Boost for big rigids in new gvw system
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• Heavier sixand eight-wheeled rigid vehicles and more compact rigids and artics will be permitted under the long-awaited revisions to the Construction and Use Regulations which the Department of the Environment has now revealed. These draft revisions, which are to be circulated to operator and manufacturer associations for comment, are presented in the accompanying lists and tables in this issue.
The Society of Motor Manufacturers and Traders said this week that a report in the technical press (not CM) last Friday purporting to be the current proposals on vehicle gross weights and axle spreads was incomplete and inaccurate and was obviously based on a meeting which had been held some time ago, the content now being outdated.
A spokesman for the Freight Transport Association described the earlier published report as misleading and said that there had been a number of telephone calls from members querying the content. The figures quoted, he said, had been taken from Schedule B, which was now out of date.
None of the new proposals permit the current C and U maximum of 32 tons to be exceeded but within that weight limit they offer greater flexibility. Announcing the changes in the Commons on November 11 at question time, Mr John Peyton, Minister for Transport Industries, said that the proposed schedule of weights should allow more economical vehicle design and transport of goods without adverse effects on the highway system or the environment. The more precise calculations of bridge stresses carried out recently had, he said, made it possible to offer a series of reductions in the minimum axle spacings for given laden weights. Vehicles could be shorter overall and there would be greater design freedom; conversely, if the axle spacing remained the same, some increase in laden weight would be permissible.
Mr Peyton said that substantial agreement had been reached with the manufacturer and operator associations on the revised weights and axle spacings. No date of implementation has been fixed but, assuming that no major revisions are called for, it could reasonably be expected that the new schedule will take effect in February or March next year. The Freight Transport Association, welcoming the proposals, told CM this week that the most important thing now was to get swift agreement and implementation. A recent limited survey of some member companies had shown that indecision on axle spacings was delaying over Lim of vehicle orders from just 12 companies.
The biggest alterations proposed are increases from 22 tons gvw to 24 tons gvw for six-wheeled rigids and from 28 tons gvw to 30 tons gvw for eight-wheelers, and the tables show how this may be achieved with different combinations of outer axle spread and individual axle load. Among the smaller rigids, it is now possible to achieve 16 tons gvw on short wheelbases (previously limited to at least 12 ft for this weight) which will benefit tipper operators.
Whereas outer-axle spacing remains the main criterion for the permitted gross weights of rigids (linked now with individual axle loadings as well) the gross weights for articulated vehicles depend principally on the inner axle spacings — that is, the distance between the centre of the rearmost tractive unit axle and the foremost trailer axle. As with rigids, the individual gross weight of tractive units depends upon outer axle spreads.
Although the new system looks complicated, it has been accepted by the manufacturing industry as the only way in which the best possible advantage can be taken of the DoE bridge strength requirements. And it is really not so complex once the basic system is mastered. For rigid vehicles there are the familiar classifications of two axles, three axles and more than three axles. The two-axle machines are quite simply divided into 14-ton or 16-ton gvw according to wheelbase, while the multi-axled rigids have gross weights depending on outer axle spread and individual axle load. The maximum weight permitted on bogies ("closely spaced axles" as the DoE calls them) is dealt with separately — as shown in table 2 — and there are different gross bogie weights according to whether a vehicle has a type of suspension where the axles are equally loaded or a type which puts more weight on one axle than the other. This is the reason for the rather complicated terminology of paragraphs b (ii) and b (iii).
Treated as complete combinations, attics have their gross weight determined by the inner-axle spacings, referred to earlier, but without the individual axle loading stipulation though of course 10 tons remains the limit for any axle; tractive units themselves, however, are treated like rigids, as the lists show.
The bogies of attics have the same weight limits as rigids, but a separate schedule of weights is provided for tri-axle trailers, and this is graded by individual axle weight and not by bogie weight.
Instead of the former 12 weight /spacing categories for attics the new schedule shows 19, and this is because the combinations are separated according to the number of axles on the tractive unit and on the trailer as well as according to their inner axle spacing. Table 1 makes this clear.
The technical editor writes: Although the proposed changes introduce only two new vehicle weights they will allow considerable flexibility within the present weight limits, and one significant change lies in the substantial decrease in inner and outer axle spreads. Many of the proposed configurations may never be produced in quantity, and manufacturers will tend to select the weight-and-space combinations which they think are the best proposition, but the operator will have a far greater range of chassis choice.
Under the proposals it is possible to have a 16-ton-gvw four-wheeler with a wheelbase of less than 9ft, or a 17-ft-outer-axle-spread 24-ton-gvw six-wheeled rigid, or a 22-ft-outer-axle-spread 30-ton-gvw eightwheeler. With such high-load rigid-vehicle configurations available it is likely that the rigid will regain some of its popularity at the expense of the attic. There are provisions for rigid eight-wheelers at 20, 22 and 24 tons gvw but these are unlikely to offer any real advantage over similar-weight six-wheelers. Even the 26-ton-gvw eight-wheeler will have a hard job to sell against the 24-ton six-wheeler as the weight of the extra axle cuts into the payload advantage.
The 28-ton-gvw eight-wheeler, however, may have virtually the same outer axle spread as the 26-ton-gvw vehicle with only a slight loss in maximum plated axle weight. At the top weight the eight-wheeler could become a really useful haulage vehicle, for at 30 tons gvw a 20-ton payload, for example a 20-ton container, becomes possible. For high-density loads where platform length is less important, the eight-wheeler becomes a very real alternative to the attic in fact a 32-ton-attic recently tested by CM had a payload capacity of only just over 19 tons.
I discussed the sixand eight-wheeler possibilities with a Fodens engineer this