Harbor freight 4x8 stretch to 6x10

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Harbor freight 4x8 stretch to 6x10

Postby thesaltydog24 » Sun Mar 27, 2016 8:30 pm

Ok here's the deal and what I am working with. I have two 4x8 1720lbs trailers and frame members to a third that I can use to combine into one super trailer. I have seen where people have stretched the frame Length wise but what about wide. I realize I would have to purchase a new wider axle, but has anyone tried widening a HF trailer? I was thinking of using a side rail overlapping a center rail cut in half to stretch out the trailer 2 feet wider.
Any thoughts? I already have the trailer parts so basically they will be just used as building material to build a super HF trailer :lol:
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Re: Harbor freight 4x8 stretch to 6x10

Postby daveesl77 » Mon Mar 28, 2016 10:03 am

This family built a 6x10 on a standard HF trailer frame and it is what convinced me that there would be no problem with my build at 5' 6" x 9' exterior floor size, with max overall dimensions of 5' 6" w x 10' long x 5' 6" tall (exterior). This is their video and they have a website too.



I did my floor base different than they did, you can see it in my build journal and gallery. I way, way overbuilt it, but with that design I could have easily gone 6x10 on the floor. This is my video.



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Re: Harbor freight 4x8 stretch to 6x10

Postby thesaltydog24 » Tue Mar 29, 2016 6:52 am

Is there a rule of thumb on how far of an over hang over the wheels you can go? Would 7 feet wide camper body be pushing it for a 4 foot wide frame? I was planing on stretching the frame to 6 feet and building out to 7 feet, but if I can safely build out a foot and a half on each side then that would save some time and added expenses. Granted I would have to build some type of supporting structure under the floor to support the weight. Does anyone know the total width of the HF trailer from outside fender edge to other side outside fender edge. If not I can measure the display at work.
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Re: Harbor freight 4x8 stretch to 6x10

Postby daveesl77 » Tue Mar 29, 2016 8:26 am

Personally, I would not extend 18" past the frame width (going 7' wide). Mine is very stable at 9", but unless you are planning on increasing the axle width, an 18" overhang at highway speeds probably isn't the most stable of builds. The trailer sides will be well beyond the width of the tow vehicle which will dramatically increase drag. There may be someone here that has done that wide before, so they would have more knowledge on the absolutes than I.

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Re: Harbor freight 4x8 stretch to 6x10

Postby Andrew Herrick » Tue Oct 04, 2016 10:40 am

Disclaimer: I would not but a 6x10 build on a 4x8 trailer due to overloaded weight, trailer balance and aerodynamic issues, but if you go forward:

- You've probably already planned for this, but you'll need to build your floor subframe out of 2x4's rather than 2x2's. Use pressure-treated wood. Secure with lag bolts, not deck screws. Or it sounds like you might be planning to weld on extra members, which could work too :)
- Upgrade to ST-rated 12- or 13-inch tires with a Load C rating. Also, if you build wheel wells, you have to allow space to change the tire in the future. You'd be surprised how many people miss this :R
- Do some math before you build to make sure 10% of your trailer weight will be on the tongue. If you extend the trailer towards the rear, you're almost certainly to off-balance it. If you extend it towards the front, you'll risk crushing your trailer if you jackknife.
- Limit the maximum vertical drop of the teardrop rear. That will improve its aerodynamic stability.

I'm curious, though: Two Super Heavy-Duty HF trailers, what, about $700? You can get a brand new 6x10 utility trailer for $1000. Maybe it's worth the extra $300 in exchange for your saved labor and higher quality parts?
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Re: Harbor freight 4x8 stretch to 6x10

Postby bobhenry » Tue Oct 04, 2016 11:53 am

CHUBBY IS 5'6" X 10'

Found an old junk handrail and the rest is history...........Image

Bunch more pics in the very back of my album !
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Re: Harbor freight 4x8 stretch to 6x10

Postby Andrew Herrick » Tue Oct 04, 2016 4:12 pm

bobhenry wrote:CHUBBY IS 5'6" X 10'

Found an old junk handrail and the rest is history...........Image

Bunch more pics in the very back of my album !


Bob, I've seen and admired a lot of your work, but how did you build a trailer that large and still keep under the rated weight for the springs, axles and tires? :shock: The floor alone has to weigh 200 pounds ...

