Axles that follow the Primrose path
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• The first Primrose self-tracking three-axle trailer has been built and has started a demonstration tour of operators in the London area, This first model is the most expensive permutation in the range of self-tracking trailers, consisting of a twin-tyred rigid axle flanked at front and rear by a single-tyred PrimroseCeschi self-tracking axle. This arrangement can be used to show the comparative effects of a rigid three-axle bogie, one with the leading axle self-tracking, one with the trailing axle self-tracking and one with both leading and trailing axles self-tracking.
Either self-tracking axle can be locked in the straight-ahead position manually or by flicking an electro-pneumatic switch in the vehicle cab. The wheels centralize themselves in straight-ahead running as a result of both the in-built castor-action and the inclined telescopic dampers acting on the track-rod arms.
The demonstration trailer has a leaf-spring suspension imposing the same weight on each axle, the twins on the centre (rigid) axle being
fitted simply to stabilize the geometry of action and form a focal point for the turning force. With a 4, 8, 4 weight distribution there would be no reason why 8.25-20 tyres could not be fitted in order to reduce cost and weight and gain a lower platform. In practice it is expected that one of the more popular combinations will be to have just the trailing axle selftracking. Tandem bogies. with either a 6-ton single-tyred or 10-ton twin-tyred self-tracking trailing axle, can also be supplied by Primrose.