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).
Page from a report discussing the causes of tire noise and the equipment used for testing.
| Identifier | ExFiles\Box 158\1\ scan0126 | |
| Date | 22th January 1934 guessed | |
| -3- the design. These usually give a noise which can be described as a low buzz or flutter. Third, there are noises due to special types of road surfaces. All tires produce noise on brick pavements due to the rapidly recurring impacts of the successive bricks. Another special source of noise is in the raised expansion joints on concrete roads. They produce a noise which sounds like rapid pronunciation of the words "flip-flop" as the car passes over each joint. Gravel roads produce a drumming noise on all tires practically independent of design. Occasionally, stones are picked up on gravel roads and they may be retained in the grooves of the tire tread for some time after the car is back on paved road, producing a definite noise when they come into contact with the road at each revolution. This is likely to worry a motorist who encounters it for the first time since the noise occurs at each revolution of the wheel. Fourth, there are sounds of either definite or indefinite pitch, which originate from movement of the tread while in contact with the road surface. In straight-away driving on hard roads, these are usually negligible, except with large, low-pressure tires. On soft asphalt, they become quite noticeable with many tires. Movement of the tread in contact with the road is also the source of the howling or squealing noise produced on turns at relatively high speed. In this case, the whole tread is trying to resist a lateral skid, and lateral slippage of part or all of the tread design occurs when the centrifugal force exceeds a critical value. The reduction of noise on turns will be discussed as a separate problem later in this paper. DESCRIPTION OF EQUIPMENT: Slide 1 is a picture of one of the steel wheels used in the noise tests and of a tire in the running position. The wheel is 67.23" in diameter, equivalent to 300 revolutions per mile, and it can be driven at any peripheral speed up to 125 miles per hour. The tire is held against the wheel by a definite dead-weight load but it can be lifted off the wheel at any time by a pneumatic piston. A high grade condenser microphone suitably shielded against wind noises, is placed close to the point of contact between the wheel and the tire. The sounds picked up by the microphone are recorded on aluminum records which can be replayed indefinitely and amplified as desired. The room in which the tests are made is quite free from extraneous noise as will be shown by the records. When we were first asked to give a paper on tire noise, we felt that it would be difficult or impossible to describe the results unless the tire sound could actually be reproduced, and used as examples of noise from different types of tires under different conditions. We would have preferred to show moving pictures of the testing simultaneously with the noise, and for this purpose a sound motion picture would have been ideal. However, the cost of preparing such a picture was found to be at least $1.00 per second for the finished product, so it was felt that a less expensive substitute would have to serve. We have endeavored to combine lantern slides with phonographic reproduction of tire noise to show you some of the steps which have been taken in changing tread design, and in studying the source of tire noise. In order to obtain perfect synchronization of the description and of the tire noises, most of the rest of this paper will be given directly from the records with slides to show the changes in design. We will now transfer to the records for the experimental results. | ||