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Will it be 44 tons for artics?
Page 30
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by Tony Wilding • It now seems clear that SMMT Proposals to the Ministry of Transport on the subject of increases in legal maximum weights include the raising of the attic gross combination weight limit to 44 tons. Operation at this weight would require a 6 x 4 tractive unit but it is understood that a proposal has also been made that the limit be raised from the present 32 tons to 38 tons with a two-axle or single-drive sixwheeled tractive unit.
The figure of 44 tons represents an increase of 2 tons over the highest previously known proposals, and follows design work which has shown that even with a 42-ton limit there would be difficulties in transporting 40ft containers grossing 30 tons; a CM road test of an Atkinson 42-ton outfit published on February 21, 1969 illustrated this. The higher weight can be attained on a five-axle artic without exceeding axle-load limits, which no doubt justifies the proposal. But it would need a wide-spread trailer bogie—for 20 tons—and a tractive unit bogie spread of over 4ft for 18 tons if the front axle was not to carry more than 6 tons which is currently considered to be the optimum figure; to go higher would require the use of tyres larger than the 10.00-20 now common, and axles for a higher weight are not in production for normal-haulage vehicles.
To obtain a 38-ton limit would require either a three-axle tractor—probably a twinsteered design—or three-axle trailer as this weight would not be possible on four axles without new designs of front axles, large tyres or an increase in axle-weight limit. The latter is not a possibility but with the prospect of higher limits for attics it would seem logical for changes to be made in the figures for rigid vehicles.
If the tractive unit of an attic is to be allowed to gross 24 tons on its three axles and a three-axle attic is given the same facility, there seems no reason why a sixwheel rigid should not be allowed the same. And if an attic is going to be allowed 44 tons then surely a tractor /trailer combination should be allowed this weight also, although it would require each part to have three axles.
To make changes for attics alone and apparently on grounds related solely to container transport would create numerous anomalies. One that is long overdue for attention is that which requires a second man in the cab of a tractor /trailer combination, particularly when many such vehicles from abroad are allowed to operate in this country with a driver only.
One wonders how hopeful the industry can be of getting a 44-ton limit. There will undoubtedly be a reaction against such legislation from the national Press, the motoring associations and so on.
It is hard to visualize a weight increase of this sort without accompanying legislation limiting such outfits to particular routes. And to meet the current thinking on power-to-weight ratio, engines giving at least 264 bhp will be needed. And then heavier gearboxes, propeller shafts and rear axles would have to be used. Presumably this extra unladen weight has been allowed for in deciding that a tractor and semitrailer designed to carry a 30-ton container will weigh less than 14 tons. The view seems to be that 7.5 to 8 tons will be needed for the unladen tractive unit; this leaves only about 6 tons for a 40ft platform/skeletal.
But what if 40ft containers gross more than 30 tons or have peculiar distribution of the load inside them? Axle loadings would be critical at 44 tons and if added sophistications in the way of in-built weighing equipment, adjustable bogies, an adjustable fifth-wheel, alternative kingpin and so on are not added, the industry may be forced to go back to the Ministry for higher axled limits. And all so that 40ft containers can be carried. I wonder if the MoT will accept the proposition. I wonder even more if 40ft containers are really a proposition for transport by road.