The widely acknowledged fact is that the assembly of tie down strap and ratchets usually called The ratchet straps or sometimes just called ratchets consist of hardware ratchet buckles and webbing with hooks , if we use cam buckle instead of ratchet buckle then it’s cam buckle tie down, it’s pretty straight forward, isn’t it? 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. Unlike cam buckle, ratchet buckle are much stronger, and 2”,3” and 4” ratchet buckles are used in industrial grade applications, such as heavy duty transportation, with 3,333LBS, 5,400LBS working load and a design factor of 3:1, these ratchets have 10,000LBS and 16,2000LBS breaking strength respectively, which are pretty strong for most tie down applications.
So far we talked about tie down devices for flatbeds or similar transportation 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. It’s understandable that e track straps have lower working load limit, because the box truck wall will provide strong support for the loads inside, and the truck wall will prevent the loads from falling off, rolling over, tilting and some other dangerous movements.
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. Following watch list is essential for making tie down webbing, abrasion, elongation, breaking strength and use environment. When making tie down straps , 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.