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).
Letter analysing the moment of inertia (M.I.) of various wheel and tire combinations to investigate shimmy.
| Identifier | ExFiles\Box 43\2\ Scan188 | |
| Date | 2nd December 1926 | |
| Oy2-E-12226 -2- December 2, 1926 Your note about the decrease in shimmy with a heavier inner tube made me think that it would be well to find the M.I. of our complete 33 x 6.75 wheel and tire, as we believe they are heavier than yours. The "green book" you sent me gives the M.I. of a 33 x 6.75 Dunlop wheel and tire as 2.73 units (slugs-feet squared). Adding 6 lbs. to the inner tube would make this 2.966 units. We swung a wheel on a free-running ball bearing inner hub of pre-f.w.b. type. The wheel was balanced and had a 33 x 6.75 U.S.Ribbed tire newly attached. The wheel and tire without inner hub weighed 87 lbs. Attaching a weight of 2 kilos, (4.410 lbs.) at 1.5142 feet radius, we get a swinging time of 4.285 secs. This gives - M.I. = 2.79 units K² = 1.033 feet squared. Thus our wheels have a slightly greater M.I. than yours with standard tires, but less than yours with the heavy inner tube. Will try to get some heavier inner tubes like yours. Yours very truly, Maurice Olley MO/E | ||