Hey all,
I've been doing a lot of research on recovery straps in preparation for an off-roading trip next year. I would like to take a little bit to explain what my experience has been with straps and also share the results of my research.
I think we can all agree that you NEVER use cables or chains like you would a strap, those are for winching ONLY. 20-30 years ago, before synthetic straps were a reality, chains and cables were used this way, but would have a used tire in the linkage or something similar so you had some shock dampening in the line.
Strap/Rope Stiffness
With respect to modern synthetic straps, the common mantra of vehicle recovery is to use "Recovery" straps not "Tow" Straps. But what actually defines a tow strap vs. a recovery strap?
Most off-road forum posters will have you believe that a tow strap doesn't stretch, but a recovery strap will. This relates to materials; the most common are nylon and polyester. Polyester is much stiffer than nylon. A nylon strap will give ~20% stretch at ultimate load. A nylon rope, because the weave is different than a strap, will give ~30% stretch at ultimate load. And polyester straps will stretch ~2-3% at ultimate load. So if we take the above definition to be true, recovery straps are nylon and tow straps are polyester.
However, my straps (http://www.harborfreight.com/9000-lb-capacity-3-in-x-30-ft-heavy-duty-recovery-strap-60579.html) are branded as recovery straps, but are Polyester, and ProMark offroad's article on the matter (http://blog.promarkoffroad.com/2010/12/16/recovery-straps-polyester-and-nylon/) suggests that poly recovery straps are actually more common. I believe that a strap is a strap, it has stiffness and it has a breaking strength. Whether it says tow or recovery on the package means much less to your off-roading recovery experience than understanding the properties of the strap and using it properly.
When you're using impact loading to recover a vehicle (jerking on the strap) the stiffness of the strap has a dramatic effect on the sharpness of the jolt and the peak force in the strap and attachments. Simple high school mechanics tells us that as the strap gets less stiff, the force required to transfer the kinetic energy from the tow vehicle to the stuck vehicle goes down because it is distributed over a longer period of time. And the lower the force, the lower the chances are of breaking something. So it would seem that you would want to use nylon straps any time you are dealing with impact loading.
There is however, a caveat to this; the amount of stored potential energy within the strap is directly proportional to the distance it is stretched and the average force applied over that distance. So if we consider two ropes/straps, one of polyester and one of nylon with identical breaking strengths, upon failure, the nylon strap will have ~10 times the stored potential energy as the polyester strap. That energy is then used to propel the strap and anything attached to it at tremendous speed towards people, windows, tailgates, etc.
https://www.youtube.com/watch?v=K-0rUC74DBg
So upon failure, a nylon strap is massively more dangerous than a polyester strap. Do a search for accidents involving nylon rope and you’ll quickly see that. Here is one SFW non-graphic example:
http://www.msha.gov/webcasts/CoalSpring2004/Fatalsummaries/2003-c24.pdf
Having spent the last 3-4 years using my poly straps as recovery straps and jerking the crap out of them, I think that they're themselves ok so long as you understand that they are a stiff strap and therefore, you have to have some experience in knowing how hard you can yank on them before you start breaking things.
When to Use Which
An experienced off-roader will have both types of strap available because they should be used in separate and distinctly different circumstances.
There are three mechanisms used to deliver force to free the stuck vehicle, an Anchor, Traction, and Momentum.
Using an Anchor (tree/rock/land anchor) means that you are winching, which means a static pull. As we're not concerned with impact loading here, it is most appropriate to use a poly strap where necessary to extend the reach of the winch. This is so that the strap won't snap back as violently if it breaks.
When using the pull-out vehicle's Traction only, this again is a static pull (simply using the vehicle's wheels rather than the winch to deliver the force) and a poly strap is appropriate.
When there is absolutely no traction available (compacted snow, ice, mud) for the pull-out vehicle to use and there is nothing around to anchor to, you must use the momentum of the pull-out vehicle. This requires a strap that will stretch because the pullout vehicle will need to build up speed to make up for its lack of traction.
In my experience, the most common situation however is when you have good traction on the pull-out vehicle, but the stuck vehicle has dug a hole and is sitting on axles/frame such that a static traction pull is not quite enough. In this case a "small" tug will pull the stuck vehicle back far enough that the tires start to rise up out of the hole and raise the frame/axles off of the compacted snow/mud after which traction takes over. In this case, a poly strap is still appropriate. How deep the hole is and how far the axles/frame have dug in, will dictate the point at which this method will break the strap and should be abandoned for winching/digging. Experience will tell you when you need to do this; you'll eventually break a strap and know where that limit is, and if you've selected your equipment correctly, you won't have broken your truck or yourself when that happens - see further discussion below. Even with experience, this limit is still somewhat unknown. As we don't like digging and winching takes time we all tend to push this limit in favor of convenience. It will take X lbs of force to free a stuck vehicle regardless of the stiffness of your strap. As a result a stretchy nylon strap in this situation may be more dangerous than a poly strap because of its snap back potential.
