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).
Car weight reduction through the use of smaller wheel sizes.
| Identifier | ExFiles\Box 10\5\ 05-page001 | |
| Date | 19th March 1935 | |
| COPY To E.{Mr Elliott - Chief Engineer} from HE/Rm.{William Robotham - Chief Engineer} c. to SG.{Arthur F. Sidgreaves - MD} c. to Wor.{Arthur Wormald - General Works Manager} c. to Ev.{Ivan Evernden - coachwork} c. to Da.{Bernard Day - Chassis Design} c. to Bh. HE/Rm.{William Robotham - Chief Engineer}25/KW.19.3.35. Handwritten: X4709 68 6- CAR WEIGHTS. There is no doubt that one of the points where the Americans obtain a major saving in weight is in their wheel sizes. An extreme case of what can be saved by using smaller wheels and large section tyres is the Vulture. The Vulture fitted with a Phantom engine has been running about with 7" wheels and 18" tyres. These weigh 73.25 lbs. each. With the Wraith engine in it, a tyre recommended by Dunlops which would carry the weight comfortably is 6.50 section on a 16" wheel. This weighs 51 lbs. complete. In other words, by an alteration to wheels alone we can save approximately 1 cwt. These smaller wheels of course mean raising the car on the springs as recently done with the 20/25, but the axle clearance remains reasonable judging by the American figures which we have. From these figures there is no doubt that obtaining ground clearance by increasing wheel size is a somewhat extravagant procedure from the matter of weight, and we think it is desirable that as far as possible the car should be designed to be able to run with smaller wheels. The 7.50 x 17" tyres at present fitted to the SpectreCodename for Phantom III weigh, complete with wheels, 69 lbs. each. The wheel figure becomes more important on the big car where 6 are carried instead of 5. We appreciate the increased steering difficulty which we have encountered, but this has been overcome by the Americans and presumably if we adopt their type of steering the problem should not be insuperable. We are carrying out some experiments on the Bentley with 6 x 16" wheels, which if successful would reduce the chassis weight by 1/4 cwt. HE/Rm.{William Robotham - Chief Engineer} | ||