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).
List of weights for different tyre and wheel combinations.
| Identifier | ExFiles\Box 159\1\ scan0160 | |
| Date | 1st October 1927 guessed | |
| X3725 WEIGHT OF TYRES. X20 / X4050 31 X 6.00 tyre fitted on 19" wheel. 57 lbs. 5¼" tyre fitted on 21" wheel. 59 lbs. 33 X 6.75" tyre fitted on 21" wheel. 73 lbs. ---------- | ||