Choosing the correct tow rope size isn't an exact science since not every piece of equipment will be stuck the same way twice. There are several factors, such as pulling angle (incline or decline), suction, depth, rolling weight vs. stuck weight, etc. Taking all of this in to consideration it is always a good idea to have a bit of a safety factor when choosing the correct tow rope. We always recommend that you choose a rope with a strength 2 to 2.5 times the weight of what you're trying to pull. For example, if you have a piece of equipment that is 40,000 lbs, a good choice would be our 1-1/2" rope, since it has a breaking strength of 90,000 lbs.
Conversely, you want to be sure to not get a rope that is TOO big for what you're pulling. If you have a 20,000 lb truck that you need to pull, a 2-1/4" rope rated at 150,000 lbs would be a bit overkill. The issue you run in to when you go too big is that you can't really utilize the "bungee effect" you get with our double braid tow ropes. If you don't have enough weight on the ropes they will start to feel more like a steel cable when you pull rather than a rope, as you won't have enough weight to give it some stretch. Keep this in mind when choosing your rope! As far as end of rope hardware goes (shackles, hooks, etc), you want to choose one is stronger than the breaking strength of your rope. A big no-no is choosing hardware with a lower breaking strength, which is putting your weak component at the end of the rope. In the instance of overloading, you never want your end hardware to fail before your rope. Nobody wants a 17 ton shackle flying through the air! We always recommend that you put some sort of weight on the body of your tow rope, such as an old tire, to force the rope downward if it were to be overloaded and break.
All of our Crosby shackles will have a "working load" marked on them, that would be the "lifting weight" that they can handle. The ultimate breaking strength of these shackles is 6 times the working load, so "working load x 6" for Crosby shackles will help you match the correct hardware! And there you have it! A little bit of math and some common sense will keep you safe and productive!