Self-tracking Dyson
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for BRS by Tony Wilding
• The first semi-trailer to be built by R. A. Dyson and Co. Ltd. with a wide-spread tandem bogie having twin tyres and leaf-spring suspension has recently been supplied to B RS. It will be used for the carriage of long indivisible loads at up to 26 tons gross trailer weight and, to give maximum strength over the extra-long platform, the trailer main members are of the fabricated and braced type.
The wheelbase of the tandem-axle bogie on the trailer is 6ft Bin. and the rearmost axle is a self-tracking design made by Viberti of Italy. The main advantage in incorporating a self-tracking unit is a reduction in the cut-in on corners although the elimination of tyre scrub is an advantageous feature. Manoeuvring an outfit with such a long semi-trailer can be a problem but with the Dyson design. instead of the semi-trailer turning about a point midway between the axles, the forward. axle becomes the effective pivot point so there is a virtual reduction of 3ft 4in. in the wheelbase of the artic. In some European countries a wide-spread type of tandem bogie is considered as two separate axles and allowed additional load as compared with a close-spaced bogie. In Britain, however, there is no increase over the 18 ton limit for a bogie having a wheelbase of over 4ft but if rumoured changes in regulations are made there may well be an increase to allow 10 tons on each axle and this would give further advantages in allowing for unequal distribution of the load on the platform.
Suspension on the Dyson semi-trailer is by slipper-ended springs with axle location by radius rods and the equalization of load between the axles is achieved through brackets connected by long push rods. The rearmost axle tracks automatically and is fitted with dampers to eliminate "flutterof the wheels.
The wide-spread bogie will be offered by Dyson as a standard model, the leaf-spring suspension being an alternative to the air suspension that was featured on a similar design by Dyson at the Show.