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).
Results of various tyre tests, including rolling circumference and analysis of power losses.
| Identifier | ExFiles\Box 158\2\ scan0016 | |
| Date | 17th May 1939 | |
| -2- Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}15/JH.17.5.39. Types of tyre tested. All the tyres so far tested have been 6.50 x 16. Dunlop Fort. extra low pressure - Rolling circum. 84½" at 21 lb.in.sq. (NEW) 86" " 31 " 86¼" " 32 " 86½" " 43 " Dunlop Fort E.L.P. (1/3. tread remaining). - Rolling circum. 84¾" at 22 lb.in.sq. 86½" " 33 " 88" " 44 " Michelin Pilote - Silent tread - Rolling circum. 86¼" at 27 lb.in.sq. (NEW) Avon. (New) - Rolling circum. 88¼" at 35 lb.in.sq. Avon (¼ tread remaining) - Rolling circum. 84½" at 21 lb.in.sq. 86½" " 33 " 87½" " 44 " India Super (New). - Rolling circum. 85" at 22 lb.in.sq. 88" " 34 " 89" " 46 " Dunlop Track racing (New) - Rolling circum. 87½" at 44 lb.in.sq. Analysis of Results obtained. (See curve sheets 1 and 2) (1) Comparison of front and rear wheel tyre losses. The values for front wheel losses are not necessarily strictly true, as they were obtained by declutching the dyno. and representing the hub horse power as tyre loss + dyno. loss, whereas in point of fact a front wheel does no driving but is a driven member. With India and Dunlop tyres the losses are excessive whether or not the tyres are under load, and in each case it appears that the curves actually cross. In the cases of Michelin and Dunlop Racing tyres about 2½% less horse power is absorbed when the tyres are running light. | ||