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).
Page discussing wall bending losses in tyres on flat roads compared to on test drums.
| Identifier | ExFiles\Box 158\2\ scan0034 | |
| Date | 5th June 1939 | |
| - 4 - B. Wall Bending Losses. (1) On flat road. (see Fig.1). From A to C the tyre "spring" elements are being compressed and in resisting this compression exert a reaction on the road. From C to B the tyre elements are re-expanding and exert pressures on the road which are less than the corresponding forces on the compressing side A C, because of the internal friction in the fabric. Thus the resultant upward reaction Z of the road on the tyre will act on the forward side of the centre C of the contact surface A B, and will obviously exert a retarding torque on the wheel = Z x C F = T_B It is clear that the energy absorbed in strain energy, and therefore that wasted in internal friction will increase with the deflection δ = C D of the tyre. For a given vertical load, C D will increase as the inflation pressure and the tyre radius diminish. Thus large diameter tyres, tightly inflated and made of flexible fabric should be used if bending losses are to be as small as possible. These losses are probably more destructive than the dynamical losses, since the energy is converted into heat in the interior of the tyre, where it is difficult to get rid of. Also the energy loss is a direct result of the rubbing, non elastic deformation and other destructive treatment of fabric. (2) On test drum. (see Fig.2.) A similar action takes place to that on a flat road, but it is obvious from the diagram that, for a given contact chord A B, (corresponding to the load and inflation pressure), the displacements of the tyre elements are increased in the ratio D E / D C compared with their values for a flat road. Therefore the energy wasted will be considerably greater in the case of the test drum than on a flat road, the effect being worst when the drum is of small diameter. | ||