Plus, isn't the axle on your trailer a lot farther back than on a typical 4x8 Harbor Freight trailer? Also, If you don't extend the axle width, lateral load transfer is gonna dump a whole lot of extra weight on a tire when cornering quickly. I doubt it will make it fail, but it will shorten tire life.

Lots of people may disagree with me, and that's okay! :) Different perspectives. I guess, since you already have the trailers, you gotta figure out a way, right? :) That's the teardrop spirit! So I say just buy a 2,200-lb axle and relocate it towards the rear of the camper (you'll probably want new spring hangers), get ST-rated tires, and if you can, beef up the tongue. That'll take care of the structure, I think :thinking:
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Re: Harbor freight 4x8 stretch to 6x10

Postby Camp4Life » Tue Oct 04, 2016 4:39 pm

Technically, on a load carrying trailer which will move at highway speeds, you should never extend the load carrying frame past the track width. The track width is the center of the tire, or approximately the hub face. This is why all cargo and utility trailers have their frames within the tires, with a few having walls lined up with the track width.

What happens when you extend the frame past the hubs, is that you exert downward force outside the track width, using the tires as a fulcrum. You might think that it's ok because the other side sticks out as well so it balances out. This is all fine when the trailer is sitting level and not moving. But when you apply lateral force on the trailer, ie; taking a turn, or getting hit by a side wind, the trailer tilts to one side, and now you have the weight outside of the track width adding to that imbalance because of the weight that's being exerted outside of the track width. The further out you're extended, the worse it gets. It's the same concept as basic leverage.

Another thing to consider is how tall the trailer is because again, the taller the trailer, the more leverage that higher center of mass has, which again, makes the leverage outside the track width even worse once again. And, how heavy the weight of the walls are is also a factor, as in, do you have cabinets or a bed frame tied into the walls? Are the walls supporting much weight? The more the walls support, the more weight goes on the edge of the frame. If your trailer is built to have most of it's weight directly on the floor, then you might have a bit less of an issue then.

I know that we're not carrying 5000lb loads or anything, it's just something to think about when you want to extend a frame's width. In your case, I wouldn't be concerned extending the frame out a foot on each end as long as the trailer shell isn't taller than it is wide.
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Re: Harbor freight 4x8 stretch to 6x10

Postby KCStudly » Thu Oct 06, 2016 3:18 pm

Camp4Life wrote:What happens when you extend the frame past the hubs, is that you exert downward force outside the track width, using the tires as a fulcrum. You might think that it's ok because the other side sticks out as well so it balances out. This is all fine when the trailer is sitting level and not moving. But when you apply lateral force on the trailer, ie; taking a turn, or getting hit by a side wind, the trailer tilts to one side, and now you have the weight outside of the track width adding to that imbalance because of the weight that's being exerted outside of the track width. The further out you're extended, the worse it gets. It's the same concept as basic leverage.

I respectfully disagree with this suspicious analysis and bold sweeping conclusion. If the loads can be estimated with reasonable accuracy, a moment diagram can be solved and that would determine if the trailer will tip or not. Same for the wind statement.

The only two reaction points (if we ignore the hitch for simplicity) are the tires, so that is the only place where "downward force" can be transmitted. In a stable body, statics, loads are directional and lines of force travel along structural axes as tension or compression. In a moment diagram/calculation, symmetrical loads will be offsetting. That's just how it works; the sum of the forces trying to rotate... yada, yada. It's the non-symmetrical loads (wind/centripetal/lateral/traversing uneven ground) and the CG above the ground that matter. (For side hill scenarios we could also get into traction and coefficients of friction, soil analysis, etc.; but let's not.)

The big question is what are the loads and what are the operating conditions. A trailer OEM can't control where the end user ends up putting the load, or what terrain they drive on, so they must design for that factor. That, to me, is a more likely reasoning for why you don't see too many UT's or CT's built much past the outer side wall of the tire. There is also a matter of useful space (ergonomics) and economics of manufacturing.

Look at any semi or deck-over trailer. They all have side walls/decks that or slightly past the outside of the tires.

