View Full Version : Calculating Tow hitch capacity
04-11-2012, 08:30 AM
I bought a home made bumper with a tow hitch plate for my '64 Dodge D100 pickup. The truck is rated at a 1/2 ton I believe and weighs in at around 3400 lbs.
How do I figure out the tongue weight and gross weight capacity of this setup? I'm guessing I can take the thickness of the metal, the span, etc and apply some sort of formula but I don't know where to start.
Can post pictures if needed.
04-11-2012, 09:12 AM
This is a much more involved process than just plugging the material thickness, span etc. into an equation. Not only are there shear and moment forces, then adding a big enough safety factor for hitting a pothole loaded trailed. Since you bought this "homemade" we have no way of knowing how well it was built, how it attaches to the vehicle, and since this is a welding forum, how well it was welded.
Hopefully, someone on this forum may be able to give you a ballpark figure based on past experience, though.
X2. There's a lot more to this than simply looking up a chart. Understrength materials, poor tie in to the vehicle or poor welds, could make this hitch pretty much useless. I wouldn't trust an unknown hitch with any real load.
At a blind guess, if everything was done right, I'd say it's likely a Class I or Class II hitch at best. Class 1 hitches are rated to tow trailers up to 2,000 pounds with 200 pounds of tongue weight, and Class 2 can handle 3,500 pound trailers with 350 pounds of tongue weight. Some stock bumper hitches are rated even lower, some less than 1,000 pounds with 100 pounds of tongue weight.
I don't know many guys who tow real trailers who use bumper hitches. They either use a class 3 or better frame hitch with a receiver, or frame hitches are specifically designed for towing ( usually with pintles) , like whats found on medium to heavy class trucks.
Best bet is to simply buy a Class 3 kit that fits your vehicle and bolt it on. Then you have no questions about what it will hold.
04-11-2012, 02:54 PM
Thanks for the replies. I hear what you're saying. Does anyone know how a hitch is rated Class I, Class II, etc.? I assume there must be some design, construction, and materials criteria.
It's based on how the engineer designed it.
04-11-2012, 11:46 PM
Bumper hitches don't normally match the capacity of receiver hitches.
Rated capacities, I believe, are based on vehicle manufacturers GVWR and CGVWR. A search for that information can possibly shed light on the limits that the vehicle was designed to carry and/or tow. No hitch will allow you to exceed those parameters. That said, by knowing that you have a 1/2 ton truck, an older truck, it is better to assume a realistic limit. Most pickups we fit with class 3 hitches today, in general. That is a 5,000 pound tow limit, that's according to the hitch, not the truck. If you want to show some pictures of the hitch, we can offer opinions, but that is up to you. :)
A bumper is best left to class 2 or less, (imo). I bought an after market bumper for my first truck, a '90 Dodge Dakota. I tried pulling a long trailer with that and bent the step. Then I went out and bought a receiver hitch. That only gave me a way to burn out the overdrive, so... asking too much from the truck is really bad practice. YMMV :laugh:
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