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).
Comparison of rolling resistance formulas and dynamometer test results for determining horsepower.
| Identifier | ExFiles\Box 161\1\ scan0245 | |
| Date | 1st December 1938 | |
| -2- Although this formula would never be used with such data, it was used to see how the results compared with those obtained by dyno. and first principle methods. D.{John DeLooze - Company Secretary} Rolling Resistance derived from the General Motors formula .0112W + .000097WV and K obtained from first principles. The figure for 'Road Wheel Horse Power at Max Lap Speed' which was obtained on the dyno. is in each case corrected to 30°C. and not 15°C as has previously been the case. This figure is again corrected by adding to it the horse power required to drive the dyno. drums alone at the speed in question. Since the Andreau formula for rolling resistance is dependent on tyre pressure, and no record of tyre pressure was made on the majority of the tests a figure of 35 lb/in² has been assumed. In the case of the Buick, where dyno. tyre pressure was definitely 45 lb/in², H.P. available for windage was taken to be (Correct road wheel H.P.) + (H.P. due to rolling resistance of rear tyres at dyno. tyre press.) - (H.P. due to rolling resistance of whole car at road tyre press). In other cases the H.P. due to the rolling resistance of the front wheels only was deducted from corrected road wheel H.P. Dyno. readings were taken in direct gear in each case. ........... CONCLUSIONS. The Andreau 'deceleration' formula for K gives values identical with those obtained by 'dyno and first principle' methods. When the latter method is used with the General Motors formula for rolling resistance instead of the Andreau formula exactly similar results obtain up to speeds approaching 90 M.P.H. and with the tyre pressures adopted. This would not be the case with lower pressures or at higher speeds since the Andreau formula rises much more rapidly than The General Motors formula under these conditions. | ||