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).
Calculations for jack height requirements based on rear axle ground clearance for various wheel and tyre combinations.
| Identifier | ExFiles\Box 26\6\ Scan018 | |
| Date | 17th February 1930 | |
| -2- Hs{Lord Ernest Hives - Chair}/AJL.1/4L.17. 2.30.Contd. Rear Axle. Distance from under rear axle (spring sheath) to the ground with bare wheel fitted - (a) 21" wheel = 6.750". (b) 20" wheel = 6.250". Distance from under rear axle (spring sheath) to the ground with complete wheel and inflated tyre fitted and allowing .500" between the tyre and the ground. (a) 21" wheel fitted with 7.00 x 21" tyre = 12.50". (b) 20" wheel fitted with 7.00 x 20" tyre = 12.0". From these figures we get our jack requirements. * (1) Minimum Height = 5.5". (2) Maximum Hydraulic or Mechanical Lift required (Z-Y + 1.5" allowance for cambered and soft roads) = 7.250". (3) Extension = 2.0". Total extended height (5.5" + 7.250" + 2.0") = 14.750". 20/25 HP. CAR. Fitted with (6.00" x 19") Tyres. On the same reckoning we get the following jack requirements for 20/25 HP. car. Minimum Height = 6.40". Mechanical or Hydraulic Lift. 6.70". Screw extension = 2.00". Total Extended Height = 15.10". If we accept we cannot cater for a man who loses a tyre from the rim, then we can add .500" to our minimum height making it 6.00" for Phantom 11. In this case the one jack becomes suitable for both cars. | ||