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).
The riding qualities of Phantom and 20Hp cars, focusing on tyres and road springs.
| Identifier | WestWitteringFiles\T\2July1928-December1928\ Scan032 | |
| Date | 20th July 1928 | |
| HS.{Lord Ernest Hives - Chair}) FROM R.{Sir Henry Royce} EP.{G. Eric Platford - Chief Quality Engineer}) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} to BJ. BY.{R.W. Bailey - Chief Engineer} PN.{Mr Northey} CWB ORIGINAL. R2/M20.7.28. PHANTOM AND 20Hp. RIDING QUALITIES. X7410 X7820 X5410 X5820 X8410 X235 TYRES. Naturally we must have low pressure tyres for both these cars, so frantic efforts should be made to get hold of the 20" rims and tyres suitable for the 20HP, as well as the 21" X 6 3/4" that is standard on Phantom. No notice should be taken of the maker's requirements of air pressure for these tyres as it will be entirely dependent on the load they have to carry, and with the lightweight Weymann body experience it may be necessary for a 6" tyre to be down to 20 lbs. per sq. in. In your investigations the deflection should be the thing to note rather than the pressure. We ought to run with the maximum tyre deflection that we find economical for the life of the tyre, and perhaps its non-skidding qualities. More than this apparently we cannot do with the tyres. ROAD SPRINGS. We have always favoured flexible road springs, and we cannot get these too flexible unless we are troubled with the car hitting the buffers. In the true Weymann body that I used in London I am sure that the rating of the road springs, especially at the rear, was too high. Whether it came from the springs being too stiff for the lightweight body, or whether it came from some peculiarity in the nip of the leaves of the springs rendering the rating and mechanical friction so high as to put up the apparent stiffness, could be easily investigated. In fact if there is any mystery in this type of springing, it is not only necessary to check the load the springs have to carry in pounds, but I am sure something would be found by checking the rating - (i.e. pounds required, say per inch of deflection, at the running camber.) Whether it comes from the characteristic due to nip, or to mechanical friction, would also be easily shewn on the test rig, a chart being drawn of the loading and unloading of the springs. There are impressions about that Lemoine and other springs than Firth's, give quite different riding for the same pounds of load carrying capacity. I should be glad of a report as to whether this is so, and if so, whether it is due to the lower rating of the springs, or the less internal friction. I have repeatedly pointed out that we must not depart from flexible springing for the sake of high speed riding, but since we have got hydraulic dampers we must (1) | ||