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).
Tyre pressures, braking performance, and a comparison with other vehicle braking systems.
| Identifier | ExFiles\Box 30\6\ Scan113 | |
| Date | 4th August 1921 | |
| contd. -3- 4. Another reason is the use of the present resilient cord tyres definitely reduce the braking effort on bumpy roads unless we take the advantage of running these cord tyres at much lower pressure. A particular point I want to emphasize is that we should clearly point out that it is not advisable to have extra high pressure in the rear tyres, these actually being the ones in which the pressure should be kept to a minimum. For the lightest of bodies this pressure ought to be about 50 lbs. and certainly not exceed 60 lbs. With heavier loads the pressure may be increased, but in all cases the tyre should run with a definite deflection, and a slight bulge sideways when viewed on a smooth road surface, in fact it is much safer to go by this tyre deflection than by the pressure. The correct inflation of the back wheel is of the utmost importance in enabling the back axle to hold the road and the brakes to act efficiently. The brakes on all the American cars we have tried are very unsatisfactory, and unreliable, owing to the poor mechanism. Our mechanism is excellent, but rather costly. The braking of a London taxi-cab (owing to the extra weight on the back wheel) is far better than our car. Owing to the many corners in England, greater braking effort is needed for the same speed than in such a country as France. X.4214. We full understand the extra brake capacity of the Hispano car, owing to the provision of the four-wheel brakes, but it is doubtful whether their scheme is practicable, and it has one very serious defect, and that is, contd:- | ||