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).
Study on tire noise, comparing different tread designs and the effect of irregular tread spacing on noise characteristics.
| Identifier | ExFiles\Box 158\1\ scan0128 | |
| Date | 22th January 1934 guessed | |
| -5- To show how quiet the perfectly smooth tire is, the noise with the tire on and off the wheel will be compared. The tire will now be run on the wheel again. (Smooth tire, six seconds). Now, off. (Six seconds). It is very evident that a smooth tire or a plain rib tire is definitely quieter than a tire with the usual types of anti-skid design. However, smooth tires are unacceptable because of their decreased resistance to skidding. The average motorist prefers to have maximum skid resistance, rather than complete elimination of noise. The tire industry has quite generally arrived at a solution to this problem by the use of rib tread tires, which combine good anti-skid properties with reasonable quietness. Such a tire is shown in Slide 7, together with a regular block tire of the same size, 6.50-19, 6-ply. These tires show a considerable difference in total noise. The block tread, number 1 on the slide, will first be run at 45 miles per hour, followed by the rib tread tire, number 2 on the slide. No. 1 the block tread. (Eight seconds of the block tread). Number 2, the rib tread (Eight seconds of the rib tread). The variations in design described thus far, have not involved the possibility of modifying the notes or tones of definite pitch by introducing irregular spacing in the tread design. A note of definite pitch results from impacts of constant frequency. If the impacts occur at irregular intervals, the note of definite pitch is replaced by noise made up from impacts at irregular intervals. This principle has been known to physicists for many years, and it has been used to transform sounds of definite pitch to disorganized noise in various fields; for example, in the design of automobile fans as described by A.D. Gardner*. Slide 8 shows two tires of similar design, except that Tire Number 1 has 60 blocks of uniform length in each row while Tire Number 2 has 55 blocks of 11 different lengths in each row. Tire 1 will first be run from 20 to 50 miles per hour, followed by Tire 2 under the same conditions. Tire 1-blocks of uniform length. (Noise for the range from 20 to 45 miles per hour) Tire 2 - Blocks of irregular length. (Noise from irregular block tire over speed range from 20 to 45 miles per hour.) While the second tire produces noise rather than sound with a fundamental pitch, the total volume is about the same in the two tires, and both tires are decidedly noisier than the rib tread tire previously shown. Noise from the same tire varies at different periods in the tire's life. Rib tread tires which show uniform wear give diminishing noise as they wear down. Tires which develop "heel and toe" or other kinds of irregular wear may become much noisier after they are put into service, but eventually the noise will decrease again as they approach smoothness. FLUTTER NOISE: Another type of noise was described in the classification as "flutter" noise. This may be caused by apparently trivial portions of the design. *S.A.E. Transactions 26 401 (1931) | ||