38 tonnes: what it means
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THE 38-TONNE Regulations were published last week and clarify in detail the Government's proposals. Most of the new information concerns sideguards, a fresh science for the industry, but engineering editor GRAHAM MONTGOMERIE and our technical staff have been through it all with a fine toothcomb and spell out here how you will be affected.
FROM May 1, 1983, 38-tonne gross combination weight outfits with five axles can operate legally in the UK. This is the main brunt of the Motor Vehicles (Construction and Use) (Amendment) (No 7) Regulations 1982.
The C and U axle spacing requirements have been extended to include artics up to 38 tonnes gross, with the definition of axle spacing now being expressed as in the original draft Regulations. Although referred to as "relevant axle spacing" it is now defined as rear axle of tractive unit to rear axle of trailer in contrast to the earlier inner axle spread dimension.
The drive axle weight limit has been upped from 10.17 to 10.5 tonnes to give a little tolerance on weight distribution.
The tri-axle spacings on trailers also go down to 0.7m (2ft 4in) — which limits the individual axle weight to six tonnes — and includes one interesting combination which will permit 7.1 tonnes at a spacing of 1.2m (3ft 1 1 in).
Overall this would limit the five-axle combination to 37.8 tonnes assuming a 16.5 tonne two-axle tractive unit, a small penalty in gross weight which some operators might prefer when balanced against reduced tyre scrub. The disadvantage of this combination is that loading tolerances (small at 2.7m spread) is non-existent at 2.4m. In other words, the wider spread tri-axle bogie not only gives 38 tonnes gcw, but also reduces the risk of axle overloads.
Tyre selection It is likely that big single tyres will be the optimum for a tri-axle bogie. This will improve the roll stiffness as the springs can be moved further out.
York predicts that most people will go for the extra axle on the trailer rather than on the tractive unit as this is the smallest capital investment. At current list prices, a new tri-axle is about £1,400 dearer than a tandem whereas a conversion to an existing trailer is around £2,000 assuming the twin wheel configuration is retained.
One point to stress is that some form of compensation between the axle suspension is obligatory. It is illegal merely to add on a separately sprung axle.
Length changes Also from May 1, 1983, the maximum length of an articulated vehicle is raised from 15m to 15.5m (49ft 3in to 50ft 10in). In the official wording of the Department of Transport, this increase is solely to accommodate "the increased safety and noise reduction features of modern tractor units".
To ensure that the extra length is not merely added to the semitrailer, a new length limit of 12.2m (40ft) is imposed for all semi-trailers manufactured on or after May 1, 1983.
Trailer length has now been officially defined and refers in effect to the platform length thus excluding the thickness of the front and rear walls of a van or a headboard. This definition also clarifies the situation with respect to refrigeration units.
Height limit The height of the new 32.5 tonne-plus category will be restricted to 4.2m (13ft 9in) which the DTp claims will still permit 2.6m (8ft 6in) high containers to be carried. The wording of this particular Regulation is critical.
This height limit applies if the gross weight of the outfit exceeds 32.5 tonnes with no mention of the plated weight so presumably if the vehicle is running empty then the 4.2m limit does not apply. Because of spring deflection in the unladen condition this had been one area which was expected to cause problems.
The Regulation refers to "any tart of the structure of the rehicle" not exceeding 4.2m at 12.5 tonne-plus and defines 'structure" as including "any Jetachable structure attached to he vehicle for the purpose of :ontaining any load". It does not nclude any load which is not a Jetachable structure nor does it nclude any sheeting or other Flexible means of securing the oad. In effect, the new height Regulation applies to laden containers and trailer vans grossing more than 32.5 tonnes.
Sideguards As part of the overall package, sideguards and rear guards will have to be fitted to all outfits operating at over 32.5 tonnes. Any semi-trailer with a plated gross weight exceeding 26 tonnes must have sideguards fitted and this also applies to existing vehicles which are upplated.
The guards, both side and rear, will have to be fitted to all new trailers and semi-trailers with an unladen weight exceeding 1.02 tonnes completed on or after May 1, 1983 but there will be no retrospective requirement for rear guards to be fitted to existing vehicles. In extending the scope of the safety package, all new lorries over 3.5 tonnes which are completed on or after October 1, 1983 and first used on or after April 1, 1984 will also need side and rear guards. This includes foreign vehicles, including trailers being hauled by British tractive units.
Strength limit reduced The original requirement for sideguards circulated earlier in the year has been clarified and relaxed in certain areas. The aim of the sideguards is to protect pedestrians and cyclists who might otherwise fall under the side of the vehicle and be run over by the rear wheels. A laudable aim but one which did not explain the high impact requirement of the original proposals.
When the proposed amendment to the C and U Regs were published in March, the sideguard was required to withstand a force of 10kN over a flat area of 400sqcm. In old Imperial units, this 10kN figure is equivalent to about one ton. It was also required to withstand this impact "without deformation", in contrast to the various rear guards already in existence which dissipated the energy of an impact by deforming gradually.
The new Regulations have been sensibly relaxed. The sideguards will have to be strong enough to withstand a force of 2 kN equivalent to about 200kg (440Ib) and they are now permitted to deflect by up to 150mm (5.9in) in general although this is tightened up to not more than 30mm (1.2in) deflection within 250mm (9.8in) of the rear edge of the guard. The DTp says that this extra rigidity at the rear is to ensure that pedestrians or cyclists are pushed out of the path of the rear wheels.
Exemptions It is likely that there will be a considerable number of excep tions to the sideguard requirement. The DTp has recognised that there are particular problems in fitting such guards to tankers for example, particularly frameless ones. Thus the Department has issued a cautious partial exemption which will allow tankers to comply with the sideguard requirements "only so far as is practicable."
Other exemptions will include fire engines and military vehicles. Rather surprisingly perhaps, tippers and tractive units are also exempted. Both types are by definition short wheelbase chassis but this nevertheless represents a big relaxation in the original requirement.
Apart from these exceptions, sideguards must be fitted to any rigid vehicle (or drawbar trailer) where "the distance between the centres of any two consecutive axles exceeds 3m (9ft 10in)". Note the official wording: the definition "wheelbase" is not used as this frequently causes confusion with six and eight-wheelers.
For semi-trailers, the side guard requirement applies where the distance from the centre line of the king pin (in its rearmost position if there is any alternative) to the centre line of the nearest axle exceeds 4.5m (14ft 9i n).
To prevent anyone rolling underneath the sideguard the maximum clearance permitted is 550mm (21.6in). At the rear of the guard, the maximum gap between guard and the tyre has been set at 300mm (11.8in).
Who should fit the guards, ie, chassis manufacturer or bodybuilder, has not been defined although the Regulations do give exemption to vehicles being driven to the bodybuilder for such guards to be fitted so there is no specific requirement for the chassis manufacturer to comply.
No drawbars The drawbar outfit has been specifically excluded from the 38-tonne club and will continue to be restricted to its current 32.5-tonne limit. This, clearly, was to prevent a swing away from tractive unit/semi-trailer combinations to drawbar outfits with their extra platform length as this would have meant an effective increase in overall length from 15.5m to 18m (50ft 10in to 59ft) — something which would, in the DTp's view, have contradicted the "heavier does not mean bigger" argument.
No oldies One other restriction to running at higher weights which appears for the first time is that tractive units must have been first used on or after April 1, 1973. This is to exclude vehicles which may not conform to current noise and smoke requirements, but is not likely to prove a serious restriction to most operators.