Axle Load Calculator
Tongue weight does not simply add to the rear axle. Because the hitch sits behind the rear axle, it works as a lever: it puts more than its own weight on the rear and physically lifts weight off the front. A typical 840 pound tongue on a 145 inch wheelbase adds around 1,120 pounds to the rear and removes 280 from the front, which is where the vague steering and longer stopping distances come from. This calculator works out both axle loads and checks each against its own rating.
- Over an axle rating
- Front 3,105 · Rear 3,935 lb Against GAWR of 3,900 front and 3,900 rear
- Rear axle
- 3,935 lb 35 lb OVER the rating — the rear is usually the first limit reached
- Front axle
- 3,105 lb 95 lb LIGHTER than unloaded. Less weight on the steering axle means less grip for steering and braking.
- Tongue weight leverage
- +1,118 rear / -278 front 840 lb at the hitch, 48" behind the rear axle on a 145" wheelbase. It puts 278 lb MORE than its own weight on the rear and takes 278 lb off the front.
- Weight distribution
- 44% front / 56% rear An unloaded pickup is typically around 60/40. Below about 45% on the front, steering feel and wet braking degrade noticeably.
- Total vehicle weight
- 7,040 lb Compare against GVWR separately — passing GVWR does not mean both axles pass.
The lever, in numbers
The rear axle is a fulcrum. Weight applied behind it pushes down on the rear and lifts the front, exactly as it would on a see-saw, and the arithmetic is a straightforward moment balance.
Take a tongue weight of W applied at distance H behind the rear axle, on a wheelbase of L. Taking moments about the front axle, the rear axle load increases by W × (L + H) ÷ L. Because that is more than W, the difference has to come from somewhere — and it comes off the front axle, which loses W × H ÷ L.
With 840 pounds at 48 inches behind the axle on a 145 inch wheelbase, the rear gains 1,118 pounds and the front loses 278. The truck has gained 840 pounds in total, but the distribution changed by nearly three times that.
Two things make it worse. A longer overhang increases H directly — which is why extended hitches and bike racks behind the ball are consequential rather than convenient. A shorter wheelbase reduces L, which is why the same trailer behind a short-bed truck lightens the front end more than behind a long-bed.
Why a light front axle is dangerous
Steering and most braking happen at the front tyres, and both depend on the load pressing those tyres into the road. Remove several hundred pounds and you have reduced the grip available exactly where you need it.
The first symptom is vague steering — the truck wanders and requires constant correction, which drivers usually attribute to the trailer pushing rather than to the front end being unloaded.
The second is longer stopping distances. Front brakes do sixty to seventy percent of the work on a car and more on a loaded truck, and a lightly loaded front tyre reaches its friction limit sooner. ABS engages earlier, which feels like the system working but means grip has run out.
The third appears in the wet and in emergency manoeuvres, when the margin was needed and was not there. This is the failure mode that does not show up in normal driving, which is why it is rarely connected to the hitch.
A drop below about forty-five percent on the front axle is the point where experienced drivers report the handling change becoming obvious.
What a weight distribution hitch actually does
A weight distribution hitch is widely described as increasing towing capacity. It does not. Every rating on the vehicle is unchanged.
What it does is undo the lever. Spring bars run from the hitch head back to brackets on the trailer A-frame, and tensioning them applies a moment that opposes the one the tongue weight created. Some of the load transfers forward onto the front axle and some transfers back onto the trailer axles.
A correctly adjusted setup restores the front axle to close to its unloaded weight — the usual target is returning it to within a small percentage of the reading before the trailer was connected, measured on a scale.
Over-tensioning is possible and unhelpful: it can unload the rear axle and reduce traction on a rear-wheel-drive truck, and it stresses the trailer frame. The adjustment is made by scale readings rather than by feel.
Most manufacturers require one above a tongue weight threshold, often 500 pounds. That requirement exists precisely because of the effect this calculator shows.
What this is based on
- Static moment balance about the front and rear axles
- Vehicle certification label (door jamb) — GVWR and front/rear GAWR
An estimate from the figures you enter. Cab load is assumed to act midway between the axles, which is an approximation. A CAT scale reading is definitive and inexpensive — use one before relying on marginal numbers.
Frequently asked questions
Why does tongue weight lift the front axle?
Because the hitch is behind the rear axle, which acts as a fulcrum. Push down behind it and the far end — the front of the truck — rises. The rear axle carries the tongue weight plus whatever it levers off the front, which is why it gains more than the tongue actually weighs.
What is GAWR and how is it different from GVWR?
Gross Axle Weight Rating limits one axle; Gross Vehicle Weight Rating limits the whole vehicle. You can be comfortably under GVWR and still be over the rear GAWR, because GVWR says nothing about where the weight sits. Both appear on the door jamb label.
Is a light front axle actually dangerous?
It degrades the things you need in an emergency. Steering and most braking effort happen at the front tyres, and both depend on the load pressing them into the road. Take several hundred pounds off and the truck understeers, stops longer, and triggers ABS earlier in the wet.
Does a weight distribution hitch change my ratings?
No. GVWR, GAWR and payload are fixed. What the hitch does is redistribute tongue weight forward onto the front axle and back onto the trailer axles, restoring the balance the leverage took away. That is a handling fix, not a capacity increase.
How do I get my actual axle weights?
A CAT scale at a truck stop gives steer axle, drive axle and trailer weights separately for a few dollars. Weigh loaded and ready to travel — that single measurement replaces every estimate on this page.