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 document discussing the merits of Marles type versus worm and nut type steering gears.
| Identifier | ExFiles\Box 153\2\ scan0233 | |
| Date | 1st February 1937 | |
| SECRET 1300 E.{Mr Elliott - Chief Engineer} From R.{Sir Henry Royce}/FJH.{Fred J. Hardy - Chief Dev. Engineer} c. to Sg.{Arthur F. Sidgreaves - MD} c. to Ms. c. to Hy.{Tom Haldenby - Plant Engineer} c. to Da.{Bernard Day - Chassis Design} c. to Mx.{John H Maddocks - Chief Proving Officer} RH{R. Hollingworth}/FJHS/R.1.2.37. STEERING GEARS - ALL CARS. We have now had some experience with the Marles type steering on our cars, and can form a tentative opinion as to whether the change from the worm and nut type has been justified. This question has been raised recently in connection with the Bentley III, where we have the choice of retaining the Worm and Nut, as at present on Bentley II, or changing to the Marles type. The Marles gear we are now using on P.III and 25/30 is our first effort at designing this type. Experience has shown that this design can be considerably improved upon, and we think that the Wraith design will be very much better in all respects. The worm and nut gear, as on Bentley is, on the other hand, the result of many years of experience and development, so that for a fair comparison on the score of cost and weight, the basis should be this gear and the Wraith gear. We give below a comparison of the two types of gear under the following headings:- 1. Road performance. 2. Weight. 3. Ease of production. 4. Maintenance of adjustment. 5. Cost. 1. Road Performance. Undoubtedly the great advantage of the Marles gear is the lighter steering effort under parking conditions, due to its high mechanical efficiency. The efficiency of the P.III and 25/30 Marles gears is 80% while that of Bentley worm and nut is 60% under parking conditions. There is a noticeable viscosity effect with the worm and nut gear which gives a feeling of tackiness when the gear is cold. A thin oil, such as Mobiloil Arctic, reduces this to vanishing point, but is out of the question as it makes sticking very much worse. The position is, therefore, that the worm and nut gear will always necessitate a ratio 35% lower than the Marles | ||