In all cases, a static pull is safer than a dynamic pull, so if you're inexperienced, stick with winching, digging, and non-impact strap applications.
In all cases, do not used damaged equipment including cut or frayed straps; even a small nick/cut in a component severely reduces its capacity.
And in all cases, use straps and connections appropriately sized for your vehicle/application.
Strap Sizing
General consensus amongst getting stuck enthusiasts is to have a strap rated for somewhere around 2-4 times the weight of your vehicle. In the case of Nylon straps or ropes, you don't want to have a capacity much more than this because the stretch rating is measured at ultimate load, so if you have a 20k 20% strap, but are only pulling 5k of force, you only have 5% stretch and you might as well be using a poly strap. With a poly-strap however, stiffness is not a concern, so getting one that is rated for more is not a problem as far as its function is concerned. However, in both cases, you want to make sure that the breaking strength of the strap is lower than the capacity of what you’re attaching it to. If something is going to break, we want the strap to break, not the weld/bolts holding the tow hooks/eyes to the frame/bumper. This prevents a steel component breaking and being propelled by the strap.
Connections
The MSHA incident above brings us to the next topic. The one place where consensus is universal is that you should never have hooked ends on your straps/ropes as they become projectiles following a failure. Closed shackles/eyes are much tougher and have higher capacity; these are the way to go. Also, their failure mode is typically more ductile than a hook so they’re more likely to bend before they break. Also,you should never use a ball hitch to attach a strap to the vehicle. The prying effect on the neck of the ball combined with the high shock load can break the ball off and send it flying like a cannon ball.
Shackles should have at least twice the "rated" capacity of the straps attached. That way you can use the link in a snatch block configuration, or with multiple straps in a straight pull. The "rated" capacity of a strap is the tested breaking strength of the strap in new condition. The working load limit "WLL" is limited by DOT to no more than 1/3 of the rated strength. It is important to know the difference when sizing your connections and attachments. To prevent steel projectiles, we want the strap to be the fuse in the system.
When connecting two straps in series, loop the straps together without a shackle as shown here:
http://www.driveoffroad.com/media/wysiwyg/recovery-09.jpg
The stick helps prevent the knot from becoming impossible to undo.
Conclusion
The bottom line is that you should understand what your equipment is capable of and use it in accordance with this knowledge.
I hope this will settle some of the vehement and seemingly uneducated arguing I've seen on the matter (Not here obviously). Feel free to weigh in if you see something wrong or missing.
I've been doing a lot of research on recovery straps in preparation for an off-roading trip next year. I would like to take a little bit to explain what my experience has been with straps and also share the results of my research.
I think we can all agree that you NEVER use cables or chains like you would a strap, those are for winching ONLY. 20-30 years ago, before synthetic straps were a reality, chains and cables were used this way, but would have a used tire in the linkage or something similar so you had some shock dampening in the line.
Strap/Rope Stiffness
With respect to modern synthetic straps, the common mantra of vehicle recovery is to use "Recovery" straps not "Tow" Straps. But what actually defines a tow strap vs. a recovery strap?
Most off-road forum posters will have you believe that a tow strap doesn't stretch, but a recovery strap will. This relates to materials; the most common are nylon and polyester. Polyester is much stiffer than nylon. A nylon strap will give ~20% stretch at ultimate load. A nylon rope, because the weave is different than a strap, will give ~30% stretch at ultimate load. And polyester straps will stretch ~2-3% at ultimate load. So if we take the above definition to be true, recovery straps are nylon and tow straps are polyester.
However, my straps (http://www.harborfreight.com/9000-lb-capacity-3-in-x-30-ft-heavy-duty-recovery-strap-60579.html) are branded as recovery straps, but are Polyester, and ProMark offroad's article on the matter (http://blog.promarkoffroad.com/2010/12/16/recovery-straps-polyester-and-nylon/) suggests that poly recovery straps are actually more common. I believe that a strap is a strap, it has stiffness and it has a breaking strength. Whether it says tow or recovery on the package means much less to your off-roading recovery experience than understanding the properties of the strap and using it properly.
When you're using impact loading to recover a vehicle (jerking on the strap) the stiffness of the strap has a dramatic effect on the sharpness of the jolt and the peak force in the strap and attachments. Simple high school mechanics tells us that as the strap gets less stiff, the force required to transfer the kinetic energy from the tow vehicle to the stuck vehicle goes down because it is distributed over a longer period of time. And the lower the force, the lower the chances are of breaking something. So it would seem that you would want to use nylon straps any time you are dealing with impact loading.
