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).
The merits of tyre contact area, comparing low-pressure and normal tyres.
| Identifier | ExFiles\Box 53\2\ Scan040 | |
| Date | 21th August 1923 guessed | |
| 3. In practice with the Low Pressure Tyre the increase in length of contact is ....% as an average, this being of .......% as compared with the 50% increase in sectional down size. 11. "WIDE CONTACT" SHOULD BE AVOIDED. This fact does not mean that there shall be an increased contact width and any increase in such direction would increase the rolling resistance to traction. 12. "LONG CONTACT" HAS GREAT VALUE. Normal tyres of non-skid type are loaded from say 75 to 120 lbs per sq inch of contact area according to the practice of the designer and according to the relative importance of gripping as compared with wearing. Low Pressure large section tyres with their ..... % increase in contact length provide a greatly increased resistance to lateral skidding, and in practice with wheels locked such tyres have a very marked value as regards holding the car straight. 13. INCREASED CONTACT AREA HAS GREAT VALUE. In theory the increased length of contact in conjunction with a normal width of contact would mean that the tyre was not able to get a firm grip on the road, but in practice the Low Pressure tyre when loaded to about 50 lbs per sq inch of contact area is markedly better as regards "GRIP" than normal non-skid tyres - this apparently being due to the increased length of buttress edge on the tread, this being approximately ..... % The greater length of contact means that with a normal tread width there is always an increased area of tread in contact with the ground at any one time. Time and further experience alone will prove whether this gives a longer tread life or not. "Absorbability" is the principal function of a pneumatic tyre and actual static tests demonstrate that on pot holes the Low Pressure tyre's absorbability is .... times as great as normal tyres inflated to normal pressures - reference to Table No..... Photo No...... As regards normal road obstacles such as stones, the Low Pressure Tyre is ...... times more absorbent - reference to Table No...... shews the varying absorption of 3 different types of tyres inflated to varying pressures. Photo No.... | ||