From Montana Overland and 4x4 and Adventures
OFF-ROADING 101: A Little Winch Math:
Basic winching and the effects of deep mud, sand, or snow on mire math.
What if your 4x4 is stuck in deep Mud? The depth of the bog (mire) will have a massive effect on the loaded weight of the vehicle being recovered. Here is a very simple guide for calculating the dead weight of the vehicle when in the mud. It's not scientific, but it is usable & easy to remember.
If stuck to the base of your wheels (known as "tire-depth"), it can require a pull of up to 75% to 100% of the loaded vehicle.
If stuck to the axles, it may require a pull of up to 150% of the weight of the stuck 4x4.
If stuck to the chassis/rocker panels+, depending on how deep, it can be 2x to 3x the total weight of the stuck vehicle! That will depend on just how deep you are stuck and the viscosity of what you are stuck in. In general, think 2x vehicle weight at the rockers and 3x if you are bogged to mid-doors. Meh...it happens. Hopefully, not very often, though.
That's a potential pull of 300% of the load. 3x an average JKU Rubi is around 18,400lbs or so. So, it is best to keep that in mind for a deeply mired rig, though mire factors of 1x to 2x will be much more common.
Of course, pulling sideways, uphill, or if there is vehicle damage will make things even worse.
Have your snatch block(s) handy, and make sure that ALL of your recovery gear is up to the task. It is good form to pull out enough winch line to use the inner, more powerful layers on the drum for best results.
Wheel Safe!!