The working load limit (WLL) represents the amount of weight or force that that particular piece of equipment can handle safely, without the risk of it failing. This is always a set weight and is calculated from the minimum break strength, known as a Safety or Design Factor.
| Tow Strap MBS | Safety Factor | WLL (2:1) | WLL (3:1) | WLL (5:1) |
|---|---|---|---|---|
| 100,000 lbs | Safety Factor = MBS ÷ WLL | 50,000 lbs | 33,300 lbs | 20,000 lbs |
| 200,000 lbs | Safety Factor = MBS ÷ WLL | 100,000 lbs | 66,600 lbs | 40,000 lbs |
| 300,000 lbs | Safety Factor = MBS ÷ WLL | 150,000 lbs | 100,000 lbs | 60,000 lbs |
Working Load Limit (WLL) Safety Factor
- 90,000 lb tow strap with a Safety Factor of 3 = 30,000 lb minimum breaking strength
- 250,000 lb tow strap with a Safety Factor of 5 = 50,000 lb minimum breaking strength
This enables users to make sure the equipment they use is operated within a safe range, minimizing the risk of failing, especially important in industries where they are lifting and moving highly valuable machinery, or equipment.
However, as helpful as this is, this method can not be accurately determined with tow straps or recovery straps, and we believe that indicating a WLL will almost certainly lead to serious issues for users, both in terms of reliability and safety.
Where the Confusion Lies
When carrying out a towing or recovery task, it's very easy to determine the gross vehicle weight, as this is shown in various locations on all types of vehicles. But this is not a true reflection of how much weight, or force is applied to the strap during different types of recoveries.
If you take the same vehicle, one could be stuck on loose gravel. Another might be stuck on a beach with soft, dry sand. A third could be on a beach in winter, where the sand is harder but holds water under the surface.
Finally, the vehicle might be stuck on an off-road track or field, where its wheels, axles, and brakes have sunk deep into wet, suctioned mud.
In such cases, there is physically no way to accurately calculate the amount of resistance each of these vehicles faces.
If each were to use the same strap, one or two of them would likely succeed, but the others would either be unsuccessful in their attempts or more likely experience strap failure.
This is why at Dawnerz, we focus solely on the minimum breaking strength and do not provide working load limits. We provide a range of information and resources to our customers, to provide them with enough knowledge to determine what type of strap suits them the best.
Case Study
We have two clients who both operate the same types of vehicles, and both run their vehicles fully loaded 90% of the time. However the first company operates its fleet mainly on construction sites, even though the roads are unsurfaced, they have a solid base to operate on.
So when they do experience issues in winter, it's usually in soft snow and ice, which creates mainly loss of traction. They have our 200,000 lb tow strap in every vehicle and have experienced no issues with this capacity.
However, our second customer operates in forestry and woodland, and in the winter months, the ground there is much more difficult to operate on. It's uneven, their vehicles can sink deeper at one side than the other, and the ground is much softer, causing an increased amount of resistance to recover.
This company used the same 200,000 lb tow strap, but it failed within a week. They upgraded and now carry both our 260,000 lb and 380,000 lb tow straps, and in 18 months of operations, they have experienced no further issues.
Their drivers then can evaluate the severity of each situation, and select the strap they think will best suit this specific task.
If you are unsure of how to choose the best tow strap, or are unsure about lengths, and capacities, our team is always here to assist you through the process.
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