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).
Brake testing, propeller shaft durability, and the effects of tyre slip on bumpy roads.
| Identifier | ExFiles\Box 77\1\ scan0104 | |
| Date | 8th March 1911 | |
| R.R. 235A (cont) (W 314. 8.3.11) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 152S. -2- We attempted to measure the minimum time in which the wheels could be stopped (with the car jacked up) when running at 40 m.p.h., but found it to be quite impossible to do so by hand,- it is probably in the region of 1/8 or 1/4 second. The foot brake was applied as hard as possible but the propellor shaft did not fail,- I think the spring of the chassis and brake anchorage is sufficient to save the propellor shaft from failure when tested in this manner (i.e. without road drag on tyres) because there is no doubt that with absolutely rigid brake fixings and chassis the propellor shaft could be twisted by the inertia of the revolving wheels alone. I think the conclusion to be drawn from the above is that with our present footbrake it is almost out of the question to strengthen the propellor shaft sufficiently to withstand really rough usage with a heavy car and high gear,- if we did so I think another part of the transmission would fail, probably the differential gears, and that consequently we should make the footbrake considerably less powerful by reducing the leverage by at least 30 per cent. Another point which I should like to raise in connection with the slip of the tyres on the road is whether it is safe to assume that the wheels will slip even at the figure mentioned above. Under certain circumstances I do not think they will, for instance if the brake be applied violently while the car is travelling on a bumpy road at high speed and both wheels happen to strike the rise out of a hole in the road at the same time, perhaps after having bounced over the hole, then the direction of movement of the wheels and axle has to be changed very suddenly from a forward and downward direction to one which is | ||