How this calculator works
A recovery winch must overcome the resistance between the vehicle and the ground plus any slope. The ground factor accounts for how deep the wheels are sunk and how much friction the surface adds, while the slope term adds the component of weight along the hill. Multiplying the vehicle weight by the combined factor gives the pull. A safety factor then sizes the winch above that pull so it is not working at its limit. For a rolled-over load, the page uses a simple moment balance: the pull needed at the attachment height is the weight times the centre of gravity height divided by the attachment height. Both models are planning estimates, not a substitute for a recovery assessment on site.
Formula
Pull on a slope = mass x g x (ground factor + sin slope angle), with g = 9.80665 m/s^2. Recommended rating = pull x safety factor. Righting pull = mass x g x centre of gravity height / attachment height.
Worked example
A 2,000 kg vehicle on grass, facing a 7.5 degree uphill pull, has a combined factor of 1.15 + sin 7.5 = 1.2805. The pull is 2,000 x 9.80665 x 1.2805 = 25.1 kN, so a 1.5 safety factor calls for about 37.7 kN of winch rating.
Advertisement
Frequently asked questions
What do the ground factors mean?
They are multipliers on the vehicle weight representing rolling resistance and the suction or friction of being bogged. Hard road is close to 1, grass and gravel are a little higher, and deeply bogged vehicles need three or four times their weight.
Is a 1.5 safety factor enough?
It is a common starting point, but a dynamic recovery can load a winch well above the static pull. Use a higher factor for a heavy vehicle, a steep pull or a winch that will be operated near its limit, and follow the winch maker's rating.
Why does the calculator not ask about wheels or tyres?
The ground factor already bundles surface and bogging effects. Wheel condition changes the real resistance, so treat the result as an estimate and allow extra margin for a vehicle with damaged or missing wheels.
Can I use it for a horizontal pull with no slope?
Yes. Set the slope to 0 to 15 degrees and use the ground factor for a mostly level pull, or read the table for the surface you are on. Remember that accelerating the load, snatch recovery and side pulls can require more than the static estimate.