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 table of specifications for four different tyre models.
| Identifier | ExFiles\Box 42\5\ Scan056 | |
| Date | 20th February 1925 | |
| || 7"x 19" U.S. Royal Tyre. | 33 x 6.75 Silent Tread Dunlop. PI | 6 x 19" S.T. Fort Reinforced Dunlop. AHS. 20/2/25 | 7 x 20 S.T. Fort Reinforced Dunlop. PI |---|---|---|---|---| | Max. width of tyre section. | 6.9" | 6.95" | 6.025" | 6.93" | | " " " tread. | 4.6" | 4.7" | 4.5" | -- | | " " depth " | .325" | .30" | .40" | -- | | Unloaded circum. at 35 lbs/sq.in. | 104.625" | 103.75" | 101" | 107.5" | | Effective running circum. at 35 lbs/sq.in. | 99.125" | 104.115" | 96" | 102.5" | | Wheels revs/mile at 35 lbs/sq.in. | 646 | 608.7" | 660" | 620.5" | | Weight of wheel complete. | 39 lbs. 2ozs | 38 lbs. | 27 lbs 12ozs. | 37 lbs. | | " " outer cover. | 33 " 11 " | 38.5 lbs. | 33 lbs. | 41 lbs. | | " " inner tube. | 3 " 3 " | 4 lbs. 14ozs | 4 lbs. | 4 lbs. 14oz | | " " rubber band | 1 " | 9½ " | -- | -- | | Weight of wheel and tyre complete at 35 lbs/sq.in. | 78 " 12 " | 81 lbs. | 64 lbs. 12 oz. | 83 lbs. | Hs{Lord Ernest Hives - Chair}/AJL. | ||