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).
Investigation into complaints of excessive front tyre wear on the Wraith III model.
| Identifier | ExFiles\Box 158\2\ scan0052 | |
| Date | 11th August 1939 | |
| 1339 Ex from Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} c. Rm.{William Robotham - Chief Engineer} [redacted] Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}6/G.11.8.39. F.J. HARDY. FRONT TYRE WEAR ON WRAITH III. Up to the present there have been three complaints in quite a short time; it does not seem possible to say that any particular type of use is responsible, since one complaint comes from a Scottish owner, one from a local owner, who has just had a Scottish holiday, and the third from a Sheffield owner, who makes trips to London fairly frequently. The first two complaints are for mileages of 6,000 or less, the last has covered some 11,000 miles. The Scottish owner has 3/8" toe-in, and the others 1/4" toe-in. Bennett, the Sheffield owner, has obtained a concession of 33% off a pair of new tyres from Dunlops, and we have reduced his toe-in to 1/8" at the same time. Two possible causes for extra tyre wear as compared with the 25/30 suggest themselves: the first is that the vastly superior handling and controllability of the Wraith tend to encourage faster cornering and generally faster driving, and this will obviously increase wear; the second is unnecessarily large toe-in. Justification for this belief is to be found in L.H. Dawtrey's (of Standard's) discussion of Olley's paper at Coventry last year, when Dawtrey said: "The matter on steering is very interesting. I first became aware of the importance of the thrust angle, resulting from the soling of an elastic tyre, when reading a translation in 1926 of the Broulhiet paper on shimmy and wobble. This action he termed everage i.e. the elastic deflection from the plane of the wheel of the tyre contact with the ground. I have since connected it in my mind with excessive nearside front tyre wear, and from a conception of the effect of road camber on this factor there are good reasons for concluding that no toe-in of front wheels should be allowed, which is being borne out in practice. In certain cases toe-out might be allowed". This was mentioned to Rm.{William Robotham - Chief Engineer} some days ago, and as a result he sent the memo Rm.{William Robotham - Chief Engineer}1/R.4.8.39. When comparing our present toe-in figures with those used on axle cars it should be remembered that with independent front suspension movement of the front wheels up or down from the normal position will increase toe-in. For instance, on Wraith, 1" bump increases toe-in by approximately 0.02", 1" rebound by 0.04". Full bump increases toe-in by .14" and full rebound by 1.18". There is therefore every justification for reducing the toe-in with independent front suspension apart from any other considerations. | ||