The ratchet tie downs are the assembly of webbing and ratcheting buckle , it’s a well known fact, when the ratchet buckle is replaced by cam buckle then you get the cam buckle straps. Most likely these cam buckle straps are used on pick up trucks or passenger cars for luggage tie down, and small cam buckle(1”) are more popular than big ones(2”). Compare to cam buckle the ratchets are stronger and more widely used, the available sizes of ratchets are 1”,2”,3” and 4”, and the ratchet buckle generally has higher working load limit than the cam buckle, they have working load limit of 3,333lbs, 5,400lbs and 5,400lbs respectively, these assemblies have design factor of 3:1, thus the minimum breaking strength is 10,000lbs, 16,200lbs and 16,200lbs respectively.
Of course what we discussed above is mainly for flatbed trucks and some other kind of vehicles, there are another category of ratchet straps for semi trailers, ratchet e track straps , these tie down devices will be used with E Tracks installed inside the semi trailer. By estimation, there are almost 80% trucks on the road are box trucks, so these e track straps are supposed to the most popular ones by volume. And these straps are not as strong as the one we use on flatbed truck, the working load limit of typical e track straps is 1,000lbs, with minimum breaking strength of 3,000lbs. the low working load limit of e track straps stems from box truck wall provides support for the loads inside the truck, come to think of it, the loads won’t fall off the bed, not going to roll over, it’s much safer than the cargo out there on the flatbeds, therefore low strength tie downs can be used to secure the loads. Coupled with e track cargo bar, rope tie off, e track hardware(such as D ring with E fitting), shoring beam, e track tie downs can be used to secure any kind of loads, and secure them reliably, but you still have to pay close attention to the safety of your cargo, easy to secure is not an excuse for careless tie down practice.
We already discussed the design factor of ratchet straps, it is 3:1 and for the record all this says is that safe load limit of tie down straps is 1/3 of it’s breaking strength, for comparison purpose we know that the binder chain has a design factor of 4:1, which basically says that for the chains the working load limit will be 1/4 of their breaking strength, which indicates that tie down chains are designed for tougher environment than tie down straps are in. Nylon and polyester webbing are used in making tie down webbing, for different applications people will choose different material accordingly. Nylon webbing has better elongation than polyester, so for shock absorption wise nylon is ideal material while polyester usually is used to make tie downs for heavy equipment. Following watch list is essential for making tie down webbing, abrasion, elongation, breaking strength and use environment. There are mandated criteria for breaking strength and elongation of the tie down strap, while the abrasion and environment are mostly estimation and subjective sometimes, different area may have different requirements. Therefore the manufacturer may have to make these tie downs to different standards.