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).
And comparing Dunlop's figures for tyre rolling resistance against the 'Société Continentale' formula.
| Identifier | ExFiles\Box 158\1\ scan0222 | |
| Date | 12th October 1938 | |
| 133A To Da.{Bernard Day - Chassis Design}.. from Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} c. By.{R.W. Bailey - Chief Engineer} Rm.{William Robotham - Chief Engineer} Rm{William Robotham - Chief Engineer}/Swindon. c. Ev.{Ivan Evernden - coachwork} Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}3/N.12.10.38. Tyre Rolling Resistance. Dunlop figures for 7.00-18.00 and 6.50-17.00 Tyres. Figures for the rolling resistance of tyres of the above size were included in a letter to Rm{William Robotham - Chief Engineer}/Gry.{Shadwell Grylls} from the Dunlop Rubber Co. reference HEP/WS.730.D. of 4.10.38. The figures for H.P. absorption of the tyres given in that letter have been converted into rolling resistances in lbs/ton and are given in a table accompanying this memo. One reason for asking for these figures was to discover whether the "Société Continentale" formula, mentioned in Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}16/N.1.10.38, is correct, and accordingly on the accompanying graph the curves of rolling resistance calculated from this formula are drawn and the Dunlop figures are then plotted in to show their relationship to the curve. The Dunlop points plotted are in each case the mean of all the readings for the particular speed and tyre pressure in question, and the small figure by each point gives the number of readings whose average has been taken. For this purpose the fact that two sizes of tyre are included in the readings has been ignored. It will be seen that there is reasonable agreement between the Dunlop experimental figures and the "Société Continentale" formula, though this latter appears to increase more rapidly with increase of speed than the Dunlop figures do. This may be due to the fact that all the Dunlop figures appear to have been taken with the same top ply temperature, a condition that does not seem likely to apply on the road for speeds as far apart as 30 and 70 m.p.h. and judging by our experience on the dynamometer drums increase of temperature does lead to increase in rolling resistance. In any case, the maximum speed for which readings are given by Dunlops is 70 m.p.h. and it is impossible to judge from these what may happen at higher speeds. Cont'd.... | ||