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).
Performance of 6.75 inch Dunlop balloon tyres compared to 6.00 inch tyres, detailing test results and handling characteristics.
| Identifier | ExFiles\Box 29\1\ Scan246 | |
| Date | 9th September 1926 | |
| X457 To BJ. From Hs.{Lord Ernest Hives - Chair} Hs{Lord Ernest Hives - Chair}2/LG9.9.26. 6.75" BALLOON TYRES. X4565/X7430 see x7430 for reports. With reference to the attached reports. Up to that dated 16.8.26, the car was run with the 6.00" Dunlop tyres. These tyres we do not recommend and as a result of our tests, have been definitely condemned. From 16.8.26 onwards the 6.75" Dunlop balloon tyres were used. It will be observed that with these tyres, high speed wobbles ceased to exist. The wandering complained of, was traced to incorrect setting of the rear dampers. Our own opinion is that these tyres on 12-EX are superior to the high pressure tyres for selectiveness, provided they are not run at too low inflation pressures. During the 10,000 miles test they were run at 35 lbs/sq.in. on the front. If run at 40 lbs/sq.in. the margin of safety from high speed wobbles would be increased, while the riding of the front of the car would certainly be no worse than that at present obtained with high pressure tyres. The rear would still benefit to the full from the low pressures which could be used. We believe that with 6.75" Dunlop traction tread, well based balloon tyres at 40 lbs/sq.in., the new type axle and hydraulic dampers, the tendency to high speed wobble will be no greater than with the present standard axle, friction dampers and high pressure tyres. The benefit with regard to riding comfort and rattle elimination is enormous on bad contd :- | ||