Artics Come Out Best in New Regulations
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AN ANALYSIS BY THE TECHNICAL EDITOR
IT is certain from the amendments to the Construction and Use regulations that the many known criticisms by operators' and manufacturers' associations of the revised proposals put out at the end of March this year have had little effect on the Ministry of Transport. The only really significant modifications to the proposals are that tractive units weighing over two tons unladen can be used with maximum-width semi-trailers. that the amendments can apply to vehicles built since February 1, 1963, and that on tractor/trailer combinations with one trailer the tractor unit can be up to the maximum length of 36 ft. 1 in. for rigids instead of 30 ft. as now.
The amended maximum dimensions continue to be quoted in metres. which may be useful in the light of possible vehicle legislation in the U.K. and Europe. But the figures are not the same in all cases as those existing in Europe and in any event the weights quoted are in British tons, not metric— which are quite different! The reasoning behind this inconsistency is hard to understand—it can lead only to confusion amongst vehicle users.
What should be borne in mind in looking at the regulations is that, in the case of artics, the terms "four axles" and "more than four axles" do not imply only tandem-axle semi-trailers and six-wheel tractive units respectively. The four-axle could be a six-wheeled tractive unit with a single-axle semitrailer and the "more than four axles" could include a two-axle tractive unit and a three-axle semi-trailer.
With the latter layout, which is common in Europe, it would he possible to use a four-wheel tractive unit for 32 tons gross and keep within the new maximum-length dimension of 42 ft. 7-75 in. It will be remembered that in previous discussions on the proposals it was pointed out that although 32 tons was included under the permissible weights for four-axle outfits, this was impossible to achieve as the axle spread had to be 38 ft.
Only Long Lengths?
At first sight it seems ridiculous that this spread should have been quoted, but obviously the 32-ton-gross for four-axle artics is intended to apply to long-load outfits. In other words, for normal goods 30 tons is the limit, but for longlength steel and the like, 32 tons will be possible on the over-length semi-trailers used for these loads. The reasoning is not completely clear—why should longlength outfits need an extra two tons?
Many people find the idea of linking weights to axle spacing hard to take and in some cases the set dimensions do not allow designers the scope to produce the ideal arrangement. This is particularly so for artics where different dimensions would allow in some cases better weight distribution and so on. But I cannot see n12
any semi-trailer maker quibbling about the changes, for they certainly give the four-axle artic a considerable advantage over the eight-wheeler. I can imagine the celebrations in trailer-makers' boardrooms.
So far as eight-wheelers are concerned there is only a little advantage in the amendments; the maximum gross of 28 tons requires an axle spread of 26 ft. and a vehicle to this design with its turning circle of the order of 100 ft. or so seems impractical. So it looks as though 26-ton eight-wheelers will be the rule, compared with 30-ton four-axle artips. Surely only those operators for whom artic operation is completely out of the question will keep to four-axle rigids? There is not the same situation between three-axle rigids and artics, the loads and feasibility of design being equal.
The introduction of the plating scheme will be welcomed by all reasonable people. manufacturers and operators alike. But why is it not applied to all new vehicles, not only those built to the new weights and dimensions? If it were it would clear away many of the injustices in vehicle operation, such as a 7-tonner and a 10-tonner running at the same gross weight, with the former, being lighter when unladen, able to carry more, yet not being designed for it and therefore not so safe. But really, plating is only half the answer, because what is required is a scheme for type-approval, as exists in other countries. Only in this way can an overall standard for such things as braking and frame strength be applied.
Unless this is done there is no guarantee that there will be, and there are questions left unanswered by the amendments as they stand. For example, what about matching? Who is to bear overall responsibility? No doubt the tractive unit will be plated according to imposed load. But the king pin position on the semi-trailer and axle location will affect the distribution of the load. And, of course, alteration of turntable position will affect weight distribution and therefore braking. And what about conversions and chassis extensions?
On braking, it is assumed that the required standards will come into force for all vehicles built after the date on which the amendments come into force and for any vehicles built after Feb. 1. 1963, which are plated as acceptable for uprating. The foot brake figure of 50 per cent will not be hard to obtain on the majority of vehicles but 25 per cent handbrakes will; few existing heavy vehicles can obtain this.
What is not clear is how different the hand and foot brake systems have to be. It will be sensible for them to be completely different, for there would be little point in having an air-operated or assisted handbrake on an air-braked vehicle, for example, with both piped to the same reservoir. There will be little emergency
value in the handbrake if the reservoir became exhausted. Separate reservoirs for the two systems would get over the problem, and here again the artic will score because existing equipment by way of hand reaction valves for semi-trailer brake operation would fill the bill. And generally, over 25 per cent is obtainable on existing outfits.
One strange thing in the braking section is that no mention is made of how efficiencies are to be arrived at. Are they by actual stopping distance or meters? It is understood that at the recent Road Research tests at Crowthorne the various meters tried gave widely differing results. And considering all the fuss about choosing a suitable meter for possible legislation on smoke emission and noise it is very surprising that an approved brake meter is not quoted. Or, if one can be used, where it should be located, as different positions will give varying results.
Logical Move
There may be surprise in some quarters that only vehicles built since February 1, 1963, will be able to be operated at the amended weights, but it is logical really. And how many operators of other than maximum gross vehicles would welcome plating of all vehicles on the road? And is it a practicable proposition anyway? In the discussions that have taken place on the amendments, • vehicle manufactureis originally wanted them to apply to new vehicles only, but subsequently agreed to the 1963 " backdating ". This opposition was because existing rigids would require considerable modification to make them suitable for greater loads —not only on axle spacings but also on axle loading.
Take, for example. a 16-ton fourwheeler which, with the new 10 ton permissible weight on the rear axle, would need a 6-ton front axle. As far as I know, no vehicle with this capacity axle has been offered on the home market., Power-assisted steering would appear to be a requirement also, and if conversion were envisaged the springs would undoubtedly need changing—even if the axle itself and hubs were strong enough. Tyres would be the most important item for they would have to be at least 11-00-20 radial or 16-ply for a front axle load of 6 tons.
There would be the same front axle requirements for six-wheelers which complied with the axle spread and did not have 4 ft-apart bogies, and with the same provisos eight-wheelers would need 5-ton axles with 1000-20 radials or 16-ply tyres. This is taking existing tyre capacity figures,
The limited backdating of the application of the amendments was apparently met after representations by semi-trailer makers who argued, rightly no doubt, that their products could be modified easily. Most have, in fact, been building designs anticipating the amended regulations for some time