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).
Article from 'THE AUTOCAR' by John V. Pugh discussing experiments on steering wheel wobble caused by unbalanced wheels.
| Identifier | ExFiles\Box 28\4\ Scan102 | |
| Date | 3rd January 1914 | |
| 12 THE AUTOCAR, January 3rd, 1914. Steering Wheel Wobble. Some Experiments with Unbalanced Wheels. By John V.{VIENNA} Pugh. ON Brooklands racing drivers appreciate fully the vital importance of having their wheels, when complete with tyres, perfectly balanced. If a wheel be out of balance they go to considerable trouble to put it in balance by adding little lead weights held in position by the security bolts. Figs. 1 and 2. Apart from Brooklands and racing generally, very little attention is however paid to the balance of wheels; the reason is that on the road a wheel out of balance only makes an uncomfortable car and difficult and tiring steering, but on the track at the higher speeds it is frightfully dangerous, and it is almost impossible to keep the car on the track. Neither on cars for the road nor for racing has any attempt been made to eliminate the possible effects of a wheel being out of balance. The nearest approach (although it is directed to a quite different problem) is that practice now very usual of making the centre line of the steering swivel pass through the contact between the tyre and the road, and this is done either by putting the steering swivel on an angle as shown in fig. 1, or the wheel on an angle as in fig. 2, or both of them on an angle as in fig. 3. When a front wheel brake is used, the road pulls in a horizontal direction on the wheel, and, if the Figs. 3 and 4. wheel be arranged as in fig. 4, which is the older practice, there will be a tendency to pull the wheel round and cause the car to deviate seriously from the desired direction. In fact, it would be impossible to steer with the front brakes on unless the rare condition obtained of both brakes being absolutely equally powerful. That is the reason that all cars with front wheel brakes must be designed as in figs. 1, 2, or 3, so that the centre line of the steering knuckle passes through the road and tyre contact. To a lesser degree this condition also applies where no front brakes are used, but none of the arrangements shown in figs. 1, 2, or 3 has any more effect than the designs shown in fig. 4 on that part of the steering wobble which is caused by the horizontal component of the centrifugal force of the unbalanced wheel pulling first in one direction and then in the other, and twisting the wheels round about six times per second when a wheel is travelling at about thirty-five miles an hour. Now these centrifugal forces act through the centre of the central plane of the wheel at the point A, and the distance from A to the axis of the steering swivel round which the plane of the wheel can turn is quite Figs. 5 and 6. a big dimension, varying in the average car from three to four inches, so that these forces resulting from the unbalanced wheel produce a turning moment round the steering swivel measured by the magnitude of the force multiplied by this leverage of three to four inches. The formula for ascertaining the magnitude of the centrifugal force is F=.00034 WRN². There are many causes which put a wheel out of balance, such as variation of spoke, felloe, or rim section, variation of density of material, the employment of a bolt valve without security bolts, or counter-weight arranged to balance it, a tyre cover heavier on one side than on the other, or even a very large patch either to cover or tube. Wishing to experiment on the effect of wheels deliberately out of balance, I had the choice of using small weights and very high speeds, or large weights and relatively low speeds, and as I prefer to do circus work of this kind at certainly not over forty miles an hour, I chose the latter plan and employed counter weights in some cases as heavy as 14 lbs. The car experimented on is a four-cylinder 17 h.p. Maudslay with four-seater body, track 4ft. 4in., wheelbase 10ft., weight 3,000 lbs. (about 27 cwt.) with one up, and with rather more of weight on the back than on the front. At thirty-five miles an hour, or about six revolutions per second, the 14 lbs. weight develops a centrifugal force of 600 lbs. As there is only 700 odd lbs. weight on the front wheel this force is nearly sufficient to lift [Handwritten on left margin]: 7x49 | ||