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).
Tyre pressure recommendations for different axle loads and passenger numbers.
| Identifier | ExFiles\Box 39\2\ Scan184 | |
| Date | 15th February 1926 | |
| - 2 - Our present practice has been, as indicated in our letter of January 12th, to group all axle loads for over 20 cwt. as using 50 lbs. pressure. Your proposals now push up the pressures in the rear tyres of two-thirds of our chassis from 50 to 55 lbs. which we are inclined to think is a mistake, particularly as in chassis of this description the normal condition is to run with light loads, that is, with only two or three passengers where the car itself is arranged for at least six. 5" tyres. -------- In regard to the 5" tyres, your classification for "Not over 24" "Not over 28" are satisfactory for our frent wheels, but the three further classifications, namely, "Not over 31" "Not over 33" "Not over 35" give us two pressures, namely, 60 and 65 lbs, covering 50% of our chassis, which would demand higher pressures than we are running on at the moment, and here again, as in the case of the 20 HP. chassis fitted with 4½" tyres, these two particular axle weights would, generally speaking, be running not at their full axle loads, but less, and one could not expect a chauffeur to arrange to run with say 55 lbs. when only carrying one passenger normally for a time, and put it up to 60 to 65 when his load went up temporarily under full load conditions, with luggage in addition to passengers, it being understood that the length of time a car is run under these extreme full load conditions is quite a small percentage of the life of the car itself. We are strongly of the opinion that for our cars in view of the above facts, the pressures indicated in our letter of January 12th would be more satisfactory to our customers and would not make any measurable difference in the life of the tyre, since the major portion of the service conditions of the car Con. | ||