you can use an equalising strap – often called a
bridle strap – which allows you to connect the
two points at a junction to the main recovery
line. This effectively halves the load each point
has to take up and distributes the load/force
across a wider area, which may minimise any
chassis twist or damage. This method works best
when tackling a straight-line recovery, because once
you’re recovering on an angle, the load distribution
- or share – across the two recovery points is altered, with
one under more load than the other. Also take into account that
the equalising strap is being loaded from its ‘side’ rather than in
a straight line from its end, which may affect the effective load
rating of the strap.
“If you were to use some sort of bridle strap – if it’s made out of
some sort of plasma or Dyneema-style rope – the load rating on
that rope is generally done on a straight-line pull,” Steve Sampson
said. “So if you’re using that as a bridle strap, the load point
actually then becomes as a side pull on that particular rope.
“Realistically, when you’re stuck in mud or whatever, it’s
pretty rare that you’ll have a 100 per cent dead-straight pull, so
the load would be very hard to distribute half-and-half on those
two points.”
A rear recovery is often needed to extract a vehicle, but when
it comes to a rear recovery point the best (often only) recovery
point available is the towbar hitch (not the towball). Adam Craze
explained: “Although we normally concentrate on designing front
recovery points, a rear recovery point is just as important. In most
cases a (rated) recovery hitch in a towbar is a safe and acceptable
point to use. A towball is not ever – never ever – acceptable to use
as a recovery point.”
In terms of rated rear recovery hitches, Adam explained the
rating must always come from the lowest rated part involved – in
the case of an Ironman 4x4 rear recovery, a hitch rating of 4.75-
tonne (as opposed to the company’s minimum 5-tonne rating for a
front recovery point). This also applies to front recovery points and
all the implements involved.
WHY WOULDN’T YOU?
THE recovery point is a relatively basic accessory when it
comes to fitment and maintenance, despite the huge amount of
engineering and design time involved. This takes into account
a vehicle’s chassis strength, maintaining the load rating even
at maximum angle of recovery (usually based on the maximum
wheel angle of the vehicle), air-bag compliance, and its near-
bombproof build (plate steel and high-tensile bolts). This doesn’t
mean you just fit and leave it, as the recovery point, like all fitted
accessories, needs to be regularly checked to ensure it’s still
correctly fitted and there’s no sign of fatigue or damage.
The relatively straightforward fitment process and ease of
maintenance, tied in with the simple fact they’re an essential for
anyone considering venturing off-road, means there is really no
reason not to fit rated recovery points to your vehicle ... and there
are way too many reasons why you should.
THE POWER OF FORCE
SO, HOW much force and load is involved in a vehicle
recovery? Well, that’s a very difficult question to answer
due to the nature of recovery situations. Each recovery
situation is unique and will contain a number of variables:
the weight of both the bogged/stuck vehicle and the
recovery vehicle; the substance the vehicle is stuck in
(mud will add much more suction force to the recovery
compared to sand); whether either vehicle is on an incline/
decline; and whether the tyres on the bogged vehicle are
inflated and/or are at any particular angle. Adam Craze
added: “As Newton states, the force is equal to the weight,
multiplied by acceleration”, with all of these affected by
the above.
Having said that, controlled tests have been conducted
that measured force in a particular recovery situation.
One such test was undertaken by the late, highly regarded
4x4 journalist Ian Glover, in conjunction with Mitsubishi
Motors Australia Limited (MMAL), to test/check for any
potential distortion in the then-current Pajero’s monocoque
chassis during a recovery. This test involved using a stock
Pajero stuck in relatively soft, shallow sand (just under the
sill). The 4x4 was subjected to a straight-line pull snatch
recovery on level ground and then a recovery on an incline.
The MMAL engineers used a load meter to record the
load in kilonewtons (kN) through the snatch strap via a
‘strain gauge’ (attached to a plate metal block on the meter
that stretched under load) to a laptop on-board the vehicle.
The load recorded for a straight-on (no angle) recovery
on a flat surface was 2.06-tonne (20.6Kn) – an ‘ideal
scenario’ in terms of a snatch recovery.
The second recovery was undertaken with the Pajero
bogged on a short incline (less sand depth than the level
location, but the wheels again pointed straight-on), and
the recovery vehicle snatched the bogged Paj forward and
over the incline. The figure recorded in this scenario was
3.16 tonne (31.6Kn), showing how factors such as gravity/
incline influence load on the recovery points, shackles and
the snatch strap.
This also explains the high load rating figures on
aftermarket recovery points, snatch straps and shackles –
and why you should fit and use them.THANKS
fellas
Thanks to Adam Craze
(www.ironman4x4.com),
Steve Sampson (www.arb.
com.au) and Troy Schipper
(www.roadsafe.com.au)
for their assistance with
this feature story.THERE’S REALLY NO
REASON NOT TO FIT
RATED RECOVERY POINTS
1566 http://www.4X4australia.com.auTECH RECOVERY POINTS