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).
Comparison of tyre specifications for the Phantom III, Phantom II, and Humber 'Snipe' models.
| Identifier | ExFiles\Box 158\1\ scan0113 | |
| Date | 21th June 1937 | |
| W/S. To C. from Rm.{William Robotham - Chief Engineer} Replying to C.10/D.15.6.37 and C.8/C.16.6.37, the Phantom III. tyre is the same size as the one we fit to the Phantom II. On the whole the Phantom III weigh slightly less than the Phantom II. Our tests in France which of course are the most reliable figures we know, indicates the difference in tyre life between the two cars is not great and is, if anything, in favour of the Phantom III. With regard to the Humber tyre, you will notice that they use a 16" wheel. We do not use a 16" wheel because if we did we cannot get large enough brake drums on the car. Obviously if a small wheel is used, it is necessary to put up the size of the tyre in order to keep the ground clearance approximately the same. Because the tyre section is large it does not necessarily mean that it will have a greater life than a smaller section tyre on a bigger wheel. As an example, the radius of our Phantom III. tyre is 15.10, the Humber 'Snipe' 14.45. In other words we have about 6" more circumference of tread than they have. Rm.{William Robotham - Chief Engineer} | ||