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 tyre pressures and alternatives for a 3 1/2 litre Bentley.
| Identifier | ExFiles\Box 29\4\ Scan200 | |
| Date | 12th July 1934 | |
| JY/IK. 12th July, 1934. Bernard Hopps, Esq., THURLASTON, Nr. Rugby. Dear Sir, With further reference to your letter of June 22nd regarding the India Speed Special Tyres on your 3½ litre Bentley it is, of course, well known that Tyre pressures increase on running due to increase in temperature. For your information, we are enclosing a copy of tests which we have made at various pressures from 20 lbs. to 35 lbs. at a speed of 63 m.p.h. and you will note that the increase in pressure in lbs. is more or less constant particularly in the range from 28 lbs. to 32 lbs. The pressure drops back very quickly when the speed is reduced and these figures probably represent the maximum which would be obtained. The recommended pressures have been arrived at as a result of a long series of tests and we believe them to be the best when considering tyre life and the performance of your car. If you are willing to sacrifice some of this performance and are desirous of obtaining still better riding qualities, we would recommend that you fit the next larger size of tyre, namely, 6.00/18 Super Special. This tyre was designed for just such cases as your own and fits the same wheels as the 5.50/18 and can be run at a pressure of 25 lbs. on the rear and 30 lbs. on the front. These tyres are - Continued - | ||