UNDERSTANDING OF REGULATION 219
THERE ARE STILL many in the Road Transport Industry,
Suppliers and Operators, who are apparently unaware that it is
no longer legal to fit an independent "Tag"
axle to a Semi-Trailer.
Road Traffic Regulation states -
semi-trailer first registered on or after 1 July 1999,
shall be fitted with only one axle or one axle unit,
which axle unit shall be fitted with suspension of one
type only, namely either air suspension, steel
suspension, or rubber suspension.
The importance of this
Regulation is that a semi-trailer can have only one axle or
one axle unit and in the case of an axle unit all the axles in
the unit must be interconnected, and reference must be
made to the definition of "Interconnected" which
- means, for the purpose of the definition of "axle
unit", the design is such that an upward force on one
axle in an axle unit transmits a downward force to the
remaining axle or axles in the axle unit.
Figure 1 illustrates
the ramifications of Regulation 219 which applies to all
semi-trailers registered for the first time after 1 July 1999.
It is important to remember that the fitting of independently
suspended "Tag" Axles, in front of or behind other
axles in an axle unit is no longer permitted, also, all
axles must be fitted with this same suspension, i.e.
conventional steel springs, air or hydraulic. This does not
mean that a semi-trailer cannot have an axle unit with the
axles positioned as illustrated on Figure 2, as it is
permissible to fit an axle unit, shown on Figure 2, providing
all the requirements prescribed in Regulation 219 are complied
with. But there are application problems.
To achieve complete interconnection of all axles with
steel/spring suspension is extremely difficult and
complicated, and if all axles are fitted with air suspension,
care must be taken to ensure that the suspension incorporates
adequate stroke (up and down).
In the case of an axle unit, as depicted on Figure 2, it is
essential that the rear most axle be a steered axle
(mechanical or self-steered) and care must be taken to ensure
that the steered axle provides adequate angle of steer.
Figure 3, shows a six axle
artic consisting of a standard 6x4 truck-tractor and a three
axle semi-trailer, as shown on Figure 3.
With the front steering wheel of the truck-tractor, the
turning radius set at 13.1 m to the outside of the outer
wheel, it will be noted that theoretically the angle of turn
is 24° but...
The maximum angle of turn of the outer wheel of available
steered axles is ± 15° when the angle of turn is prevented
trom further turning by limiting stops. This of course means
that the very purpose of the steered axle is negated.
Theoretically, when the turning radius of the outside of the
outer front wheel of the truck-tractor reaches 18.322 m, the
outside radius of the turning corridor is 18.733 m and the
inside radius 13.922 m and, most important, the turning angle
of the outer steered wheel of the semi-trailer will be 15°.
Any "tighter" turning radius will result in
"scuffing" of the tyres of the axle unit of the
For the record, the turning radius of a standard 6x4
truck-tractor is 7.5 m.
The question must be asked - "Is the three axle
semi-trailer with an axle unit, as illustrated on Figure 3,
acceptable in practice if tight turning conditions are
purpose of Regulation 219 was to include the fitting of a
steered axle to gain additional loading on Tridem
Semi-Trailers. The purpose of this Regulation is still
applicable to existing semi-trailers, but in view of the
amendment to Regulation 225 increasing the wheelbase of a
semi-trailer from 9 m to 10 m, virtually negates the advantage
gained from Regulation 219.
Regulation 219 does not apply to new semi-trailers
manufactured since the amendment to Regulation 225 on 25
September 2003 and only to the pre-existing semi-trailers.