15-02-2018, 02:56 PM
Wheel patter, which I know as axle tramp, is not confined to Austin Sevens. Large and heavy cars are very prone to it. A friend always drove Rover 14s and 16s which suffered from this. I had a Daimler Light Straight 8 which was also prone to it and W O Bentley while working for Rolls Royce testing the new 3-1/2 litre Bentleys had an accident caused by it. On these cars it happens at around 70mph while traveling in a straight line. At a certain frequency the front axle starts to oscillate with the front wheels jumping in the air alternately. It's very scary.
The cause is believed to be lack of rigidity in the front section of the chassis. On these cars there's a big section with no cross bracing because the space is taken by engine and gearbox.
It is aggravated if the shock absorbers are weak and Daimler adopted cross-braced chassis where the bracing extends forward alongside the engine. All these cars were fitted with harmonic front bumpers consisting of a flat spring steel bar across the car with lead weights at the ends. They were tuned to the frequency at which this happened. Akin to the dampers fitted to high-tension cables on pylons.
The cause is believed to be lack of rigidity in the front section of the chassis. On these cars there's a big section with no cross bracing because the space is taken by engine and gearbox.
It is aggravated if the shock absorbers are weak and Daimler adopted cross-braced chassis where the bracing extends forward alongside the engine. All these cars were fitted with harmonic front bumpers consisting of a flat spring steel bar across the car with lead weights at the ends. They were tuned to the frequency at which this happened. Akin to the dampers fitted to high-tension cables on pylons.
Jim