The Fact about Ratchet Straps
We all know that when put ratchet buckle and tie down webbing together we get ratchet strap, 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”). 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, the typical working load limit for 2” tie downs is 3,333lbs, for 3” and 4” which is 5,400lbs, since these tie downs have design factor of 3:1, the minimum tensile strength is 10,000lbs and 16,200lbs.
So far we discussed about tie down devices for flatbeds or similar commercial vehicles, we will see there are other kind of trucks, the typical one is box truck, and most of them have E Tracks installed inside the truck, for these rigs we use e track straps. In fact semi trailer 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.
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 most common materials in making tie down webbing are nylon and polyester, which serve different tie down applications. The typical application for nylon webbing is motorcycle tie down, while polyester webbing is ideal for tying down concrete pipes. Elongation, tensile strength, abrasion and environment, these have to be taken into consideration when making tie down strap. Breaking strength has to reach the recommendation level no matter what, and elongation has to meet the requirement, abrasion and environment sometimes are not that clear cut, when designing tie downs we may have to consider the most extreme conditions these tie down straps may be in, or we may just consider the normal transportation environment.