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).
Axle ratios and tyre sizes affecting car speeds for pre-war 40/50 models.
| Identifier | Morton\M22\ img043 | |
| Date | 30th June 1920 | |
| R.R. 199 (250T) (SD676 19-7-17) MP180865 To R.{Sir Henry Royce} from HS.{Lord Ernest Hives - Chair}✓ c. to CJ. c. to BN.{W.O. Bentley / Mr Barrington} c. to E.{Mr Elliott - Chief Engineer} c. to DA.{Bernard Day - Chassis Design} c. to PN.{Mr Northey} c. to H.{Arthur M. Hanbury - Head Complaints} ORIGINAL 5 Hsl/LC30.6.20. AXLE RATIOS, 40/50. The pre-war Cars when fitted with a 16 x 52 axle (3.25 to 1 ratio) and 895 x 135 tyres went at 29.6 M.P.H. with the engine running at 1000 revs. The same cars when fitted with 895 x 150 Dunlop tyres would do 31.4 M.P.H. at 1000 revs. If instead of Dunlop tyres we fitted the American 33 x 5 straight sided tyres the car travels at 32.4 M.P.H. at 1000 revs. If we use the low geared axle 15 x 52 (3.47 ratio) and American 33 x 5 tyres, this gives a car speed of 30 M.P.H. at 1000 revs. which is just slightly higher than the old pre-war car gear ratio. The point we wish to make clear is that the larger tyres which we use at present with 15 x 52 axle, gives us approximately the same gear ratio as the 16 x 52 axle with the 135 dia. tyres. Hs.{Lord Ernest Hives - Chair} [STAMP] RECEIVED JUN 30 | ||