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).
Technical explanation of the mechanical causes of rolling resistance in pneumatic tyres.
| Identifier | ExFiles\Box 158\2\ scan0031 | |
| Date | 5th June 1939 | |
| 1339 BY.{R.W. Bailey - Chief Engineer} c. Rm.{William Robotham - Chief Engineer} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork} c. Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden} Handwritten Note: GRY{Shadwell Grylls} There seems to be a difference of opinion on wheel size Rm{William Robotham - Chief Engineer} ROLLING RESISTANCE OF PNEUMATIC TYRES. Explanations are given below of some of the mechanical causes of tyre rolling losses. A.{Mr Adams} Dynamical Losses. (1) On flat road. Due to the softness of the tyre, contact takes place along a line A B instead of at the point D.{John DeLooze - Company Secretary} The instantaneous centre of rotation of the undeformed portion A E B of the tyre will not be at D but will be near C. Assume it to be at C, as it will be if there is no torque transmitted. Let ω = angular velocity of tyre about C, (or any parallel axis such as O the wheel centre.) Each element of the tyre tread on the forward edge of the tyre will, as it comes to A, (the front end of the road contact line), have its vertically downward velocity, (= ω .AC), suddenly reduced to zero, and its energy will be dissipated in vibrations and then in heat. The downward momentum of the tyre elements approaching A will be cancelled by a force Y near A acting upwards on the tyre due to the road. Similarly, as each element of tyre tread arrives at the rear end B of the road contact line, it will suddenly be given an upward velocity = ω . CB. and corresponding upward momentum. This momentum will be derived from the tyre just above B, and will thus give rise to a force Y acting on the tyre near B. The opposed forces Y form a couple = Y x A B resisting the rotation of the tyre. Since the change of momentum of each element is proportional to ω and the number of elements passing A or B per second is also proportional to ω , it is clear that the dynamic resistance couple varies as ω^2. Fig. 1 | ||