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).
Tests on brake temperature, cooling efficiency, and the effects of different wheel types.
| Identifier | ExFiles\Box 141\2\ scan0334 | |
| Date | 10th September 1940 | |
| Rm{William Robotham - Chief Engineer}/MHR.{M. H. Rigby}1/LT.10.9.40 - 2 - Under conditions of slow heating, calculations from the cooling curves predicted temperatures of 125° C. and 185° C., while in fact they were 115° and 180° C. respectively; and with rapid heating the temperatures were 175° and 197° C. against theoretical values of 183° and 197° C. It was evident that the temperature differences between front and rear were small at high temperatures, but quite considerable at lower temperatures, the change being due to unequal variations in cooling rate with temperature for front and rear. CHECK ON EFFICIENCY CURVES. Bearing this in mind, tests were now carried out on the CRESTA to find the effects of varying pedal pressures. Since we were interested mainly in low pedal pressures, the ratio of front/rear temperatures was sought using 10 and 20 lbs. on the pedal respectively, always at 30 m.p.h. for constant cooling. It was found that, under similar conditions, the figures for front and rear temperatures were approximately the same at the two pedal pressures. EFFECT OF TYPE OF WHEEL. In order to find the difference of cooling due to changing from wire wheels to the pressed steel type, tests were carried out on the Coupé. Apart from the very much better cooling resulting from the change of wheels, this design having a very much larger gap between the rear wheels and their drums, gives an improvement on the rear even greater than on the front. Thus the difference in cooling of front and rear is smaller on the Coupé than on the CRESTA or COMET. A hard drive to Red Gate would not give temperatures above 200° C., a good figure, but even better cooling would be required to keep to this temperature with a B.80 engine. Front and rear temperatures were always very close under these conditions, and only below 100° C. was there a very large difference between them. By fitting discs on both sides of the wheels the cooling was considerably retarded, almost to the same rate as on the CRESTA and COMET on the fronts, but not quite so much on the rears due to the air gap between drums and wheels, still present on the Coupé. SUMMARY OF RESULTS. Taking cooling characteristics of the Coupe with wire wheels as a standard, and calling the cooling rates 85% efficient for front and rear drums on this car:- | ||