wear isn’t really surface wear at all, but the result of subsidence caused by the passage of heavy vehicles on roads whose foundations are affected by changing extremes of temperature. This is particularly noticeable in Scandinavia where shallow depressions appear along the wheel lines of traffic lanes. Onto Moulinet, at the foot of the Col du Turini, where studded competition tyres have been accelerated hard on dry tarmac for years, and you will find none of these depressions. This, we believe, is due to the absence of heavy traffic.

Nevertheless, authorities began to legislate against tyre studs even though there was no concrete evidence that they damaged road surfaces. First there were limits on stud length (which governs the amount of protrusion possible), then on weight, diameter, the shape of the tip and the number permitted per unit length of tread circumference. Some countries even went as far as to ban tyre studs altogether, displaying a highly shortsighted attitude.

National legislation affected competition regulations, of course, and the Monte-Carlo Rally had to follow French law, the Swedish Rally the dictates of the Stockholm parliament, and so on. Ice racing rules are still pretty free, for even governments know that the frozen surface of a lake can hardly be affected by studded tyres!

The legislation was gradual, and there were always teams and drivers who would edge as close to the limit of any new rule without actually breaking it. When, for instance, chisel and pyramid tips were considered too damaging and “flat tops and parallel sides” became mandatory, ingenious designers at the Finnish Kometa company produced a stud core with a cross-section resembling a triangle with slightly concave sides. When the top was honed flat, the result was a three-edged chisel and three points, effective for nearly all requirements. This type of stud vanished when circular cross-sections later became compulsory.

Nowadays stud limits are strict, on size, shape, weight and quantity. Cores have to be uniformly cylindrical and flat-topped, and the number per tyre is usually limited to about ten or twelve per ten centimetres of tread circumference. Length restriction ensures that projection is no more than a millimetre or two.

It’s all very well, you may say, to talk of studs for competition purposes, but are they of any benefit to the day-to-day driver whose progress in generally much more sedate than that of the rally driver? Indeed they are; especially as average skill level is appreciably lower than that of an experienced competition driver. The additional mobility adds to convenience and helps reduce the number of stranded vehicles which cause road blockages, whilst the higher safety factor has been proved time and time again.

Even with tyres lightly studded so that only a little over a millimetre of each tip protrudes, a car has improved traction for both acceleration and braking, and far better lateral control for steering. If, for instance, a tyre has four rows of studs, when it is provoked into a slide in a forward direction it will make four furrows in the ice because the studs of each row are in line with the direction of travel.

But in the case of a sideways slide, the studs of each row are not in line with the direction of travel, so the number of furrows will be increased, even to sixteen or more, with a consequent increase in slide resistance and steering effect.

These features alone provide enough justification for the continued use of studded tyres whenever they may be necessary, arid for further development. It is not cheap to have a set of winter tyres studded. and you may question the economics of keeping a set of such tyres for just a few weeks’ use each year, but once you have experienced the increased mobility and improved handling that such equipment provides you will consider the investment worthwhile. In any case, there can be no valid reason for depriving the motoring public, no matter in what country, of such a benefit. — G.P.