Comparison table of specifications for four different types of tyres.
| Identifier | ExFiles\Box 65\2\ scan0311 | |
| Date | 13th May 1930 guessed | |
| Header 1: 7" x 19" U.S. Royal Tyre. Header 2: 33 x 6.75 Silent Tread Dunlop. PI Header 3: 6 x 19" S.T. Fort Reinforced Dunlop. D {John DeLooze - Company Secretary} /25 Header 4: 7 x 20 S.T. Fort Reinforced Dunlop. PII 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" | 108.75" | 101" | 107.5" Effective running circum. at 35 lbs/sq.in. | 98.125" | 104.125" | 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 " | 33.5 lbs. | 33 lbs. | 41 lbs. " " inner tube. | 3 " 8 " | 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. | ||
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).