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).
Specification table for Dunlop wheels and tyres.
| Identifier | ExFiles\Box 45\2\ Scan083 | |
| Date | 1st September 1928 guessed | |
| DUNLOP WHEELS AND TYRES. | Type of tyre and wheel. | Effective running circumference. ins. | Effective running diameter. ins. | Circumference with no load - ins. | Dia. with no load ins. | Weight lbs. | REMARKS | | :--- | :--- | :--- | :--- | :--- | :--- | :--- | | 32 X 6" on 20" rim. | 97.25 | 30.8 | 100.5 | 31.9 | 59.5 | This wheel & tyre has been recently standardised. | | 32 X 6" Z. on 20" rim. | 99.125 | 31.55 | 103 | 32.8 | 65 | Marked as the above plus Z. A heavy duty reinforced tyre. | Tyre marked 'Z' received instead of standardised tyre. | ||