TOWCHECK FIELD GUIDE
Working Load Limit vs. Breaking Strength
Working load limit (WLL) is the maximum weight a securement component is rated to support in everyday service. Breaking strength is the force required to break the component under test conditions, typically 3 to 4 times the WLL.
What the terms mean
Working Load Limit represents the safe operating capacity defined by the manufacturer or regulations. Breaking strength (or tensile strength) is the failure threshold. WLL is calculated as a design factor fraction of breaking strength.
Worked example
Common mistakes
- Using breaking strength instead of Working Load Limit when checking securement capacity.
- Assuming the assembly rating matches the strap rating (it is governed by the weakest component, often the hook or anchor).
- Failing to account for strap wear or UV degradation which lowers both limits.
Frequently asked questions
Why is the design factor so high?
Design factors (typically 3:1 or 4:1) provide a safety margin against dynamic forces, shocks from bumps, wind resistance, and wear over time.
Is it legal to use breaking strength?
No. Federal and state cargo securement regulations strictly require calculating capacity based on Working Load Limit (WLL).
Primary references
These sources support terminology and general planning context. Use the current documentation for your exact vehicle, trailer and components.
Continue with your own numbers
Run the Complete Tow Check, use the scale worksheet, or review the calculation methodology.