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).
Experimental results and audio transcript detailing tire impact noise tests.
| Identifier | ExFiles\Box 158\1\ scan0127 | |
| Date | 22th January 1934 guessed | |
| -4- EXPERIMENTAL RESULTS: Impact Noise: The first test illustrates the impact type of sound, using a 6.50-18 tire with the special tread shown in Slide 2. The blocks on the tread of this tire have been rounded, and this tends to emphasize the successive impacts. The tire is run in contact with the test wheel under conditions of normal load and inflation, as shown in Slide 3. In a moment you will hear the sound from the tire as we start the wheel, gradually raise the speed to 60 miles per hour; and then reduce speed to 45 miles per hour. The change in pitch with change in speed will be very noticeable in this test. The noise you will hear is the actual noise as picked up by the microphone and recorded on the record. If it seems unusually loud, please remember that the microphone is close to the tire. After the speed has been held at 45 miles per hour for a few seconds the tire will be lifted from the wheel, and the noise for the next five seconds will be the combined room noise, motor noise, and wind noise from the wheel, which could not be easily eliminated. We will now start the wheel. (noise record of first tire, slowly raised from 0-60 mph - then back to 45. Hold at 45 for 5 secs, and then remove tire from the wheel to get room noise) This is a very noisy tire. The only use we can think of for such a tire would be on fire engines where it should considerably reduce the wear and tear on the sirens. The next experiments are with a 5.25-18 U.S. Royal shown on Slide 4. The noise from this tire running at 45 mph will now be heard. (Eight seconds of tire noise from 5.25-18 U.S. Royal). You will note that while it is much quieter than the previous tire, there is still a sound of definite pitch which can be traced back to the block spacing. If a small stick is held against the tire as it rotates and the microphone is moved close to the stick, as shown in Slide 5, a note very similar to that of the tire running against the wheel is obtained. To make a direct comparison, we will first listen to the noise of the tire against the wheel again. (Five seconds of tire noise). Now, the noise at the stick. (Five seconds of noise at the stick) Every irregularity in a tread design contributes to the impact type of sound. These sounds can be reduced by reducing the irregularities. A progressive decrease in noise will be observed in tests on the series shown in Slide 6. There are five tires in this series, the first being the regular U.S. Royal, previously shown. The second is similar, except that the blocks are twice as long. This has half as many impacts per second, and the fundamental note is an octave lower than in the regular Royal. In the third tire, the center rows of blocks have been replaced by continuous ribs. In the fourth, only plain ribs are used, and in the fifth, the tire is smooth. The sounds from these tires at 45 miles per hour will now be heard. First, the regular Royal Number 1. (Eight seconds of noise from the regular Royal). Number 2. (Eight seconds, Tire 2). Number 3. (Eight seconds, center ribs). Number 4. (Eight seconds, all ribs). Number 5. (Eight seconds smooth). | ||