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).
Chassis deflection caused by front braking on a Bentley a Spectre.
| Identifier | ExFiles\Box 84\2\ scan0236 | |
| Date | 18th December 1934 | |
| HS{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}21/KW.18.12.34. Chassis Deflection due to Front Braking. Bentley a SpectreCodename for Phantom III. When the Bentley front axle was fitted to Peregrine cars we endeavoured to find out whether the axle was stiff enough for maximum front braking. To do this we held an axle rigidly by the spring pad and then applied a couple and force to the pivot pin, simulating an emergency stop with the entire weight of the car on the front wheels, the coefficient of friction between the road and tyres being unity. Under these conditions the old weak axle twisted about 4° but took no permanent set. Subsequent running on Bentley cars showed that conditions far worse than this existed on the road, and that apart from judders axles became twisted between the spring pads and the pivots and bent by the horizontal bending movement of the reaction between the tyre and road. We believe these results are due to the inertia stresses caused by suddenly locking a wheel. We have in hand an experiment to determine how quickly a wheel can be made to come to rest from about 600 R.P.M. We therefore arranged a Bentley chassis so that drawbar pulls in excess of the weight of the whole car were resisted by the front brakes only. The pull on the chassis was increased until the axle had a permanent twist of 2°. While subjected to the pull required for this of 6500 lbs. the pivot lean due to spring buckling and axle twist was 2½° forward. Apart from the axle no other part of the chassis suffered from this test. A SpectreCodename for Phantom III chassis with the original suspension layout was next subjected to a similar test. The maximum load applied was 7000 lbs., after which the pivot lean had altered permanently 7/8° forwards. A superficial examination of the chassis showed that – (1) The spring pots had rotated in the frame. (2) The rear strut of the bottom suspension link had buckled. (3) The yoke was twisted. This may go back when No. (2) is released. | ||