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).
Summary of tests on the tractive resistance of pneumatic tyres.
| Identifier | ExFiles\Box 160\2\ scan0030 | |
| Date | 1st March 1920 | |
| A127 Page 2. 3/20 CONTINUATION OF REPORT No. 192 Tractive Resistance of Pneumatic Tyres Summary of Tests on 895 x 135 (Magnum). Load lbs. | Inflation Pressure. | Speed m.p.h | Remarks | Power consumed H.P. | Tractive Resistance lbs/per ton. 1. Cord | 1050 | 40 | 50 | Tyre cool. | 2.65 | 42.4 2. Cord | 1050 | 40 | 50 | Tyre hot. | 2.30 | 36.8 3. Cord | 1050 | 80 | 50 | First few seconds of run. | 3.15 | 50.4 4. Cord | 1050 | 80 | 50 | Steady state | 1.20 | 19.2 5. Cord | 1050 | 60 | 50 | Steady state | 1.60 | 25.6 6. Cord | 1050 | 40 | 50 | Steady state | 2.30 | 36.8 7. Canvas | 1050 | 80 | 50 | Steady state | 2.15 | 34.4 8. Canvas | 1050 | 60 | 50 | Steady state | 2.50 | 40.0 9. Canvas | 1050 | 40 | 50 | Steady state | 3.05 | 48.8 It is evident from these figures that for a given difference of inflation pressure there is a greater variation in power consumption at low pressure than at high pressures. Thus, by changing from 60 lbs to 80 lbs. there is a difference of 0.4 HP. whereas from 40 lbs to 60 lbs. the difference is 0.7 HP. This is a most important fact in considering these matters, because it is only when the tyre is used under-inflated that the bending of the tyre wall is sufficient to be of much account. There is some evidence that when the tyre is very highly inflated, the power consumption may again begin to increase on account of work done in the tread, but this is a minor consideration from a practical point of view. There is incidently a striking result in the paper quoted (United States Bureau of Standards No. 213) namely, that the magnitude of the tractive effort does not appreciably affect the power consumption. i.e. back and front wheels behave nearly similarly with regard to power consumption. .2. | ||