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).
Suitability and operation of Michelin jacks with specific tyre sizes.
| Identifier | ExFiles\Box 26\3\ Scan015 | |
| Date | 22th May 1919 | |
| R.R. 235A (500 T) (S.D. 408. 28-4-17.) Bm. 2/156/13. To R.{Sir Henry Royce} from EH. c. to CJ. c. to Bn.{W.O. Bentley / Mr Barrington} c. to Da.{Bernard Day - Chassis Design} c. to C EH2/LG22.5.19. RE JACKS X.391. It has always been understood that the Michelin Jacks (type Fred) will not go under the front axle on one of our cars with a 895 x 135 tyre deflated. This was pointed out when the jack was first tested. It was agreed then that when the Jack was used at the front of the car, that it should be put under the front spring close up against the axle. We have never found or heard of any complaints when jacking up the car under the front springs. Being the front of the car, the back wheels can be locked by the brakes to prevent the car running off the Jack. The Michelin jack we use, fulfils, better than any other type of jack we know of, the requirements laid down by the Sale Dept. That is that the jack must lift the car either back or front with deflated or inflated tyres of 895 x 135 and 935 x 135 dia. It does appear as though the pad on the fron axle is no advantage at all because by the time it is far enough out so that the base of the jack will clear the deflated tyre, it is too low down for the jack to be got underneath. We consider the Michelin Jack is the best type of jack that we know of. EH. | ||