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 table detailing the specifications and weights of car roofs for Saloon and Limousine models.
| Identifier | ExFiles\Box 41\3\ Scan334 | |
| Date | 12th June 1923 guessed | |
| DETAILS OF BODY CAR ROOFS. DETAILS. | (Saloon) 7-Goshawk-ll. | (Limousine) 3-Goshawk-ll. Average height above frame of roof between windscreen and front and rear step iron. | 4 ft. 5 15/16" | 4 ft. 5 3/8" Width at rear of front seats. | 4 ft. 6 1/2" | 4 ft. 3 5/8" Area of roofing. | 4880 sq.in. approx. | 5377 sq.in. approx. Thickness of roof. | 5/16" approx. | 3/8" approx. Weight of roofs (Wt. of 1 cu.in. of material taken as .02" lbs.) | 30 1/2 lbs. approx. | 40 lbs. approx. Details of roof stiffening. Wt. 1 cu.in. oak .027 lbs. " " " " steel .27 lbs. | Steel 55.5 cu.ins. = 14.9 lbs. Oak 1017.75 cu.ins. = 27.48 lbs. | Steel (?- Oak 938 cu.ins. = 25.3 lbs. Details of top framework of body (1 cu.in. taken as .027 lbs.) | 1270 cu.ins. = 34.3 lbs. | 1270 cu.ins. = 32.7 lbs. Total wt. of roof without steel stiffening. | 92.3 lbs. approx. | 98 lbs. approx. Wt. of steel angle iron. | 14.9 lbs. | (?) Wt. of aluminium drip moulding (.18 lbs. per ft.) | 3 lbs. | H----- Total weight of roof. | 110.2 lbs. | 98 lbs. | ||