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).
The effect of high and low pressure tyres on wheel wobble.
| Identifier | ExFiles\Box 29\1\ Scan148 | |
| Date | 1st October 1925 | |
| H.R. 493a 150 H) (D.D. 31. 12-6-25) J.H.D. EXPERIMENTAL REPORT. -2- Expl. No. REF Hs{Lord Ernest Hives - Chair}1/L026.10.25. deflected. In other words, the balloon tyre absorbs very little energy when tramping is taking place, and so allows the high speed wobble to attain a large amplitude. We have actually measured the angle through which the front wheels turn when wobbling with :- (a) high pressure tyres (33 X 5 at 35 lbs/sq.in.) (b) low pressure tyres (7.25" tyres at 20 /lbs.sq.in.) In the first case it is usually about 7°, in the second case 13° or 14°. With balloon tyres, therefore, the effect on the steering wheel is very great. (4) Low pressure tyres, owing to their thin and flabby casings, cannot be made to run so truly as high pressure tyres. This gives them an inherent tendency to wobble. With 7.25" tyres at 20 lbs/sq.in. it is quite possible for a car to have a low speed wobble from 10 to 20 m.p.h. and a high speed wobble from 45 to 50 m.p.h. upwards without any appreciable wear having taken place in the steering. Under these conditions the car is, of course, quite undriveable. We believe that if a client insists on having low pressure tyres of a section greater than 6", he will be forced back to high pressure tyres in a very short time. (5) Low pressure tyres are bad for low speed wobbles. This is because low and high speed wobbles have a good deal in common. We believe lateral instability and large area of contact with the ground are both instrumental in promoting low speed wobbles. Hs{Lord Ernest Hives - Chair}/Rp. | ||