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 of bump chassis characteristics and frame rigidity for the B.2, B.3, and Wraith III models.
| Identifier | ExFiles\Box 118\3\ scan0030 | |
| Date | 11th December 1937 | |
| LBS This requires consideration To Rm.{William Robotham - Chief Engineer} from Ev.{Ivan Evernden - coachwork} c. to By.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} Rm{William Robotham - Chief Engineer}/Les.{Ivan A. Leslie} Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork}1/N.11.12.37. Dm{D. Munro} 1023. B.3. Bump Chassis. ------------------- We understand the above chassis is being bumped on 3" cams, and that B.2. and Wraith were similarly tested. The B.3. has 2.750 bump, and Wraith 3.125 whilst B.2. has 1.750, but these figures are not strictly analogous. In the case of B.3. and Wraith III, the figures refer to the bump at the wheel, whilst that of the B.2. refers to the bump at the road spring. Due to tyre deflection of the stationary wheel, and the reaction on the unbumped spring, the pivotting centre of the axle appears to be at the centre of the latter. The equivalent wheel bump of B.2. is then 3.600. What is perhaps of greater significance is the torsional flexibility of the B.2. frame which is equivalent to a largely increased bump clearance. We feel that the foregoing conclusions may indicate why B.3. frame has cracked up early on, when bumped on 3" cams, the bump clearance being less than the cam lift, and the frame rigid. In the case of Wraith III the bump clearance is greater than 3" and the frame not highly rigid, and in the case of B.2. the clearance is much greater than 3" and the frame very weak. Ev.{Ivan Evernden - coachwork} | ||