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).
Comparing the performance of American and English tires under different conditions.
| Identifier | ExFiles\Box 53\2\ Scan093 | |
| Date | 11th February 1924 | |
| -2- Oy11-E-21124 Taking the points of the Experimental report in order:- (1) Lack of side slip This is very marked with the American tires even though they have a tread much wider than the English balloons or the corresponding standard tire. The balloon tire we find retains its tread pattern much longer than the standard, in fact the 30x5s on the Hup. are scarcely worn at 8000 miles. (2) Braking. We find much improved braking though we have no quantitative results, not having had a decelerometer for testing until lately (when we made one on the principle of a spirit level). Probably this is due to the increased contact surface with the road as well as the less tendency to hop. We took "prints" of the contact of the 32x6 tire with the road as against the 33x5 and found 37 sq. inches of the former at 40 lbs. compared with 22 sq.inches of the latter at 60 lbs. We find with the 32x6 tires that in a heavy sedan it is possible to throw the passengers off the seats on a good road by applying the pedal hard and skidding the wheels. With standard tires this is scarcely possible even though the wheels should not hop. Possibly the lack of an improvement with the Dunlop balloons is due to the comparatively narrow tread. It is very probable also that our American standard tires are much worse for hopping than the English. We know from Mr. Macbeth and from our own comparisons that the English tires are considerably softer both in the tread and the sidewall and are now recommending and fitting American Dunlops because they approach the English tires for riding and braking qualities while retaining the strength in the sidewall which is necessary for our conditions. (3) Snow and Ice. The 32x6 tires were tested throughout last winter which was one of the worst on record. The 30x5 have been run two winters. In neither case have chains been found necessary, although of course in the case of exceptionally bad frozen drifts one would have to use them. We should estimate with American balloon tires the need of chains is in practice reduced 80% and for ordinary use on city streets or ploughed highroads they need not be used. The principal reason for using chains in the U.S. in winter time is the danger of skidding or "tripping" on longitudinal obstacles such as frozen ruts or grooved street car lines. | ||