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).
Calculating car speeds based on different axle ratios and tyre sizes.
| Identifier | ExFiles\Box 49\1\ Scan194 | |
| Date | 30th June 1920 | |
| x3545 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} Hsl/LG30.6.20. X.3545. AXLE RATIOS. A.3457. X.4050. 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} | ||