Q We have recently been asked to supply an articulated vehicle,
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the spectfication of the trailer being a 40ft-long drop-frame with tandem-axle running gear on 8.25 x 15 I8-ply tyres.
We have made inquiries to several trailer marulacturers regarding this application and a question arises regarding the permissible gross train weight and the speed restriction imposed when using this type of running gear. The most common opinion Li' that at 16 tons gross train weight, the vehicle is restricted to 50 mph and at 27 Ions gtw 40 mph.
Is this correct and what is the exact law regarding this matter?
A It is not possible to establish the permissible gross train weight of the vehicle which you have described from the information given, This depends on the number of axles and the axle spread.
However, permissible axle weights for particular sizes of tyres are determined by reference to the Society of Motor Manufacturers and Traders' Tyre and Wheel Engineering ManuaL Rated to British Standard, the maximum permitted axle weight for the size of tyre you have quoted is, single tyre 5340kg and twin-tyre 10,170kg. The maximum speed for this type of tyre is given at 40 mph.
The axle weight will be plated in accordance with the standards laid down in the SMMT manual but once plated will be maintained for operation at that weight under Section 146 of the Motor Vehicles (Construction and Use) Regulations 1973.
For further information in regard to tyre size and recommended speed limits in relation to their suitability for operation on a particular vehicle, you should consult the tyre manufacturer.