The primary purpose of this calculator is to answer the question: “How heavy a fifth wheel can I tow with my truck?”
This calculator is designed for fifth wheel trailers towed by a fifth wheel hitch mounted in the bed of a truck above the rear axle.
In the form below, enter as many pieces of information as are required. The more accurate information you provide, the more accurate the calculation will be.
If you are unfamiliar with the weights or abbreviations, you may want to start with Understanding RV Weights.
Want to see some examples? Scroll to or jump below the calculator!
*ALERT!*
As of January 8, 2024, this interactive RV calculator is temporarily suspended. We apologize for the inconvenience, and we hope to have the calculator back up and running soon. In the meantime, we recommend reading through the rest of the notes on this page, which may help clarify your understanding. Thank you for visiting Changing Gears.
A Working Example
In this scenario, you know quite a bit about the truck. Also, when you go camping, you bring along a dirt bike and other equipment in the bed of the truck, adding about 800 lbs of cargo.
Because of this, the calculator found the GVW to be the most restrictive number, and reduced the maximum trailer weight accordingly.
Example, using a hypothetical truck similar to the 2005 Dodge RAM 1500, regular cab, 4×4, 5.7L HEMI Magnum V8 engine:
- Tow vehicle GVWR: 6,350 lbs
- Tow vehicle GCWR: 14,000 lbs
- Tow vehicle maximum loaded trailer weight rating: 8,900 lbs
- Tow vehicle RGAWR: 3,900 lbs
- Tow vehicle TVTW: 4,845 lbs
- Tow vehicle Cargo: 800 lbs
- King Pin Weight %: 25%
Calculated Maximum Trailer Weight: 2,220 lbs
As you can see, the calculated result of 2,220 lbs is significantly lower than the maximum specified by Dodge at 8,900 lbs!
In fact, the calculator even tells you that the GVWR is to blame. In other words, you’re maxing out your tow vehicle’s maximum allowable weight (due to payload) before anything else!
The large difference is because the manufacturer ratings use the truck weight with standard equipment and driver only. Options and cargo add to the truck weight, reducing towing capacity.
Additionally, the Dodge numbers assume a 15% king pin weight, while we assumed a more restrictive 25%.
If we slide the King Pin Weight % slider to 15%, then the maximum trailer weight jumps to 3,700 lbs.
But while the lower percentage makes it look as if you can tow more, you need to find out the actual king pin weight and percentage before settling on this number. Weigh, don’t guess!
Unpermitted Scenarios
Our calculator does not permit the below scenarios. This is why all input information is required for accurate results.
What I only know the truck’s GVWR and GCWR?
A common “mistake” – albeit one made intentionally by RV salesman and truck manufacturers – is to calculate maximum towing capacity simply by subtracting the weight of the truck from the combined vehicle weight rating.
This is a best-case scenario!
- This assumes a stripped-down tow vehicle with no mods or optional equipment, a 150-lb driver (thanks for rubbing it in, guys!) and no onboard cargo.
- This also assumes that perfect mechanical reliability and performance (yeah, right!).
- It even assumes that the trailer brakes do 100% of the RV braking work, which isn’t the case for older or unadjusted brakes.
A similar mistake, although more conservative, is to subtract the truck GVWR from the GCWR. This assumes that the truck is fully loaded, and therefore reduces the towing capacity by 1:1.
On the face of it, this looks more conservative. However, it’s NOT. A fully loaded truck – that is, when the passengers and cargo equals the payload capacity – can’t tow anything. Not a pound. Because any additional weight would overwhelm the tow vehicle GVWR!
If you only know the truck’s and , enter them into the first two boxes. Maximum trailer weight will be calculated by subtracting GVWR form GCWR.
Example, using the 2005 Dodge Ram (above):
- Tow vehicle GVWR: 6,350 lbs
- Tow vehicle GCWR: 14,000 lbs
Calculated Maximum Trailer Weight: 7,650 lbs. As we’ve learned from the calculator, this is way, way too high for the truck as actually configured!
What if I only know the hitch maximum king pin weight rating?
Another common error is to assume that the hitch weight rating of the truck is the limiting factor and to base the maximum trailer weight solely on it.
For instance:
- Maximum king pin weight = 1500 lbs
- Assumed king pin percentage = 15%
Maximum trailer weight = 10,000 lb!
This puts us well above the GCWR for virtually all half-ton trucks!
Nor does this back-of-the-envelope calculation factor in the effect of payload.
These scenarios illustrate that relying on too little information may cause you to exceed manufacturer ratings. On the other hand, providing the calculator with all relevant weight numbers will produce accurate results
