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).
The factors affecting a car's braking performance, such as friction, weight, and gradients.
| Identifier | ExFiles\Box 39\2\ Scan216 | |
| Date | 12th October 1925 | |
| R.R. 493A (50 H) (D.D. 31. 12-6-25) J.H.D. EXPERIMENTAL REPORT. -11- Expl. No. REF Hs{Lord Ernest Hives - Chair}/Rn{Mr Robinson}/LG12.10.25 the car behaves. The main deciding external factor is the co-efficient of friction between the tyre and the road. From practical experience we find that this can vary about .7 on a dry tar-macadam road to less than .1 on wet wooden setts. The retardation of a car is directly proportional to the co-efficient of friction between the tyre and the road once the wheels have been locked. If a co-efficient of friction of 1 was encountered, the car could pull up at the rate of 32 ft/sec². If .7, at 22.4 ft/sec², if .1, 3.2 ft/sec². Put in other words, in the first case the car would come to rest from 40 m.p.h. in 54 ft. in the last, in ten times the distance or 540 ft. though in both cases the wheels would be locked. Weight of the car. If all the wheels of the car are in locked the distance in which it will stop is entirely in-dependent of the weight of the car. With the R-R front wheel brake system, the type of body makes a slight difference because the front wheels are not locked when indulging in max. braking, this however, may be neglected in any but tests carried out with scientific instruments. In cars with rear wheel brakes only, the proportion of the weight of the car over the rear axle dictates its maximum rate of retardation. Gradients. As has been pointed out under acceleration, upward gradients have a definite value as retardation, and downward gradients as acceleration. When braking down-hill, there, the car will have a max. retardation which will be the contd :- | ||