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 from a tyre manufacturer regarding tyre pressure recommendations and load capacities.
| Identifier | ExFiles\Box 29\4\ Scan177 | |
| Date | 27th February 1934 guessed | |
| - 2 - carrying capacity of the tyre as the rim diameter is decreased so that on a 5.50/18 tyre the maximum load that can be carried is 1125 lbs at 36 lbs inflation pressure, and at 30 lbs the permitted load is only 940 lbs. Therefore, based on the British tables at 30 lbs the tyre will be 14% over-loaded but based on the Tire & Rim Association tables it will be 29% over-loaded. The lower values in the American tables have been arrived at due to the different operating conditions in that country, namely, generally higher horse power cars with greater speeds, a condition which we have even to a more marked degree with the Bentley. For the above reasons, we do not feel comfortable in sanctioning the still further lowering of the pressures from 33 to 30 lbs. We are prepared to allow the pressures in the front tyres to stand at 35 in view of your recommendations, but we do not like to recommend in the instruction book pressures as low as 30 lbs in the rear for general use. We would much prefer to make the recommendations:- Front Tyres............ 35 lbs. Rear Tyres............. 33 lbs. and to allow the third paragraph to stand as at present. Yours faithfully, INDIA TYRE & RUBBER COMPANY LIMITED. Works Manager. | ||