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 performance characteristics including precession torque and camber thrust.
| Identifier | ExFiles\Box 170\3\ img147 | |
| Date | 21th January 1938 | |
| S.H. Grylls Esq., Rolls-Royce Limited. U.S. test is correct because it is the forces square to and in line with the path of the wheel that we want to know. It appears therefore (and is confirmed by some German tests on small model tyres) that traction decreases and braking increases cornering power in the sense shown in attached chart (5). While this is contrary to your experience I would not be worried about that. A lot of other things may happen on the car. Rear axle may hop more when braking, or may change its angle relative to the car. Also see limitation of our test outlined below. Precession Torque. Also driving increases precession torque while braking decreases it. Thus, on tyres as above :- Normal max precession torque is 42 lbs.feet at 4.2/3° when running free, 53 lbs.feet at 6° under 13 HP driving, 32 lbs.feet at 4.1/3° under 10 HP braking. Thus drive acts like a lowering of tyre pressure (decreased c.p. increased p.t.) Braking acts like raising the tyre pressure (increased c.p. decreased p.t.) As with so many things on tyres the effect is probably like attached sketch chart, falling back to zero on either side when actual skid takes place, with these curves depending a great deal on wear-condition of treads etc. We have been getting hold of several startling facts lately. Camber Thrust. We had considered that fitting a front stabilizer would have little effect on the total camber thrust of the pair of wheels. On the contrary it decreases the total thrust considerably as shown in attached two charts of camber thrust against load for flat and curved surfaces and for 6-16.4 and 7½-16.6 tyres. (Charts 1 & 2). The camber thrust is greatly affected by the change from a curved drum to a flat surface. -2- | ||