Choosing Trailer Axle Capacity: Hitch Weight, GAWR, Wheels and Tires

The right axle capacity starts with what the loaded trailer weighs and how much of that weight rides on the hitch. This guide shows how to work out the load your axles carry, how a single axle compares to a tandem, and why springs, wheels and tires can limit the rating. It also lists every Dexter beam capacity Southwest Wheel offers.

Once you know the capacity, measure for the beam with How to Measure for a Custom Dexter Trailer Axle.

Key takeaway

• Axle capacity: Subtract the hitch load from the gross vehicle weight. The rest is the load on the axles.
• Hitch weight: A bumper hitch should carry 10% to 14% of the gross weight. A fifth wheel or gooseneck should carry 15% to 20%.
• GAWR: The rating at the tires is limited by the lowest rated part, including the springs, wheels and tires.
• Side to side: If the load sits off to one side, that side must not carry more than half the axle rating.

Terms you need

• GVWR (Gross Vehicle Weight Rating): The loaded weight of a single vehicle, as rated by the manufacturer.
• Hitch weight: The part of the trailer's weight that is carried on the tow vehicle through the hitch.
• GAWR (Gross Axle Weight Rating): The load carrying capacity of the axles, measured where the tires meet the ground. It includes the wheels and tires.

Step 1: Work out the load on the axles

Axle capacity is usually found by subtracting the hitch load from the gross vehicle weight. What is left is the load the axle or axles carry.

How much weight goes on the hitch

Make sure the axles, wheels and tires are matched and rated to carry the axle share. A trailer can still handle poorly if the load is piled at the front or back end, even when the hitch weight is in range.

Hitch classes by trailer weight

The Dexter guide also lists the SAE classes for ball and coupler hitches by trailer gross weight, and the two SAE application types for pintle hooks by vertical hitch load:

Watch side-to-side loading

If the load is shifted off center to one side, the wheels on that side carry more. The load on the heavier side must not be more than half the rated capacity of the axle or axles.

Step 2: Place the axles under the load

Where the axles sit decides how the weight splits between the hitch and the axles:

1. Measure from the center of the hitch to the trailer's center of gravity.
2. Divide that by the share of the load the axles will carry.
3. The result is the distance from the center of the hitch back to the center of the axle set. On a tandem, that is the center of the hanger.

Example: the center of gravity is 135" behind the hitch, and you want the axles to carry 90% on a bumper hitch. 135 divided by 0.90 is 150", so the center of the axle set goes 150" behind the hitch. The hitch then carries 15 divided by 150, or 10%.

Step 3: Check the GAWR

A beam rating is not the whole story. The GAWR of the running gear is based on its lowest rated part.

The Dexter guide gives this example: an axle beam rated for 6,000 lb., springs rated for 2,500 lb. each, wheels rated for 3,500 lb. each and tires rated for 3,042 lb. each. The GAWR is 5,000 lb., limited by the two springs.

Exceeding the maximum overhang printed on a beam's page also reduces the axle's capacity. See How to Measure for a Custom Dexter Trailer Axle for overhang.

Step 4: Match the wheels and tires

• Match the capacity: Match the wheels and tires to the axle capacity. The two wheels and tires on an axle must equal or exceed the axle capacity.
• Never put a higher rated tire on a lower rated wheel: Most people inflate and load a tire to the rating on its sidewall, which can make the wheel fail.
• Match the rim: Tires are made for specific rim sizes and contours. A mismatch is dangerous.
• Match the hub: Hub piloted wheels have a close-fit center hole and use flange nuts or a clamp ring. Stud piloted wheels have a tapered seat at each bolt hole, and the cone angle of the nut must match it.
• Drop axles: Use a wheel and tire diameter large enough that the axle parts will not drag the road if a tire goes flat.

Shop matched sets in Trailer Wheels, Tires, and Assemblies.

Single axle or tandem: a worked example

Say your loaded trailer weighs 7,000 lb. and uses a bumper hitch.

• At 10% hitch weight, the hitch carries 700 lb. and the axles carry 6,300 lb.
• At 14% hitch weight, the hitch carries 980 lb. and the axles carry 6,020 lb.

Plan for the larger number, 6,300 lb.

On a tandem, the axle ratings add up to the total. Two 3,500 lb. axles give 7,000 lb. When you place a tandem under the load, measure to the center of the hanger, not to one of the axles.

Tandem leaf spring setups often use equalizers, which help transfer load from one axle to the other as the trailer travels over uneven ground. Not every equalizer and hanger combination is suitable. If the equalizer hangers are too short, the spring eye can hit the frame as the suspension moves and overload the spring.

