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).
How out-of-truth tyres, particularly low-pressure balloon types, cause steering wobbles.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan5 | |
| Date | 12th June 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. Expl. No. REF Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/2/L.G. 10.25. To R.{Sir Henry Royce} from Hs.{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to CJ. BJ. c. to RC.{R. Childs} E.{Mr Elliott - Chief Engineer} c. to DA.{Bernard Day - Chassis Design} EY. c. to EP.{G. Eric Platford - Chief Quality Engineer} MX.{John H Maddocks - Chief Proving Officer} c. to Wor.{Arthur Wormald - General Works Manager} OUT-OF-TRUTH OF TYRES. X401 We have previously pointed out that tyres which run out of truth promote steering wobbles. In our experience the trouble that we have had with balanced tyres (high pressure) has been very small - it is only in the case of low pressure tyres of flabby section that the necessity for obtaining some reason for the start of a wobble led us to investigate the amount these tyres were running out of truth. The only way in which we can definitely detect that a tyre is out of truth in a way likely to affect steering wobbles, is to run the car fitted with the tyre on dynamometer drums which are themselves running truly and measure the movement of the axle spring pad relative to the drums as the wheel is rotated. Spinning the wheel on its hub and observing the out of truth of the periphery of the tyre is not an effective method of checking a tyre, because the whole difficulty is due to variation in stiffness of the tyre carcase, which is only apparent when the tyre is under full load. The particular tyres which were bad in this respect we mention were balloon tyres of 6.75" section, the average high pressure tyre does not vary so much. contd :- | ||