Drop frame van RV

Are we talking about a trailer setup or a truck frame setup? Some reason I thought we were talking about customizing a truck body, but regardless, same principal applies except we're talking about the empty/laden tongue weight change versus the steer axle weight change

I used to refer to the web site below frequently in a previous life.

Trailer Weight and Balance Equations and Calculator | Engineers Edge | www.engineersedge.com

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Just buy 30ft + RV and pull a 1 or 2 car enclosed trailer, why reinvent the wheel?

 

A few thoughts:
You will want as much weight on the drive axle as possible. I pull some specelized trailers that have almost no pin weight because the axles are almost in the center of the trailer. On dry roads it is squirrely, on poor roads it’s down right ignorant.

Have you pulled a spread axle before? They pull down the road nice and straight but would be a nightmare in a camp ground. Absolutely put a dump valve on at least the rear axle if not both axles.

Are you sure the rear suspension of the truck is only rated at 17k? Seems low for a single axle?

 

There's probably not an issue with that configuration per se. But my concern would be does king pin weight get lighter as you load the trailer? Because as a toy hauler, the bulk of the weight probably gets applied behind the trailer axles. Then we get into actual expected gross laden weight. Unless we're talking about a very bizarre short trailer, as long as you have sufficient towing vehicle (1 ton tandem or bigger) weight distribution should not be an issue

Also, I don't like the idea of 3 axles either on a travel trailer, however, you are limited by readily available tire weight ratings of the appropriate size. If you're pushing the weight limits, you may need to consider 3 axles if dual configuration is not an option.

Lots of guys running the older and heavier 2-axle luxury 5th wheels of yesteryear are having problems with blowouts as the typical real-world weights of these rigs, and summer heat causes problems with 16 inch load range G tires. You see very few of the bigger "toy haulers" of today with only 2 axles. It's just too much to ask of these 4 tires under full load configuration.

 

Steve, a couple questions:
you say you're limited to 17K on your drives because of the suspension but I'm not sure that's really the case. I assume it's half a tandem that you've modified, but tandems are 34K by law, is the single-axle version really limited to 17K? I'd assume it would actually be a 20K axle because it's a single axle. You know more about your axle than I do but I'm curious and the answer would be helpful.

What's a scale ticket look like for your rig as it is? how does the rear axle scale with the trailer you currently have?

I run a somewhat similar setup, single axle tractor and single or tandem axle trailers with it. It's a day cab so I don't have experience with how a truck like yours scales with a sleeper and a single-axle, but... depending upon how much camper you install into that trailer, I can't imagine with a tandem out back you'd be hitting any sort of limits on weight. I can fit a car a and a lot of stuff into our 28' pup trailer (kentucky single drop with 19.5s) and not be even close on weight (but again, our tractor is light). How much does all the RV stuff weigh? Also, I'm not saying handling doesn't matter, but if it's not for commerce, I'd assume you can take your time getting places, and reducing speed helps handling a lot so maybe you don't need to worry so much as long as it scales.

I think one of the reasons the axles are far forward on a lot of RV trailers is for tight turns.

Just a few thoughts, questions. I've got some experience with related details, but you've got a specific set of details there.

 

For the scrubbing it depends on how many miles you're planning on getting out of a set of tires. As an RV, you may never do enough slow speed driving to scrub the tires enough for it to matter. I assume since fun is the plan, it's more about getting where you're going and enjoying yourself there than packing in 100,000 miles a year. They also make tires for high-scrub applications. If the spread axle solves problems I'd say do it and use the appropriate tire. I also don't get the idea you're strapped for cash so a set of 8 trailer tires every couple years isn't the end of the world.

Since you're doing the fabrication yourself, you could also drop $1000 and get a single portable scale. While you're mocking stuff up, you could test the weight distribution with the scale before you weld everything up finally. You'd be able to tell if just moving the tandem and minor changes to the arrangement of the goods in the trailer would be enough, or if going to a spread would do it. I've never pulled a spread axle so someone else will have to make suggestions about that. I do pull drop frames and they have a low center of gravity and ride nicely, especially if you have belly boxes and load them (maybe good for the water tanks & car spares and such).

 

Kentucky puts spreads on their race hauler trailers:
Kentucky Trailer
Kentucky Trailer