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).
Investigation into fitting larger 7 inch section tyres on the Wraith III Limousine.
| Identifier | ExFiles\Box 159\1\ scan0346 | |
| Date | 12th May 1938 | |
| SECRET To Da.{Bernard Day - Chassis Design} from Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork} c. to Ey, Rn{Mr Robinson}, Rm{William Robotham - Chief Engineer}/Grys, Rm{William Robotham - Chief Engineer}/JD.{J. Draper - Frames} [text has been struck through] 1375. WRAITH 111. WHEELS. Owing to the proposal by Sales to build a large batch of bodies for Wraith lll of the Limousine type, having the rear seat moved back and a large boot at the back, increasing the overhang for 46", it has been suggested by the Experimental Department that it may be necessary to fit the car with 17" rims having 7" section tyres, in place of the 6½" section now instructed. At the same time it is thought that this increase in section cannot be applied to the present 4" rims, and that 5" rims will have to be used. We have investigated the effects of this change, and on PD.173 herewith we show the 7" tyres on a 17" x 5" rim on the front wheels. The rim and wheel is that shown on GW.449, and the front hub is that instructed for cast iron brake drums increasing the track .150 as shown on G.CD.152. The tyre is taken from the Dunlop drawing G.DS.765, and the position of the pivot and cross steering lever has been taken from N.Sch.4822. As far as we are able to tell from the data quoted above, the normal clearance between tyre and the cross steering ball joint in the straight ahead position would be .5" and the worst clearance .375. These clearances would appear to be permissible. At the rear of the car the only difficulty we are likely to experience is the clearance between the wheel arch body brackets and the tyre, and Da{Bernard Day - Chassis Design}/JD.{J. Draper - Frames} is investigating whether it would be permissible to reduce this clearance by about .250", which is the difference between the two tyres. A decision on this matter is urgent, because if we fit these bigger tyres it will be necessary to increase the width of the frontwings to give adequate clearance for the front wheel on lock. The rear wings | ||