Mar 31 2011
Ratchet Tie Down Straps Explained
The well known fact is that the assembly of strap webbing and ratchet buckle usually called ratchet tie down, if we use cam buckle instead of ratchet buckle then it’s cam buckle tie down, it’s pretty straight forward, isn’t it? 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, the typical safe 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 breaking strength is 10,000lbs and 16,200lbs.
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 strap , these tie down equipment will be used with E Tracks installed inside the semi trailer. It is estimated that 80% trucks are box trucks, and the e track tie down system is just for semi trailers , so e track straps are most popular tie down straps. 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 easy to understand that why e track straps are not as strong as regular ratchet tie down straps, inside the box truck the loads already have strong support, at least there is no risk of falling off, all the e track straps will do is to fixate the loads more than tie them down.
As we discussed in the first paragraph, the design factor of ratchet assembly is 3:1, that means the working load limit is 1/3 of the minimum breaking strength, while binder chains which have a design factor of 4:1, that means the transport chains will work in more tough environment than tie down straps, which usually are chose for regular loads. 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. 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 down 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.











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