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 of specifications for a standard silent tread tyre and a Dunlop 'Fort' reinforced tyre.
| Identifier | ExFiles\Box 65\2\ scan0300 | |
| Date | 14th September 1929 | |
| x7820 Hs{Lord Ernest Hives - Chair}/AJL.1/MJ.14.9.29. x4050 x7820 x990 7.00 - 21" DUNLOP SILENT TREAD 'FORT' REINFORCED TYRES. This size of tyre has been produced as an alternative to the 33 x 6.75" silent tread tyre at present standard on 40/50 cars. The advantage claimed for them is longer life due to having a greater thickness of 'non skid' tread. They have the following dimensions - 33 x 6.75"Std. 7.00-21"Silent Silent Tread Tyre. Tread 'Fort' Reinforced Tyre. Diam: of tyre inflated to 35lbs/sq.in. but with no load. 34.62" 35.2" Width of tyre at largest section. 6.750" 6.9375" Effective running diam: at 35lbs/sq.in. on rear of 48 cwt. car. 33.13" 33.83" Revs./mile under above conditions. 608.7" 596.4" Weight of outer cover. 38.5 lbs. 44 lbs. Engine revs./min. at 60 m.p.h. in top gear (11/41 axle ratio.) 2269. 2223. Alteration to speedometer reading due to adoption of 7.00-21" tyres. . 2% slow. Is present side spare wheel carrier O.K. Yes. Yes. Is present rear spare wheel carrier O.K. Yes. No. Wheel requires raising, fouls side members. Steering locks. L.H.-36.5° R.H.-32° L.H.-35.5° R.H.-31° Depth of non skid tread. .28125" .4375" Length of arc of tread. 4.625" 5.125" ROAD TESTS. The 7.00-21" tyre is found to give very poor results. | ||