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).
Letter from Dunlop Rubber Co. Ltd. discussing the effects of different tyre and rim diameters on tyre life.
| Identifier | ExFiles\Box 157\1\ scan0018 | |
| Date | 1st March 1932 | |
| COPY From: DUNLOP RUBBER CO.LTD. Fort Dunlop Erdington Birmingham ROY{Sir Henry Royce}5/MG HEP/LW.410 Messrs. Rolls-Royce Limited DERBY 1st March.1932 Dear Sirs, We thank you for your letter of the 26th ult. and in connection with the writer's interview with Mr. Royce when the question was raised of comparative performance of various sections of tyres on different rim diameters, we have pleasure in giving you the following information. From tests carried out, we find that the effect of changing from 19" to 18" diameter rims and from 18" to 17" diameter, in all three sections you mention - namely 5.25, 5.50 and 6.00, is to decrease tyre life 6-7%. The drop from 19" to 17" diameter will give a decrease in tyre life of 12-14% approximately in all sections mentioned. The above figures apply in cases where effective gear ratios have been maintained constant by altering axle ratios. When change in tyre diameter is made without any alteration to gear ratios, except that due to the change caused by the effective radius of the tyre, these figures do not apply, owing to altered performance of the car. We carried out tests of the same section of tyre on 18" v 21" rims on two cars of different manufacture, one with a four-speed box and one with a three-speed box, and found that the change had in one case the effect of decreasing the life 30% and in the other case, only 10%, the apparent discrepancy being caused by altering the effective gear ratio. (Continued) | ||