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).
Geometric investigation into rear wheel arch clearance issues on the new SS cars compared to the Phantom.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan200 | |
| Date | 5th September 1929 | |
| SECRET. ORIGINAL. -BY: ) FROM DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} HS.{Lord Ernest Hives - Chair} ) Copy to GX. HO. " JG. GY/MNG REAR WHEEL ARCH CLEARANCE. We have reported to you in another memo. some troubles we have experienced with the new SS.{S. Smith} cars at the coachbuilders in connection with the rear wheel arch, and our recommended immediate actions. We have investigated the matter geometrically, and illustrate our investigations on N. sch. 2938. herewith. On the uppermost section we shew the WJ. series rear axle first in black pencil rocked up about the centre of the stationary wheel, secondly about the centre of the road spring (in blue), and thirdly rocked up about an axis on the centreline of the car at the level of the top leaf of the road springs under full load: this is point B., and shews the brake drum shield fouling the wheel arch at about the point it does when we apply the rolling test. The lower half shews a section of the Phantom. In pencil we shew the single wheel bump, the axle being rocked about the centre of the other wheel, and in black ink we shew the effect of rocking the axle about a point on the centreline of the car level with the bottom leaf of the spring under full load. We have reason to believe from these conditions that whereas the rolling of the body on the springs with full load equipment on the Phantom gave a test of the rear wheel arch that was satisfactory, when a similar test is applied to the WJ. series chassis the results are very erroneous. When the mass of the body, which is suspended on two elastic springs, is rolled it will oscillate about its centre of suspension: that will be a point on the centreline of the car at the level of the main leaf of the rear spring. This is point B. on WJ. series, point C. on Phantom. Since WJ. series has a spring which is under the axle, and Phantom a spring over the axle, B. is much nearer the road than C., therefore the body translates much more. It will be seen from the indications in a broken line in pencil that if a wheel arch were made on WJ. series to cater for a similar roll about point B. to that which the Phantom wheel arch now almost will permit of about point C., the actual width between the wheel arches would have to be reduced by inches. Because of the 10,000 miles test results, in which no complaints have been made, and also because we know that there is less tendency for the body to roll at WJ. series than the Phantom, we believe that such a roll as indicated by the rolling test, and by swinging about the point B. can never take place on the road, because it would mean that the springs would be deflected sideways a matter of 1.5" each, and to provide such a deflection enormous forces would be called into play, and the spring fixings would be wrenched off the frame. Therefore the (1) | ||