Effective winching requires an understanding of the mechanics involved in winching. There are four main factors which influence resistance of motion when winching. These are:

• The resitance to movement of the vehicle
• The vehicle's weight
• The surface over which the vehicle will be winched
• The angle of the gradient up which the vehicle will be winched

At the end of this discussion are two examples, one for winching a Jeep up a sand dune , and another for winching a Hummer out of clinging clay .

This is influenced by the state of the tyres (inflated/deflated), friction in the drive-train, and vehicle weight. Winching is easier on normally-inflated tyres as flat tyres add additional drag.

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This refers to the gross vehicle mass, which includes passengers, baggage, fuel load and anything else aboard the vehicle when winching takes place.

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This is the largest variable when winching. A vehicle in good running condition on a hard, level tarmac surface will only require a force of about 4% of its total weight to induce motion. A vehicle to be recovered from a bog will, however, require a pull equivalent to about 50% of the total weight of the vehicle. The table in the sidebar shows that different kinds of surfaces require proportionate efforts to induce vehicle motion.

A simple formula can be used to show that approximate rolling resistance of a vehicle in good condition on a flat surface can be predicted.

Using this formula in the example that follows, we calculate the effort required to move a vehicle weighing about 4500lbs along a flat beach of hard, wet sand (which has a resistance factor of 1/6):

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Obviously not all surfaces are flat, and the steeper the surface, the greater the effort required to move the vehicle. The calculation must therefore include the gradient resistance co-efficient.

Typically, the gradient will only be of a short distance, such as a ditch or rock, or it may be of a longer distance, such as a long climb up a hill. Even for a relatively short pull, gradient resistance must be taken into account. For practical purposes, gradient resistance can be taken as 1/60th of the weight of the vehicle for each degree of the slope, up to a 45-degree incline.

Based on this formula, on a 15-degree slope, gradient resitance will be 15/60 of the weight of the vehicle, which is 1/4 of the total vehicle weight. That the slope to be negotiated to all intents and purposes is only 1ft high makes no difference to the calculations, and should be borne in mind when pulling vehicles over ridges. Consequently, if we combine the weight of the vehicle, the type of surface to be traversed and the gradient to be overcome we need to use the following calculation:

The final winching formula therefore looks like this:

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In the first example we'll winch an unladen Jeep Wrangler TJ up a sand dune of dry, loose sand with an incline of 15 degrees. Using the winching formula from above, we get the following:

Using these figures, we now have:

So in this case 1692 Lb. of effort is required to pull an unladen Jeep Wrangler up a 15 degree slope covered with soft, dry sand.

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In the second example we'll winch an unladen Hummer up a 32-degree slope of clinging clay. Again using the winching formula from above, we get the following:

Using these figures, we now have:

7041 Lb. of effort is required to winch the Hummer out of the clay. As you can see, the winching effort increases exponentially with the severity of the gradient.