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).
Technical discussion comparing Dunlop (English) and American large tires, focusing on performance issues, construction, and sizing.
| Identifier | ExFiles\Box 42\5\ Scan039 | |
| Date | 19th October 1923 guessed | |
| Oy1-E-101923 -2- 2. Large Tires cont'd.{John DeLooze - Company Secretary} our talk with him that the Dunlop Company have something to sell over here, that is, they know more about the big tire business than the American concerns. I think he will be successful in having the Dunlop standards adopted because, from conversation with him,it appears that most makers of tires here have reached the same stage as ourselves, namely, they have found some of the disadvantages and are stalled until someone shows them a way out. The big disadvantage has been plunging, galloping, and throwing at the rear, a general overliveliness, calling for immensely stiff shock absorbers in the sizes above 5". We attributed this to lack of damping friction in the tire due to the thin wall, because it is less marked in the 32x6 and 30x5 sizes we had 10 months ago (which were "bus" tires with thick walls) than in the recent 34x7s. which are regulation balloon type with the thin wall. Macbeth did not deny this but said they were freer from this defect than the American tires because their tire section is roughly rectangular. He attributes the kicking power of the American balloon tires to the desire of the big balloon section to distort egg shaped by centrifugal force. The English tire with its relatively stiffer tread section and flat side walls has very much less of this effect. At the same time I imagine that it is necessary (and permissable) to tighten up the rear shock absorbers considerably more with the large tires. The other disadvantages of the American tires are noise, mud-slinging and dust raising and increased weight. Macbeth claimed to have overcome this with the narrow or rather standard width of tread which they use on the large tire and with their rim construction to save weight. We actually weighed a 34x7 tire and wheel of the type you use on the 20 HP and found a total of 57 lbs. which seems light. 3. Sizes. Macbeth brought a list of their balloon sizes and corresponding standard tire sizes, from which it appears that your English tires are considerably smaller than ours of a corresponding size. For example our 33x5s are actually 35½" dia. and 5½" wide and roll on a 34" circle. His figures showed that the Dunlop 33x5 rolls on a 33¼" circle with 1400 lbs. load. His 34x7 for the Goshawk is not much bigger than our 32x6. His 36x8 is only a trifle larger than our 34x7, rolling on a 34¼" circle which is practically the same as we find on the 34x7 under a limousine. | ||