(– by Drizit #6240 –)
My theory is "bigger is better".
At minimum double the weight of the vehicle and carry a snatch block.
I'm with Wrangler on this one, the winch manufatures say 1.5x the weight of the vehicle however you must consider how they are rated. An 8000lbs winch is rated to pull an 8000lbs keep in mind those ratings are based on the last layer of rope on the spool and that doesn't last for a great deal of your pull if you even get there. Each sucessive layer you get back on reduces your pulling power by about 10% A snatch block will double your pulling power and also let you pull out twice as much line on a short pull. Reading the Warn Winching guide before you ever reach for the remote is a great idea.
Understanding just what kinds of loads you will be applying requires a bit of math but it's not that bad.
the formatting on this is much better in the PDF I advise you download it, this info comes from page 5&6
To get the best from your winch and auxiliary equipment requires some understanding of the mechanics involved in winching. For winching purposes the resistance to motion of a vehicle is dependent on five main factors.
(i) The inherent resistance to movement of the vehicle to be recovered.
(ii) The total weight of the vehicle to be recovered.
(iii) The nature of the surface to be transited by the vehicle to be recovered.
(iv) The gradient up which the vehicle to be recovered is required to be moved.
(v) Any damage sustained by the vehicle.
(i) The inherent resistance of a vehicle depends on whether the vehicle has sustained any damage to it’s rolling gear, e.g. whether all or some
of the wheels are missing or not, the state of the tyres on any remaining wheels (a flat tyre will cause considerable drag, it may be advisable to
change a tyre that is deflated before commencing recovery operations), friction in the drive-train (which will cause drag), and the weight of the
(ii) The weight of the vehicle, includes all equipment, luggage, fuel, passengers and stores, etc. aboard the vehicle.
(iii) The nature of the surface to be traversed is the second largest variable in the winching equation. A vehicle in good running order on a metalled
surface will only require a force of about 4% of its total weight to induce motion, whereas a vehicle to be recovered from a bog will require a pull
equivalent to about 50% of the total weight of the vehicle. The table below shows that different surfaces require proportionate efforts to produce
Type of Effort required to move
Surface vehicle as a fraction of total weight
Hard metalled road 1/25 total weight
Grass 1/7 total weight
Sand (hard wet) 1/6 total weight
Gravel 1/5 total weight
Sand (soft wet) 1/5 total weight
Sand (soft/dry/loose) 1/4 total weight
Shallow mud 1/3 total weight
Bog 1/2 total weight
Marsh 1/2 total weight
Clay (clinging) 1/2 total weight
A simple calculation will show that approximate rolling resistance of an undamaged vehicle on a flat surface can be predicted e.g. the pull required
to move a vehicle weighing about 2041 kgs along a flat sandy beach of hard wet sand.
Weight of vehicle (kgs) 2041 kgs
= = 340kgs
co-efficient of resistance of hard wet sand 6
However, as all surfaces are not flat, the calculation must therefore include the gradient resistance co-efficient.
(iv) Gradient Resistance. The gradient up which a vehicle is to be moved may only cover a short distance, over the total distance of the pull, e.g.
a ditch or rock, or it may cover a long climb up a hill. Even for a relatively short upward pull, gradient resistance must be taken into account. For
practical winching purposes, gradient resistance can be taken as a 1/60th weight of the vehicle for each degree of the slope, up to 45 degree
Gradient x weight of vehicle
e.g. for a 15 degree slope, gradient resistance will be 15/60 of the weight of the vehicle, which is 1/4 the vehicle weight. For an incline of 45
degrees the gradient resistance will be equal to 3/4 of the total weight of the vehicle. That the slope to be negotiated to all intents and purposes
is only 1ft high will make no difference to the calculations, and should be kept in mind when pulling vehicles up or over ridges.
(v) The damage sustained by the vehicle is the largest variable in the winching equation. The damage resistance of the vehicle to be recovered
can be expressed as:
No. of damaged wheels
Weight of Vehicle x
No. of wheels
THE THEORY OF WINCHING 02-1
THE THEORY OF WINCHING
THE THEORY OF WINCHING
Note that twin wheels count as one.
So, if no wheels are damaged on a four wheeled vehicle then there is no damage resistance to be added to the final equation. However, if all
four wheels are damaged on a four wheeled vehicle, then we must add the entire weight of the vehicle to the equation as the damage resistance.
If we combine the weight of the vehicle, the type of surface to be transited, the gradient to be overcome and the damage to the vehicle we get
Weight of Vehicle Gradient Damaged Wheels
+ x Weight of Vehicle + x Weight of Vehicle
Surface to be transited 60 Total Wheels
Therefore the winching formulae is
W (G x W) (DW x W)
+ + = effort required
S 60 TW
Where W = Weight of vehicle
S = Surface to be transited
G = Angle of gradient (in degrees)
TW = Total No. of Wheels on vehicle
DW = No. of damaged wheels on vehicle
i.e. A vehicle weighing 2041 kgs, with two non operative wheels out of four is to be recovered up a grass bank with a slope of 45 degrees.
Using the winching formula above.
Where W = 2041 kgs (vehicle weight)
S = 1/7 (co-efficient for grass)
G = 45 (slope in degrees)
DW = 2
TW = 4
2041 (45 x 2041) (2 x 2041) (91845) 4082
+ + = 292 + +
7 60 4 60 4
= 292 + 1531 + 1020
= 2843 kgs effort required to recover vehicle.
If we substitute shallow mud for the surface (co-efficient of 1/3) in the above equation we get:
2041 (45 x 2041) (2 x 2041) (91845) 4082
+ + = 680 + + = 3231 kgs effort
30 60 4 60 4
The effort required may be outside the capacity of the winch, (the rating of a winch usually refers to the first layer of wire rope on the drum). In
this case, one solution may be to run out most of the winch cable to enable the winch to be used at or near its rated capacity, or introduce a pulley
block in the winch line to create a mechanical advantage, thus reducing the effort required by the winch.