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).
Study on the causes of wheel shimmy, focusing on tyres, speed, and wheel types.
| Identifier | ExFiles\Box 29\1\ Scan106 | |
| Date | 8th October 1925 guessed | |
| contd :- -9- (a) A new tyre does not promote wheel wobble so violently as an old tyre: The shimmy starts less easily and is maintained for a smaller period. However, on badly worn tyres whose cords are showing, the shimmy loses its violence as if the tyre no longer re-acts. We conclude that the elasticity of the resistance of the walls, play an important part. (b) The critical speed at which shimmy appears seems to be a function of the tyre pressure (see graphs - beyond 33.5 lbs/sq.in. shimmy is not perceptible on the 12-HP. Renault which cannot exceed 60 m.p.h., perhaps it would appear at 63 to 69 m.p.h.) Forces in play increase as the speed increases. At 95 kms. per hr. it is dangerous to continue driving. At 60 kms. per hr. wobbles do not seem to be dangerous. (c) We have tried different types of tyres(smooth, non-skid, steel studded, broad tread and narrow tread) without making any improvement worth mentioning, to wheel wobble. C: TYPE OF WHEEL. Shimmy appears in much the same way whatever kind of wheel - wood, wire, steel rims Michelin etc. Rim of the wheel. Broad rims 2.55" instead of 2" reduce shimmy. Narrow rims 1.65" instead of 2" make it worse. The tyre is, in the latter case, more unstable laterally and the rolling movement is augmented. With a rim of ordinary breadth we have found that variations of the pressure on the ground can reach 220 to 330 lbs. per wheel. When the pressure reaches its maximum, the tangential re-action of the ground on the more heavily loaded wheel also reaches its maximum. contd :- | ||