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).
Formula for calculating the rolling resistance of wheels to separate it from aerodynamic drag.
| Identifier | ExFiles\Box 158\1\ scan0214 | |
| Date | 22th September 1938 | |
| 1375 To Hs{Lord Ernest Hives - Chair}/LS.(in America). c. By.{R.W. Bailey - Chief Engineer} c. Rm.{William Robotham - Chief Engineer} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork}12/N.22.9.38. Re: Rolling Resistance of Wheels. In connection with our investigation of the aerodynamic drag of motor cars, it is necessary to know the drag due to rolling resistance, in order to separate the "form drag" from the total drag. This latter we derive from Speed and H.P. track data. We have always assumed that the drag may be taken as being constant for all speeds at 30 lbs/ton. This may have been true with high pressure tyres and over the low speed range with which we deal. M.{Mr Moon / Mr Moore} Andreau who says he had a lot to do with forming Eyston's Thunderbolt says that the rolling resistance is given by the formula: R = 1/P^0.64 { 245.6 + V^3.7 / (397 x P^1.44) } Where R = rolling resistance in lbs/ton P = tyre pressure in lbs per sq.in. V = speed in M.P.H. We attach a graph (to Hs{Lord Ernest Hives - Chair}/LS's copy only) shewing R.{Sir Henry Royce} plotted against V.{VIENNA} for various values of P and you will see for yourself what he says happens. In the case of Thunderbolt at 550 Km/hr. the rolling resistance is three times that of the form drag. We cabled you today as follows:- " What is rolling resistance of road wheel how does it vary with load, speed, and tyre pressure"? and would like to have America's views, and if possible, figures. Ev.{Ivan Evernden - coachwork} | ||