The ratchet straps are just the assemblies of ratchet buckle and tie down webbing, but if we use cam buckle in place of ratchet buckle in the assembly we have cam buckle tie down, it’s as simple as that. Cam buckle tie downs are only for light duty use, and 2” cam buckles are the biggest size we will see in the real world use, and it’s still light duty. Ratchet buckles are different, there are 1” to 4” ratchets, and they can be quite heavy duty and can stand all kinds of abuse, the most commonly used on commercial trucks are 2”, 3” and 4” ratchet tie downs, 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.
Up until now all we talked about is the tie downs for flatbed or similar commercial vehicles, in reality semi trailers are much more than flatbeds in numbers, since they are box trucks the tie down needs are different, you will see most semi trailers have E Track installed and use logistic straps. In fact box truck has much bigger share than flatbed truck, the percentage maybe around 80%, of course this is only estimation but you get the idea, and the conclusion is that e tack straps are by far the most popular tie downs. The e track straps usually have working load limit of 1000lbs, which is only 30% of the 2” flatbed tie downs, and the breaking strength is only 3,000lbs based on design factor 3:1. 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 load , easy to secure is not an excuse for lousy tie down practice.
In first paragraph we talked about design factor of ratchet tie downs, which is 3:1, so the working load limit is 1/3 of maximum breaking strength for ratchet straps, 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. The standard material of which tie down webbing is made is nylon webbing or polyester webbing, depends on different tie down applications. 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. When making the webbing, we have to take following characteristics in to consideration, the breaking strength, elongation, abrasion and the environment. When making tie down strap, manufacturer has to follow the recommendation of breaking strength and elongation requirements, when it comes to abrasion and environment, there are much more variations to be considered.