There is however, a caveat to this; the amount of stored potential energy within the strap is directly proportional to the distance it is stretched and the average force applied over that distance. So if we consider two ropes/straps, one of polyester and one of nylon with identical breaking strengths, upon failure, the nylon strap will have ~10 times the stored potential energy as the polyester strap. That energy is then used to propel the strap and anything attached to it at tremendous speed towards people, windows, tailgates, etc.
https://www.youtube.com/watch?v=K-0rUC74DBg
So upon failure, a nylon strap is massively more dangerous than a polyester strap. Do a search for accidents involving nylon rope and you’ll quickly see that. Here is one SFW non-graphic example:
http://www.msha.gov/webcasts/CoalSpring2004/Fatalsummaries/2003-c24.pdf
Having spent the last 3-4 years using my poly straps as recovery straps and jerking the crap out of them, I think that they're themselves ok so long as you understand that they are a stiff strap and therefore, you have to have some experience in knowing how hard you can yank on them before you start breaking things.
When to Use Which
An experienced off-roader will have both types of strap available because they should be used in separate and distinctly different circumstances.
There are three mechanisms used to deliver force to free the stuck vehicle, an Anchor, Traction, and Momentum.
Using an Anchor (tree/rock/land anchor) means that you are winching, which means a static pull. As we're not concerned with impact loading here, it is most appropriate to use a poly strap where necessary to extend the reach of the winch. This is so that the strap won't snap back as violently if it breaks.
When using the pull-out vehicle's Traction only, this again is a static pull (simply using the vehicle's wheels rather than the winch to deliver the force) and a poly strap is appropriate.
When there is absolutely no traction available (compacted snow, ice, mud) for the pull-out vehicle to use and there is nothing around to anchor to, you must use the momentum of the pull-out vehicle. This requires a strap that will stretch because the pullout vehicle will need to build up speed to make up for its lack of traction.
In my experience, the most common situation however is when you have good traction on the pull-out vehicle, but the stuck vehicle has dug a hole and is sitting on axles/frame such that a static traction pull is not quite enough. In this case a "small" tug will pull the stuck vehicle back far enough that the tires start to rise up out of the hole and raise the frame/axles off of the compacted snow/mud after which traction takes over. In this case, a poly strap is still appropriate. How deep the hole is and how far the axles/frame have dug in, will dictate the point at which this method will break the strap and should be abandoned for winching/digging. Experience will tell you when you need to do this; you'll eventually break a strap and know where that limit is, and if you've selected your equipment correctly, you won't have broken your truck or yourself when that happens - see further discussion below. Even with experience, this limit is still somewhat unknown. As we don't like digging and winching takes time we all tend to push this limit in favor of convenience. It will take X lbs of force to free a stuck vehicle regardless of the stiffness of your strap. As a result a stretchy nylon strap in this situation may be more dangerous than a poly strap because of its snap back potential.
In all cases, a static pull is safer than a dynamic pull, so if you're inexperienced, stick with winching, digging, and non-impact strap applications.
In all cases, do not used damaged equipment including cut or frayed straps; even a small nick/cut in a component severely reduces its capacity.
And in all cases, use straps and connections appropriately sized for your vehicle/application.
Strap Sizing
General consensus amongst getting stuck enthusiasts is to have a strap rated for somewhere around 2-4 times the weight of your vehicle. In the case of Nylon straps or ropes, you don't want to have a capacity much more than this because the stretch rating is measured at ultimate load, so if you have a 20k 20% strap, but are only pulling 5k of force, you only have 5% stretch and you might as well be using a poly strap. With a poly-strap however, stiffness is not a concern, so getting one that is rated for more is not a problem as far as its function is concerned. However, in both cases, you want to make sure that the breaking strength of the strap is lower than the capacity of what you’re attaching it to. If something is going to break, we want the strap to break, not the weld/bolts holding the tow hooks/eyes to the frame/bumper. This prevents a steel component breaking and being propelled by the strap.
Connections
The MSHA incident above brings us to the next topic. The one place where consensus is universal is that you should never have hooked ends on your straps/ropes as they become projectiles following a failure. Closed shackles/eyes are much tougher and have higher capacity; these are the way to go. Also, their failure mode is typically more ductile than a hook so they’re more likely to bend before they break. Also,you should never use a ball hitch to attach a strap to the vehicle. The prying effect on the neck of the ball combined with the high shock load can break the ball off and send it flying like a cannon ball.
Shackles should have at least twice the "rated" capacity of the straps attached. That way you can use the link in a snatch block configuration, or with multiple straps in a straight pull. The "rated" capacity of a strap is the tested breaking strength of the strap in new condition. The working load limit "WLL" is limited by DOT to no more than 1/3 of the rated strength. It is important to know the difference when sizing your connections and attachments. To prevent steel projectiles, we want the strap to be the fuse in the system.
When connecting two straps in series, loop the straps together without a shackle as shown here:
http://www.driveoffroad.com/media/wysiwyg/recovery-09.jpg
The stick helps prevent the knot from becoming impossible to undo.
Conclusion
The bottom line is that you should understand what your equipment is capable of and use it in accordance with this knowledge.
I hope this will settle some of the vehement and seemingly uneducated arguing I've seen on the matter (Not here obviously). Feel free to weigh in if you see something wrong or missing.
