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).
Technical document detailing the nature and characteristics of wheel hop.
| Identifier | ExFiles\Box 170\3\ img015 | |
| Date | 25th February 1936 guessed | |
| -3- (3) Nature of Wheel Hop. When dealing with the high-frequency variety of wheel fight we are interested in the characteristics of wheel hop. As observed on cams this is definitely a resonance frequency. On all modern cars it is close to 500 cycles/min. When tested on drums at slowly increasing speed it occurs quite suddenly at about 500 cycles/min., reaches its peak at 550 cycles/min. and disappears completely at a slightly higher frequency. It is not quite a fixed frequency, however. It slows down with increased height of hop, i.e., as the tyres spend more of their time in the air. Because of this fact, if on a car with little shock absorber action, the wheels are made to hop violently at 550 and the drums are then slowed down gradually, the hop may be built up to an alarming extent at a lower frequency than it would normally occur. If the speed of the drums is further reduced the wheels will suddenly "snap out of it" and run quietly over the cams. When running close to resonance the tyres hit each cam near the leading edge and the rest of the time are in the air. When the drum speed is a little further from resonance the whole front of the car will "hunt" up and down as the relation between cam and tyre changes. The wheel fight, if it occurs, will be worst when the nose of the car is down, and least when the nose is up, and the tyres are just skipping over the tops of the cams. When testing for wheel fight on the road where regular cam-spacing is absent, and where the up and down wheel movement depends on chance contacts with bumps on the road, the element of chance enters into the testing so greatly (slight variations in car speed, angle of approach etc.) that it is difficult to get consistent results on any particular grade crossing, for example. We find it better to go by the general impression on the road. | ||