From Montana Overland and 4x4 Adventures. Off-Roading 101: A little more winch math.The effect of gradient (slope) on recovery force.We talked about the sometimes substantial mire factors of deep mud, snow, and sand, but figuring out a recovery load can involve more. If you want to move a 5700-pound Jeep on hard-pack or pavement, it really does not take much energy to do so. Moving that 5700-pound Jeep in such conditions will only take about 5% of the vehicle's weight or about 285 pounds of force. Most grown men could push that with a bit of effort.However, if we pull that same Jeep up a 15-degree gradient, we can estimate the required force to be 25% of its weight (mass). Now, it will require about 1425 pounds of force to move it, and that is on a hard, smooth surface. A 30-degree uphill pull will equal about 50% of the vehicle's mass or, in the case of our 5700-pound Jeep, about 2850 pounds of force to move. Even relatively small gravel or a soft surface, like sand, can change things pretty dramatically, too.These may not sound like large numbers alone, and by themselves, would an easy pull for the winches we commonly use. However, you will be adding these numbers to the mire factors (if any) we discussed in our previous post on "the effects of deep mud, sand, or snow on winch (mire) math." So, as an example, if my 5700-pound Jeep is bogged body deep in snow or mud, I will multiply the weight (mass) of my Jeep by 150%, or 8550 pounds. Since, in this scenario, it is also stuck on a 15-degree hill, I will need to add 25%, or 1425 pounds, to the mire numbers for pulling it up the grade. So, 8550+1425= 9975 pounds of force to move/recover. What is your winch rated at again? Let's just say this is clearly time to break out a snatch block (or two) and perform a double or triple-line pull. Your winch will thank you. Of course, pulling a vehicle downhill reduces the required force for recovery.Hopefully, the key takeaway here is simply understanding how quickly the forces required for a 4x4 recovery can add up. This knowledge empowers you to ensure your equipment and rigging method are up to the task, making your off-roading experience safer. No, you shouldn't need a graphing calculator to recover a stuck 4x4, but you do need to have a basic understanding of the forces involved. I hope this helps.Wheel Safe!!©2024 Richard Hiltz(*Don't give me any crud about newtons vs pound-force. Pounds of force will work well enough for our purposes.)
21 Badlands, 2 dr, four banger, slushbox, SAS. PERFECT!