Also space the axles so the tires have at least 1" of clearance between them under any load. Take the tire maker's maximum tire diameter and add 1" or more to get the axle center to center distance.

Dexter recommends brakes on all axles. Commercial trailers must also meet the Federal Motor Carrier Safety Regulations, which call for brakes on each wheel for most uses.

Capacities Southwest Wheel offers

Stock Dexter standard spring beams come in 2,000, 3,500, 5,200, 7,000 and 8,000 lb. Custom built beams also come in 4,400, 6,000 and 7,200 lb.

Stock straight beams:

• 2,000 lb. standard spring beam
• 3,500 lb. standard spring beam
• 5,200 lb. standard spring beam
• 7,000 lb. standard spring beam
• 8,000 lb. standard spring beam

Custom built only:

• 4,400 lb. custom beam
• 6,000 lb. custom beam
• 7,200 lb. custom beam

Every custom capacity is in Custom Built Dexter Trailer Axles, and the full axle line is in Trailer Axles. Deciding on a drop? See Drop Axle vs Straight Axle: Deck Height Guide.

Beam listings are the beam only. Springs, hangers, U-bolts and hubs are sold separately. Pick springs, wheels and tires rated for the same capacity as the beam.

Lead time, returns and shipping on custom beams

• Lead time: Custom beams are built to order. Delivery is 2-3 weeks after the order.
• Returns: Once the order is placed, a custom axle cannot be altered, changed, cancelled, or returned for any reason.
• Shipping: Shipping is one charge for the entire order.

Axle capacity checklist

1. Loaded weight of the trailer (gross vehicle weight)
2. Hitch type: bumper (10% to 14%) or fifth wheel and gooseneck (15% to 20%)
3. Load on the axles: gross weight minus hitch weight, using the low end of the hitch range
4. Single or tandem, and the total of the axle ratings
5. Side-to-side loading: heavier side no more than half the axle rating
6. Axle set placed under the load: hitch to center of gravity, divided by the axle share
7. Springs rated for the axle capacity
8. Two wheels and tires per axle that equal or exceed the axle capacity, never a higher rated tire on a lower rated wheel
9. Overhang inside the range on the beam's page

Not sure which capacity fits your trailer? Verify fitment before ordering or call 1-800-866-3336.

Frequently asked questions

What capacity trailer axle do I need?

Subtract the hitch weight from the loaded weight of the trailer. The axles must be rated for what is left. With a bumper hitch, that is 86% to 90% of the gross weight.

What is GAWR?

Gross Axle Weight Rating, the capacity of the axles measured where the tires meet the ground. It includes the wheels and tires, and it is limited by the lowest rated part.

How much tongue (hitch) weight should a trailer have?

10% to 14% of the gross weight on a bumper hitch, and 15% to 20% on a fifth wheel or gooseneck.

Can two 3,500 lb. axles carry as much as one 7,000 lb. axle?

The ratings add up, so a tandem of two 3,500 lb. axles totals 7,000 lb. Each axle still needs springs, wheels and tires rated for 3,500 lb.

Will bigger tires raise my axle capacity?

No. The GAWR is limited by the lowest rated part. Never mount a higher rated tire on a lower rated wheel.

Do you offer 4,400, 6,000 or 7,200 lb. axles?

Yes, as custom built beams. The 4,400 lb. beam is straight only.

Can I change or return a custom axle?

No. Once the order is placed it cannot be altered, changed, cancelled, or returned.

Know your capacity? Decide between a stocked or built-to-spec beam in Custom Built vs Pre-Configured Dexter Axles: Which to Order.

Keep every part rated the same. Build a Complete Dexter Trailer Axle matches hubs, brakes, springs, wheels and tires to one capacity.

Picked your springs? Hanger Spacing for Single and Tandem Leaf Spring Axles shows where to put the hangers.

Southwest Wheel - Your Trailers Best Friend Since 1919.

References

• LIT-008-00, Dexter Axle applications guide, page 3 (Definition of Terms: GAWR, Hitch Weight), page 4 (Definition of Terms: GVWR), page 6 (Things To Consider When Designing Your Trailer), page 8 (Determining Dimensional Requirements, Brake Requirements, Wheels And Tires), page 9 (Axle Attachment Systems), page 10 (Specifying Axles), page 11 (Hitches).
• Axle Position Guidelines, revised January 1996, page 1 (Hitch, Center of Load and Center of Hanger).