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 tread bending losses and losses due to the transmission of torque.
| Identifier | ExFiles\Box 158\2\ scan0035 | |
| Date | 5th June 1939 | |
| - 5 - C. Tread Bending Losses. As each element of tread arrives at the leading point A, it is bent from its circumferential direction to one along the road, this requires an additional concentration of vertical force at A on the tyre due to the road which is not fully compensated for by the additional vertical road reaction at B due to the elements trying to straighten again. There is thus a shift of the resultant vertical force in a forward direction. Between A and B the tread elements are bent by the road in a direction such that the wheel rotation is opposed. D.{John DeLooze - Company Secretary} Losses due to Transmission of Torque. (Fig. 4). It is convenient to look upon the tyre as a brush-like collection of radially projecting "springs", which can be bent sideways, (to explain cornering phenomena), and circumferentially (to explain the losses we are now considering). When the tip of an initially radial "spring" arrives at A it begins to carry some of the horizontal road force acting from right to left on the tyre and resisting its rotation. The sum of the moments of all such forces about the wheel centre, plus the rolling friction torque due to its several causes, together equal the torque T tending to keep the wheel rotating, whilst the sum of the horizontal road forces is equal to the tractive effort RT. This latter is shown reversed at the hub, since we consider forces etc. on the wheel throughout. As the horizontal road force comes on the tip of the spring, the latter begins to bend, so that the wheel hub rotates in the direction of its driving torque T relative to its tread. This is due to shear distortion of the rubber of the tread and probably also of the tyre walls, especially at and approaching the central point C. Here the circumferential shear load on the walls is greatest, since at this point the width of road contact is a maximum, and, therefore, so is the circumferential force acting on the tyre walls. Now as the radial tyre section or cross line of "springs" which we have followed from A to C finds itself to the rear of C, i.e. in regions of progressively reduced width, and therefore of diminishing horizontal road forces, the "springs" begin to get radial again, slipping starting at the outer ends of the contact width line for the section considered, because the shear distortion of the rubber tread is entirely released at such points. Slip also tends to occur to some extent over the whole width, [Text from diagram Fig. 4] T Rr RT radial Bent backward A E C B FIG. | ||