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).
Various tyre types, sizes for 40/50 HP and 20 HP models, and an investigation into high-speed wobble issues.
| Identifier | WestWitteringFiles\O\2January1926-March1926\ Scan165 | |
| Date | 16th March 1926 guessed | |
| contd :- -3- | | 40/50 HP. | 20 HP. | |---|---|---| | Well base tyres. | | | | Semi-balloon size. | 6.75 X 33 | 6" X 33 | | Oversize medium pressure size. | 6" for 21" rim. | 6" for 21" rim. | In each case the tyres which are under observation on R's 40/50 HP. and the 10,000 miles 20 HP. are the oversize medium pressure type. We have, however, been running some 6.75" tyres in wobble tests. Though these are not at present altogether desirable from a steering and high speed wobble point of view they give considerably more comfort than the 6" tyre. In addition they might be fitted to the rear of a car only with 6" in front and yet all the tyres would be interchangeable on the well based rims. HIGH SPEED WOBBLES. We took up the point that Daimlers were fitting full balloon tyres from information which we had received and yet were not experiencing high speed wobbles. Our own experience is that with our 7.3" tyres we cannot eliminate wobbles. We were informed that the 7.3" tyres which we have were some of the earliest experimental low pressure tyres manufactured and have only 4 ply casings. At present all the low pressure tyres in circulation have 6 ply casings. This means that the tyres which have produced such violent wobbles in our tests are obsolete. The big tyres seen on Daimlers have six ply casings which we know from experience can be run at high inflation pressures with reasonable immunity from wobbles. Naturally tyres with fewer plies give greater comfort owing to their greater flexibility. | ||