Tow / Recovery Strap Terminology Explained

When comparing heavy-duty tow straps and recovery straps, you will see terms such as MBS, WLL, SWL, tensile strength, breaking strength, safety factor, and elongation.

These terms are not interchangeable.

Understanding what each number and term actually means is important when selecting the right recovery strap for your vehicle or equipment.

MBS - Minimum Breaking Strength

MBS stands for Minimum Breaking Strength. It is the minimum force a strap is required to withstand before breaking when tested under the applicable test conditions.

For example, Dawnerz’s 380,000 lb tow strap has an MBS of 380,000 lbs.

MBS is a strength rating, it is not a vehicle weight rating. The MBS of a strap should never be interpreted as the maximum weight it can pull or recover.

A 380,000 lb MBS does not mean the strap is designed to recover a 380,000 lb vehicle. The appropriate strap capacity depends on the vehicle weight, recovery method, configuration, forces involved, and applicable safety factor.

WLL - Working Load Limit

WLL stands for Working Load Limit.

WLL is the maximum recommended working load for a strap under a specified application and safety factor.

For example, using a 3:1 safety factor:

100,000 lb MBS ÷ 3 = 33,333 lb WLL

Using a 5:1 safety factor:

100,000 lb MBS ÷ 5 = 20,000 lb WLL

This is why you should never look at MBS alone when determining the appropriate working capacity.

Safety Factor

The safety factor is the relationship between the breaking strength of the product and its rated working load.

For example:

• 3:1 means the working load is one-third of the MBS.

• 5:1 means the working load is one-fifth of the MBS.

The appropriate safety factor depends on the application, product type, standards being followed, and the manufacturer's specifications.

Do not simply choose a safety factor based on preference. Always use the rating and requirements applicable to the product and application.

SWL - Safe Working Load

SWL stands for Safe Working Load.

You may see SWL used interchangeably with WLL in some industries and older documentation.

However, terminology can vary between manufacturers, industries and standards.

When comparing products, always look at how the manufacturer defines the rating rather than assuming that two numbers with the same name were calculated the same way.

Tensile Strength

Tensile strength describes the ability of a material or product to withstand pulling force before failure.

It is commonly used when discussing materials such as synthetic webbing, rope, fibers and other components.

Tensile strength is a useful technical measurement, but it should not automatically be treated as the same thing as the MBS or WLL of a finished recovery tow strap.

A finished strap is a system that includes the webbing, eyes, stitching and other construction details.

Average Breaking Strength

Average Breaking Strength is the average result from a series of breaking tests.

This is different from Minimum Breaking Strength.

For example, if several straps are tested and the results vary, the average may be significantly higher than the lowest result.

That does not mean every strap will withstand the average value.

This is why minimum strength is a more meaningful number when establishing a minimum performance requirement.

Elongation

Elongation refers to how much a strap stretches when force is applied.

Synthetic straps elongate under load, which can affect how the strap behaves during a recovery.

Elongation is therefore an important characteristic of recovery equipment, but more elongation does not automatically mean a better strap.

The appropriate characteristics depend on the intended application and construction of the product.

Straight-Line Pull

Straight-line pull refers to a recovery where the tow strap is loaded generally in line with the vehicle and the attachment points.

This is the simplest loading direction and helps minimise additional forces caused by angled loading.

Side Loading

Side loading occurs when a tow strap or its attachment point is pulled at an angle rather than in a straight line.

Side loading can change the forces applied to the strap, attachment points and recovery hardware. Tow straps and connecting hardware should be used only in configurations permitted by the manufacturer's specifications.

Shock Loading

Shock loading occurs when force is applied suddenly rather than gradually.

Examples can include a sudden take-up of slack, an abrupt movement of the recovery vehicle, or a dynamic recovery. Shock loading can create forces significantly higher than the static load being applied.

This is particularly important because MBS and WLL figures should not be interpreted as permission to apply sudden or dynamic loads to a tow strap.

Conclusion

Understanding tow strap terminology makes it easier to read product specifications, compare different tow straps, and understand what the numbers actually represent.

Browse the full Heavy-Duty Tow Strap collection to compare available MBS capacities. 

 

Technical Terms & Abbreviations