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 regarding recommended tyre inflation pressures for a Bentley, including axle load calculations.
| Identifier | ExFiles\Box 29\4\ Scan176 | |
| Date | 24th February 1934 | |
| PW/HDE. COPY. India V4662 24th February, 1934. Messrs. Rolls Royce Ltd., DERBY. Dear Sirs, For the attention of Mr. Bailey. With reference to the recommendations in regard to inflation pressures for 5.50/18 tyres fitted to the Bentley, we note that you wish to change to recommended pressures from 33 lbs. all around to 35 lbs. front and 30 lbs. rear. We understand that you have arrived at these figures after extensive tests and satisfied yourselves that these are the most satis-factory pressures at which to operate. We should like to put on record, however, that the weights as given us on the car with body are as follows:- Front Axle 1750. Rear Axle 1950. Using these figures and assuming that there are three passengers and driver weighing 150 lbs each, and that the full weight of the two passengers in the rear is on the back axle and also 3/5 of the weight of the two people in the front seats, the loading per axle works out as below:- Front Axle 1750 + 120 = 1870 lbs. Rear Axle 1950 + 480 = 2430 lbs. Front Tyre 935 lbs. Rear Tyre 1215 lbs. The recommended pressure for the 5.50/18 according to the British table = for 1120 lbs would be 35 lbs. The practice of the Tire & Rim Association of America which is also followed on the Continent is to reduce the allowed carrying/ | ||