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).
The effects of different rim sizes and tyre pressures on high-speed wobbles and riding comfort.
| Identifier | WestWitteringFiles\S\June1928-August1928\ Scan117 | |
| Date | 22th August 1926 guessed | |
| contd :- -2- The 19" rims make 8% more revs. at any given road speed than the 21" rims with 6" tyres. Therefore the road speed at which the wheel revs. can coincide with the critical criss-cross axle period is reduced 8%. This apparently has just brought high speed wobbles within the speed range of the 20 HP. Summarising the position - it appears that with the 19" rims we shall be in just the same position on the 20 HP. car as we are at present on the 40/50 HP. i.e., that we cannot drop the front tyre pressures below 35 lbs/sq.in. to improve riding comfort because we cannot risk the customer getting high speed wobbles. The rear tyre inflation pressure can be reduced to 25 lbs/sq.in. with no danger as far as we can see to anyone, though in this condition the car is not so nice to drive at high speeds as it wanders. As you suggest, if a customer wants the maximum comfort at low speed, he will have to be prepared to increase his tyre pressures before driving fast. HS{Lord Ernest Hives - Chair}/Rn.{Mr Robinson} | ||