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).
Selection of suitable wheels and tyres for the 20 HP chassis.
| Identifier | ExFiles\Box 159\1\ scan0153 | |
| Date | 25th April 1927 | |
| Y3725 To Hs.{Lord Ernest Hives - Chair} from R.{Sir Henry Royce} c. to BJ. BY.{R.W. Bailey - Chief Engineer} Da.{Bernard Day - Chassis Design} R2/M25.4.27. WHEELS FOR 20 HP. X5810 X4565 X5460 We should not let what Dunlop's say retard us from our endeavours to select a suitable dia. of wheel, and tyre, for our chassis. My suggestion is in no way in the nature of a final command to use a smaller wheel than our old standard, but I understood that the 21" wellbase rim with the 6" low pressure tyre, gave us a wheel larger than our old standard, whereas I was wishing that the external dia. of the tyre should be slightly smaller than our old standard. Firstly, we do not want the frame of the 20 HP. to be higher off the ground than we can help, and secondly, we do not want the 20 HP. to look as big as the 40/50. So what we are really aiming at is a tyre where the weight, etc. should be proportionate to the weight of the two complete cars, which we look upon as a maximum relatively of 3 tons and 2 tons and since the 20 HP. does not go as fast as the 40/50., there will be this in favour of it, so we want a wheel and tyre of about two-thirds the weight, cost, and load carrying capacity of the 40/50, and the life if possible should be the same in car miles. Regarding the life, judging from the 40/50 just returned from France, which has been 10,000 miles on the rough French roads on the single set of tyres, it would look as if we obtained the same life from the 20 HP. It would not be worth while to handicap the car with larger and heavier wheels than is proportionate to give the same life. I am extremely pleased with the 21" wellbase rims and the 7½" low pressure tyres on the phantom, and it would appear that the 19" wellbase rim with the 6" low pressure tyre would be about proportionate for the 20 HP. considering it is two-thirds of the weight, and from 10% to 20% slower. If you agree that there is hope of this size being suitable, will you kindly get a set as soon as possible. You will notice that the smaller dia. of wheel makes it better for our back axle, and also better for our steering, and I think a better general appearance, and should be lighter, and less first cost. I would suggest therefore only be necessary to consider the running costs and the road clearance. Regarding the tank hitting the road this should be more the fault of the tank than the road wheel. We ought to be able to make our lighter chassis run on a wheel of about 32" dia. The 6" tyres on the 21" rims resulted in a wheel so large that it would not go on the back carrier. I saw the spare wheel being carried in a very unsatisfactory manner on the side carrier. This refers to the car at present running in France. It will be remembered that for a long time the wanted | ||