Single axle or tandem trailer?
 

I found a trailer builder that will build me whatever I want and Ive been tossing around the idea of having him install a single axle on a 7x16 mini toyhauler. Not mainly because its less rolling resistance, but because the trailer is designed for forest service roads or the yukon highway and if I encounter a big rock or washed out gully, I don't want to bend a axle if I unload one axle, and place the entire load on the other.

But like I mentioned, I'm undecided if I want two 5K axles or one 9K. But with either, the leaf springs will have to be cut down or de-leafed because total weight will be less than 75% of the rating. I'm also considering airbags and maybe a panhard bar with trailing arms.

But I am also wondering how much less rolling resistance does a single axle trailer have over a tandem with the same weight and size. Is it more significant than I imagine? And would I regret losing more stable tandem handling characteristics on the highway compared to a single axle?

I think aerodynamics would have more impact on mpg, but I don't want a gooseneck because of the risk of contact with the truck bed when on uneven terrain.

Thanks!

Goose necks kill aero and add hundreds of pounds of weight to the trailer.
Goose necks are mostly for when you just have crazy tongue weight all the time or when balancing the load isn't an option.

Ive found more than one example of people going from bumper pull to
5er with better mpg. Or bumper pull to heavier 5er with same mpg.

The air has a harder time getting between the truck and trailer since its closer.

You talking on things like campers?

My question is why you're wanting a 9K axle on a trailer that it sounds like will only weigh in at around 2-3K loaded (based on your 75% comment.) A higher rated axle will be heavier, more expensive, and require more expensive tires and likely have brakes involved, which would be unnecessary for a 2-3K load.

I will also note: I have a 6K bumper pull camper, and I would never have another bumper pull that heavy. Anything that you lose in efficiency because of the extra weight in a goose neck is made up for in being easier on the pickup: All the load is on the rear side of my springs, and it causes a LOT of flex to the pickup that wouldn't be there if the load was centered on the axle as with a 5th wheel or goose neck. Ideally 10% of your trailers weight will be tongue weight, and generally speaking most bumper hitches (whether actually on the bumper, or a receiver type) are specked to a 200 lb tongue weight. I can say from experience that they will handle more than that, but it's not great to have so much disproportional loading on your rear springs.

Of course I pull this trailer with an F150, so it truly is too much for that pickups hitch rating, but if you figure for a 600 lb tongue load in the center of the axle, I would be well within it's axle and spring load rating, though still over on the GVWR of ~6500.

I would base my axle choice on your tow rig. Use an axle or axles that use the same wheel and tire you run on your truck. Probably one 7k pound axle will use a 16” wheel with your bolt pattern. A straight axle will also provide ground clearance but you will need longer ramps to unload the “toys”.

If you offroad a lot, have them flip the axle so it's below the spring. Gives you 3" more ground clearance. The only advantage to dual axles is when you blow a tire at highway speeds you may still have something under the trailer holding it up while you pull over & stop. Tire drag would be the least important issue.

Yes. I used to have a 7000# featherlite toyhauler with all the amenities I towed with a cummins van and got 15 mpg average. It was sweet and I regret selling both, but it was to big to pull where I want to go and I need 4x4.

I talked to a couple who drove the Yukon trail pulling a bigfoot fiberglass camper. They bent both axles, so I don't want to screw around.

I'm guessing the new 7x16 toyhauler dry will weigh around 3k. Then loaded down with a finished interior, a couple motorcycles and tools and as much glamping gear I can cram in there. Then 100 gallon shower water tank which wont be full, usually.. A 20 gallon drinking water tank. All that crap might weigh 5k so I'm up to 8k or about 75% of capacity which might ride rough.. Hence de-leafing, but this is all speculation. Weight might add up quicker than I think. Maybe it will ride great as is, but I'm thinking I want longer leaf springs if using a single axle, or something to help the ride..

Exactly.. But the offset of truck rims, mine being 17", is a little more than the centered trailer rims I think so the tires would be to close to the wheel wells or rub. Plus the truck center hole is smaller than the trailer rim center hole. Two hurdles.. And are trailer studs 9/16"? Walter at Jensen trailers said he would use wheels I supply but I haven't figured out how, or how large to enlarge the center hole.

I'll use a straight axle. But using trailing arms/panhard bar with airbags or longer leafs would be nice.

Blowing a tire is definitely a concern. Especially since this is a narrow track trailer, meaning no fenders, and the wheels are under it in wheel wells. So, a 7' wide trailer that's over 8' tall? Yeah, I think you just convinced me to use tandem axles. But that limits what type of suspension I use to the stock 2' leaf springs.

The "gap" between the TV and Trailer is responsible for about 25% of the drag of the combo. Possibly this is the area that would yield the most mileage gain. Also no surprise, this would be the most complicated because of the articulation and clearance.

I don't think anybody has answered the question. Not is 1 or 2 axles better for towing, but does 2 axles and 4 tires have say twice the rolling resistance of 1 axle and 2 tires? I wouldn't think twice as much as they will be carrying 1/2 the load and can be done with lower mass axles, wheels, and tires compared to a single heavy duty axle, wheels, and tires. It will be more though but any of this is small compared to potential aero drag of what you put on the trailer, or the huge hit you get crawling around off road even without a trailer.

Your problem is not knowing how to use a weight distribution hitch. A 6k travel trailer isn’t hard to tow. It’s the trailer DESIGN that matters, not the weight.

The only 5’er advantage is aero when all is correct. They’re lousy to tow.

An aero all-aluminum travel trailer has no peer for stability and ease of use. It’s all downhill in performance from there.

To the OP. We hauled tandem and tridem goosenecks into the oilfield. Torsion axles are best choice, never leaf. The problem is approach angle; hanging the trailer on front or rear. Personally, I’d never choose single — too much weight on two tires, and poor tracking stability — but you know your situation.