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).
Analysis of tyre performance losses due to various forces and a proposal for alternative testing methods.
| Identifier | ExFiles\Box 158\2\ scan0036 | |
| Date | 5th June 1939 | |
| - 6 - BY/B.4/G.5.6.39. because the high shear distortion of the walls at C cannot be maintained by the road force provided by the reduced width when the section arrives at points to the rear of C, where the vertical road reaction force is less than that on the portion A C, because of tyre bending losses sending the resultant reaction forward. At the rear of C, also, the slipping of some elements, with consequent reduction of their contribution to the total horizontal road force,(because kinetic friction is less than static friction), has a "catastrophic" or cumulative influence tending to cause slipping of all the other elements. Thus there will be more or less slipping over the whole area between C and B, and the energy lost in such slip will correspond to that expended in driving the hub through a greater angular distance than that corresponding to the distance travelled. This energy is expended in irrecoverable bending of the "springs". Because of the forward distribution of the vertical load, and also because friction in motion is less than that at rest, the horizontal force, i.e. propelling force, will be greater on the front half A C than on the rear portion C B. It does not seem likely that these torque transmission losses will increase with tyre softness to any great extent. E.{Mr Elliott - Chief Engineer} Losses due to Internal Air. Since the total volume of air is, when on a smooth road, constant at all times, there is no work lost in compression and re-expansion of the air. Because the cross sectional area of the tube is reduced at the road contact point, air is driven round the tube in the direction opposite to its rotation, and the friction of the air on the inside of the tube causes a small torque opposing the motion of the wheel. Conclusions and Suggestions. It is clear that, whilst the test drum method is convenient for demonstrating comparative losses on various tyres, it gives results which are much too high, so that the absolute value of the rolling losses must be determined with the wheel running on a flat surface. This may be done by several methods :- (a). Two identical wheels press between them a continuous flexible steel band. By symmetry the band will be flat where it passes between the tyres, (except when torque is being transmitted), and will thus represent a continuous road surfac- | ||