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).
Technical analysis of tire noise on turns, comparing different tread designs and their performance under various conditions.
| Identifier | ExFiles\Box 158\1\ scan0130 | |
| Date | 22th January 1934 guessed | |
| -7- run at the same load but at 12 lbs. inflation. First, the noise with normal inflation 40 miles per hour - (7.50-15 rib tread tire, 1180 lbs. load, 24 lbs. inflation pressure, 8 seconds). We will now run the tire at 12 lbs. inflation with the tire axle tilted at an angle of 2 1/2 degrees to the test wheel axle. This will produce a lateral slippage of the tread ribs as they pass through the zone of deflection. You will now hear the plain rib tread under these conditions. (Tire noise under these conditions). NOISE ON TURNS: The last type of noise to be discussed is the howling or squealing noise on turns. This noise problem has become much more serious as inflation pressures have been reduced, because the large section, low-pressure tires have a lower stability against side thrusts. When a car is driven around a curve, centrifugal force tends to produce lateral skidding of the car which is resisted by the tires. When the centrifugal force becomes sufficiently high, lateral slippage of part, or all, of the tread design occurs with the generation of noise. In Slide 13 the deflected profiles of 2 - 7.00-16 tires are shown. The tire at the left has six rather narrow rows or ribs each with sharp corners. The other tire has only four rows or ribs, the corners of each being rounded. The ribs, especially those on the outside, are much wider than in the other tire, with a corresponding increase in resistance to deformation by side thrusts. When a side thrust corresponding to the centrifugal force is applied, the tread at the left, in which the ribs are narrow, shows a bending of the ribs and a scraping of the sharp corners with production of noise. Under the same conditions, the wide ribs of the second tire show much greater resistance to deformation. In addition, the rounded corners permit more distortion before noise results. The development of this design is very recent. It is the result of a series of tests involving more than 15 different modifications in tread design which we have made during the last six months with the cooperation of the Buick Motor Co. A method of comparing tires for this type of noise is shown in Slides 14 and 15. The car is run around a dry, circular, asphalt pavement, 340 feet in diameter, at increasing speed until the howling or squealing noise begins. The speed at this point is taken as the critical speed. Under these conditions, the tire with the six, sharp-cornered ribs develops the howling noise at 27 miles per hour, while the improved tire with the four rounded ribs does not develop the howling noise at speeds up to 35 miles per hour which was the limiting speed we could use, because, at this speed, the car body was tilting so severely that the right side fenders were in contact with the tires. Slide 16 shows a complete view of the improved tire. We believe the principles used in this tire are fundamental to a reduction of noise on turns, and expect to see this design quite widely adopted for low pressure service. SUMMARY: Tire noise varies widely in character and intensity depending on the tread | ||