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).
Gear ratios, wheel sizes, and coachwork for the Phantom II model, with comparisons to American standards.
| Identifier | ExFiles\Box 19\3\ Scan088 | |
| Date | 1st November 1929 | |
| -2- the traffic jams, therefore, unless the slow speed pulling of the Phantom II engine could be improved, a slightly greater overall gear reduction appears necessary. Of the two figures, that from 10 to 25 m.p.h. is the more important for obvious reasons. If this time could be reduced to 3½ secs. for example, we should have an enviable reputation for "power". This calls for an acceleration of about 4ft/sec. All we know from actual test is that the larger Packard 8, 4-5 passenger standard saloon, will actually show 10-50 in 15 secs. or 3.9ft/sec. with 2 passengers. With the reduced chassis weight of Phantom II, it appears to us that a strong drive to reduce coachwork weights would achieve the desired performance. 3. Wheels and Tires. American 20" x 7", or preferably 19" x 7" straight side tires and rims would pretty well have to be used. The 21" wheel is obsolete in U.S. and the drop-centre tire has not yet arrived. Because of the necessity of truing up the brake drums on the hubs, the best thing to do seems to be to supply the four Dunlop hubs complete and six hub-shells, and to have these wired up to give the desired wheel size in the States. The 19" x 7" tires, which are now becoming Standard in America, replacing the 20" x 7", would probably give the desired reduction in gear ratio for the required acceleration. The standing heights (for road clearances) under normal loading and inflation are - 19" x 7" - 15.500" 20" x 7" - 16.000" Rolling diameters (for speedometer) are approx.- 19" x 7" - 31.2" 645 turns per mile. 20" x 7" - 32.2" 625 " " Because of the general fitting of "special" tires (on which the chauffeur gets a commission) which are nearly always oversize, it is well to have speedometer readings 2% to 4% high, based on above sizes. 4. Coachwork. The sub-frame in America would naturally take the form best suited to the standard coachwork, and would require modifying, therefore, for best results in stiffness, weight saving and economy as applied to the standardised body-sills. It seems better to assume therefore, that subframe and brackets on frame for attaching same should not be applied on left-hand P.II Chassis. However, it is quite possible that a number of subframes or Contd:-- | ||