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).
Measurement of ground clearance for a 20 HP car fitted with smaller wheels.
| Identifier | ExFiles\Box 106\4\ scan0073 | |
| Date | 6th May 1927 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Rn.{Mr Robinson} c. to BJ. Wor.{Arthur Wormald - General Works Manager} c. to DA.{Bernard Day - Chassis Design} BY.{R.W. Bailey - Chief Engineer} c. to E.{Mr Elliott - Chief Engineer} OY. X5810 Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}9/LG6.5.27. 20 HP. SMALLER WHEELS. 43725 We have measured the ground clearance of various portions of the 20 HP. car with standard 5¼" well base wheels and tyres with the following results. Column A.{Mr Adams} Car on maximum bump at the rear - front springs normal. Column B. Car on maximum bump at the rear - front springs max. rebound. Figures given in inches ground clearance. PORTION OF CAR. A.{Mr Adams} B. Lowest part swan neck. 2.8" 2.4" Petrol tank plug. 3.4" 3.0" Lowest point rear lamp. 4.8" 4.0" Lowest part of rear spring shackles. 8.3" 7.5" The swan neck varies .2" up or down in relation to the tank drain plug. The 6" tyre deflection under maximum bump load is .450" with 35 lbs/sq.in. tyre pressure. Messrs. Dunlop have given us the effective rolling dia. of the 6" tyre on the 19" rims as 29.5" which means that the rolling radius is rather more than 1" less than with the 21" rims. It is therefore apparent that the tank and exhaust swan neck will require some modification if the contd:- | ||