From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Guide on the causes of fast tyre wear, including inflation, wheel size, brake adjustments, alignment, and driving style.
| Identifier | ExFiles\Box 158\1\ scan0070 | |
| Date | 14th November 1928 guessed | |
| On over-inflated tyres, the car has a tendency to weave on the road, the tyre being too hard to absorb the small inequalities causes a series of small bounces and the car drifts from one direction to another, causing excessive abrasion and naturally, fast wear. Over-inflation is not so injurious to front tyres as to rear ones. The rear tyres take the driving strain and any series of short hops which the tyre takes is bound to throw excessive wear on the rear tyres. Actual tests have proven that a rear tyre over-inflated ten pounds, will wear out in one-half the mileage as it would if properly inflated. Over-loading is much the same as under-inflation. The load is too great for the air pressure in the tyre. It flattens the tyre out, increasing the contact area and the pressure on the road, thus causing more friction and faster wear. 6. SMALLER DIAMETER WHEELS AND LOWER CENTRES OF GRAVITY.—With the adoption of smaller diameter wheels and lower centres of gravity, more rapid acceleration, quicker braking and higher speed on curves, has been made possible. A small diameter balloon makes more revolutions in a mile than a large one. A tyre 9¼in. smaller in circumference than another will actually deliver 22% less mileage under the same conditions. On the other hand, the small diameter balloon gives greater road-ability to the automobile, and where there is a disadvantage in the way of decreased mileage, there is an added advantage in safety and comfort. Likewise, low hung cars with high wheels wear out tyres rapidly because of the extra speed that is possible on curves. The present demand on the automobile is gradually growing toward better performance. Tyres must endure all this, and therefore, the chances for faster wear are daily growing. Of course, the owner must pay for these advantages in the way of decreased tyre mileage in case they are used to any extent. 7. BRAKE ADJUSTMENTS.—It has been found upon analysis of a given number of automobiles, that 90% have the brakes very poorly adjusted, and the balance is not perfect. The ordinary means of adjusting brakes by jacking up the car and running the wheels, then stopping them, is not perfect, as the eye alone is the gauge, and may not catch the exactness of the stopping. Again, driving the car over a garage floor and locking the wheels to see which one slides first, is no good test, for the wheels may be locked instantaneously by quick depression of the foot pedal, when on the road under slighter depression, one wheel may take hold more than another. Four-wheel brakes must be adjusted perfectly, so that no one tyre will stand more than its normal share of braking. Two-wheel brakes must also be properly adjusted, or one tyre will take the most strain, and wear out faster than the other. Improper brake adjustments will throw more wear on one wheel or another as the case may be, and cause that respective tyre to do more work and consequently wear faster. In addition to this, where brakes may bind it may not be noticed in ordinary driving, but the pull on the tyres causes a slipping effect which leaves spots on the tread and uneven wear. Brake adjustments should be equal and made by specialists in that line. 8. ALIGNMENT, MECHANICAL ADJUSTMENTS, Etc.—These conditions have been with us ever since the advent of automobiles, and consequently have been given a lot of study. Besides this, the average operator knows misalignment wear by its very appearance. It is only mentioned to remind you that mechanical derangement of the automobile will cause fast tread wear and is in the same general category as other operating conditions referred to as new and recently developed reasons. Improperly adjusted or bent steering arms may cause the wheels to be out of line when making a turn. Rims improperly mounted on the wheels will throw a side strain on the tyres in the form of a wobble. Excessive camber may give the tyre a tendency to run under the car, especially if under-inflated, and then snap back in certain spots. These operating conditions all produce spotty or uneven wear. In addition to all the above-mentioned conditions, there are other factors of minor importance, but only here and there prevalent. Fortunately all of the conditions outlined are rarely present at the same time or a tyre would give no mileage at all, but some of these conditions are always prevalent to a greater or less extent and sometimes one or more of them are quite severe. Consequently, there are cases where balloon tyres will be worn down prematurely, although if high pressure tyres were used under the present day conditions like balloon tyres, they will show the same variations in wear. Under these circumstances, it is logical to recommend that all members take a firm stand, refusing to adjust tyres failing from these causes, beyond the control of the manufacturer. It is recommended further that tyres showing fast wear be reconditioned by applying new tread rubber. The customer may not realize it but automobile activity has increased, operating conditions have changed very greatly, people are driving much faster than ever before and good roads, organized traffic systems, and long vacation trips have really put more strain on tyres instead of easing the problem. The variation is growing, and from an industry standpoint, it seems necessary to have a clear understanding on this problem and put the responsibility where it clearly belongs, right in the hands of the tyre user. This variation is not the result of a change in tyre construction or altogether a change in automobiles, but driving conditions and the manner in which automobiles are operated are really the cause. A tyre which would give normal service under some conditions will give only a fraction of that wear under other circumstances. One driver uses big tyres properly inflated, starts up easy, drives at a normal rate, probably not over 40 miles per hour, retaining the reserve for an emergency. He stops easily and he picks his roads carefully. There are probably very few drivers that fall in this class, but one of this kind would get long and satisfactory wear from his tyres. On the other hand, let's take a driver who is inclined to be careless. He has small tyres on his car, over-inflated at one time and under-inflated at another. He constantly drives about 50 miles an hour on the open road and uses his four-wheel brakes to the limit when he stops. When he starts, the accelerator goes to the floor and the car jumps away. He remembers the low centre of gravity in his car and takes turns at high rates of speed. He cares little for the kind of roads he goes over which means extra strain and he gets into roads that cause much abrasion, slipping and spinning. There are, of course, both kinds of drivers and the object of this study is to acquaint the reader with the facts concerning fast tread wear so that the fast driver can be taught to expect less mileage than the man who takes care of his equipment. | ||