Recovery Force & Drawbar Pull Guide: How to Size a Recovery Tow Strap

When a vehicle or piece of heavy equipment gets stuck, choosing the right recovery tow strap isn't as simple as matching the strap's rating to the vehicle's weight.

A 30,000 lb machine does not just require 30,000 lb of pulling force to recover it. Mud, soft ground, slopes, locked wheels and other conditions can add significant resistance.

At the same time, the recovery vehicle may be capable of generating considerably more force than is actually required to free the stuck machine.

That's why there are two numbers you need to establish before sizing the recovery system:

1. How much force is estimated to be required to free the stuck vehicle?
2. How much pulling force can the recovery vehicle potentially generate?

The first helps identify the required recovery force.

The second determines the maximum force the recovery system may be subjected to.

Both matter when selecting a recovery strap and connecting hardware.

1. Calculate the Estimated Recovery Force

Start with the GVW (Gross Vehicle Weight) of the stuck vehicle or equipment.

Then account for additional resistance created by the recovery conditions.

The basic calculation:

Estimated Recovery Force = GVW + Additional Resistances

Additional resistance can come from:

• Mud or soft ground

• Slopes

• Locked or seized wheels

• Other conditions that increase resistance during the recovery

The factors below provide a way to estimate those additional loads.

Start With the Actual GVW

Determine the Gross Vehicle Weight (GVW) of the vehicle or equipment at the time of recovery.

Use the actual loaded weight, including any cargo, attachments, equipment or other significant weight being carried.

For example:

Actual GVW = 30,000 lb

That 30,000 lb is the starting weight for the calculation. You then apply the appropriate resistance factors for the recovery conditions.

You do not add the vehicle's weight, cargo or attachments separately, they are already accounted for in the GVW.

Add Resistance From the Recovery Conditions

Mud & Soft Ground

Soft ground can significantly increase the resistance a vehicle needs to overcome.

Use the appropriate resistance factor based on the recovery conditions:

Surface Resistance

GVW × Resistance Factor = Surface Resistance

For example, a 30,000 lb machine in light to moderate mud:

30,000 × 0.33 = 9,900 lb

So the mud adds an estimated:

9,900 lb of additional resistance

Slope

A slope creates additional resistance because the recovery vehicle must overcome the force acting against the vehicle's movement.

Use the appropriate slope factor:

Slope Resistance

GVW × Slope Factor = Slope Resistance

For a 30,000 lb machine on a 10° slope:

30,000 × 0.17 = 5,100 lb

The slope therefore adds an estimated:

5,100 lb of resistance

Between two values?

If the actual slope falls between two listed values, round up to the next listed factor.

Locked or Seized Wheels

Locked or seized wheels can add significant resistance because the vehicle cannot roll normally during the recovery.

Use the applicable factor:

Locked-Wheel Resistance

GVW × Resistance Factor = Additional Resistance

Only include this factor when the recovery conditions actually require it.

Calculate the Estimated Recovery Force

Once you've identified the applicable resistance factors, add them to the vehicle's GVW.

Formula

Estimated Recovery Force = GVW + Surface Resistance + Slope Resistance + Additional Wheel Resistance

Only include the resistance factors that apply to the recovery.

Example: 30,000 lb Machine

Let's say a 30,000 lb machine is stuck in light to moderate mud on a 10° slope.

GVW

30,000 lb

Mud

30,000 × 0.33 = 9,900 lb

Slope

30,000 × 0.17 = 5,100 lb

Estimated Recovery Force

30,000 + 9,900 + 5,100 =

45,000 lb

The estimated force required to free the machine is therefore:

45,000 lb

But we're not finished.

There's another number that matters when selecting the recovery equipment.

2. Check the Recovery Vehicle's Pulling Power

We've calculated an estimated recovery force of:

45,000 lb

If we used that figure to size the recovery strap at 3:1, we would need:

45,000 × 3 = 135,000 lb MBS

But does that figure match the drawbar pull or rim pull of the recovery vehicle?

What Is Drawbar Pull?

Drawbar pull is the maximum pulling force a vehicle or machine can generate at its drawbar. 

Let's say the recovery vehicle has a maximum drawbar pull of:

70,000 lb

That means the recovery vehicle is capable of applying up to 70,000 lb of pulling force.

So even though we estimated that the recovery would require 45,000 lb, the recovery vehicle could potentially apply considerably more.

If the recovery reaches 70,000 lb, our 135,000 lb MBS strap would have:

135,000 ÷ 70,000 = 1.93:1

The original 3:1 margin has been significantly reduced.

Check out our CAT® and John Deere® drawbar pull chart here.

3. Why Maximum Pull Matters

This is why the strap should not simply be sized around the estimated recovery force when the recovery vehicle can generate substantially more force.

If we size around the recovery vehicle's maximum potential pull:

70,000 × 3 = 210,000 lb MBS

Now, even if the recovery requires the full 70,000 lb available from the recovery vehicle, the system still has the intended 3:1 ratio.

That's the important distinction.

• 45,000 lb is what we estimate the recovery will require.
• 70,000 lb is what the recovery vehicle may be capable of applying.

If the estimate is wrong, the actual recovery force can be higher than expected.

Sizing around the maximum potential pull gives the recovery system more margin when that happens.

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Drawbar Pull Is Not Horsepower

Horsepower does not tell you how much pulling force a recovery vehicle can generate.

Horsepower describes the rate at which work can be performed. Drawbar pull describes pulling force.

Where available, use the manufacturer's maximum drawbar pull or rim-pull specification when assessing the maximum potential load on the recovery system.

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Need Help Choosing the Right Recovery Equipment?

Recovery loads aren't always straightforward. If you're unsure about the calculations, drawbar pull, MBS, WLL, or which recovery strap is right for your application, the Dawnerz team is here to help.

Tell us what you're recovering, the equipment you're using and the conditions you're working in. We'll help you understand the numbers and identify the right recovery solution for the job.

Have a question? Don't guess. Contact Dawnerz.