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).
Various tyre and rim options for the 20 HP car, requesting rolling circumference data for comparison.
| Identifier | ExFiles\Box 45\2\ Scan069 | |
| Date | 22th May 1928 | |
| S/W. HS.{Lord Ernest Hives - Chair} X4050 CWB8/GM22.5.28. 20 HP. AXLE RATIOS. X5350 Thank you for Hs{Lord Ernest Hives - Chair}1/LG19.5.28. To enable us to make the fullest possible comparison, would you kindly give us the effective rolling circumference of the 4¾" high pressure tyre, which was our former standard on the 20 HP. car. In considering this question from all its points a reference was made to the trade price list of Messrs. Dunlop dated 1st. Dec.1927. and it was noticed that in addition to the 6" tyre on 21" rim, which is now being considered, and the 6" tyre on 19" rim, which is proposed for the distant future, there is also a 6" tyre on a 20" rims. Is there any reason why this tyre and rim should not be standardised pending the alterations to the chassis which will enable the 6" tyre on 19" rim to be used from the point of view of ground clearances? From general considerations, it would appear that the effective rolling circumference of such a tyre should be almost exactly the same as the 5.25 medium pressure tyre at present fitted and that there should be no very great difference in the ground clearances of the car when fitted with either of these two tyres. Would you please therefore let us have this information as soon as possible as it is desired to do something which will enable us to fit the same pattern tread to the 20 HP. as is now proposed for the 40/50 HP. This will not be possible until a decision is made regarding the type of tyre which we shall probably use for the next year or 18 months. CWB. | ||