So I say, if the OP wants to build over the tires, so be it; just analyze the estimated loads, do some math and see if it still makes sense first. If that is beyond their capabilities, then there is always the option of emulating somebody else (many people) who has taken this approach and been successful. If this "doesn't fit in" a particular person's "box", then maybe play it more conservatively rather than less.
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Re: Harbor freight 4x8 stretch to 6x10

Postby aggie79 » Fri Oct 07, 2016 8:24 am

Andrew Herrick wrote:Disclaimer: I would not but a 6x10 build on a 4x8 trailer due to overloaded weight, trailer balance and aerodynamic issues, but if you go forward:

- You've probably already planned for this, but you'll need to build your floor subframe out of 2x4's rather than 2x2's. Use pressure-treated wood. Secure with lag bolts, not deck screws. Or it sounds like you might be planning to weld on extra members, which could work too :)
- Upgrade to ST-rated 12- or 13-inch tires with a Load C rating. Also, if you build wheel wells, you have to allow space to change the tire in the future. You'd be surprised how many people miss this :R
- Do some math before you build to make sure 10% of your trailer weight will be on the tongue. If you extend the trailer towards the rear, you're almost certainly to off-balance it. If you extend it towards the front, you'll risk crushing your trailer if you jackknife.
- Limit the maximum vertical drop of the teardrop rear. That will improve its aerodynamic stability.

I'm curious, though: Two Super Heavy-Duty HF trailers, what, about $700? You can get a brand new 6x10 utility trailer for $1000. Maybe it's worth the extra $300 in exchange for your saved labor and higher quality parts?


Although I think the comments were well-intended, I am going to respectfully disagree with the above.

Take a look at this design for a semi-standy trailer with a 10' body length, 6'-6" body width, 6' body height built on a near stock 4' x 8' HF trailer: http://tnttt.com/Design_Library/The%20Wanderer%208%20and%2010.htm. It uses the stock HF axle and tires. The floor is 1/2" plywood. The only floor framing is a 1x6 at the front and rear of the floor.

The trailer was designed by Andrew Gibbons. Andrew has designed a plethora of boats, teardrop trailers, tiny travel trailers, motorcycles, etc. Many of his designs have been constructed by TNTTT members. He put together the Excel spreadsheet for axle placement and tongue loading and design.
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Re: Harbor freight 4x8 stretch to 6x10

Postby Camp4Life » Fri Oct 07, 2016 8:58 am

KCStudly wrote:
Camp4Life wrote:What happens when you extend the frame past the hubs, is that you exert downward force outside the track width, using the tires as a fulcrum. You might think that it's ok because the other side sticks out as well so it balances out. This is all fine when the trailer is sitting level and not moving. But when you apply lateral force on the trailer, ie; taking a turn, or getting hit by a side wind, the trailer tilts to one side, and now you have the weight outside of the track width adding to that imbalance because of the weight that's being exerted outside of the track width. The further out you're extended, the worse it gets. It's the same concept as basic leverage.

I respectfully disagree with this suspicious analysis and bold sweeping conclusion. If the loads can be estimated with reasonable accuracy, a moment diagram can be solved and that would determine if the trailer will tip or not. Same for the wind statement.

The only two reaction points (if we ignore the hitch for simplicity) are the tires, so that is the only place where "downward force" can be transmitted. In a stable body, statics, loads are directional and lines of force travel along structural axes as tension or compression. In a moment diagram/calculation, symmetrical loads will be offsetting. That's just how it works; the sum of the forces trying to rotate... yada, yada. It's the non-symmetrical loads (wind/centripetal/lateral/traversing uneven ground) and the CG above the ground that matter. (For side hill scenarios we could also get into traction and coefficients of friction, soil analysis, etc.; but let's not.)

The big question is what are the loads and what are the operating conditions. A trailer OEM can't control where the end user ends up putting the load, or what terrain they drive on, so they must design for that factor. That, to me, is a more likely reasoning for why you don't see too many UT's or CT's built much past the outer side wall of the tire. There is also a matter of useful space (ergonomics) and economics of manufacturing.

Look at any semi or deck-over trailer. They all have side walls/decks that or slightly past the outside of the tires.

So I say, if the OP wants to build over the tires, so be it; just analyze the estimated loads, do some math and see if it still makes sense first. If that is beyond their capabilities, then there is always the option of emulating somebody else (many people) who has taken this approach and been successful. If this "doesn't fit in" a particular person's "box", then maybe play it more conservatively rather than less.


Then we agree to disagree. Without knowing the overall dimensions and weight distribution factors, you can't say that it's ok to overhang the frame by several feet. He said it'll be a "super trailer", which leads me to believe it'll be larger than just a teardrop. He never said how tall it will be, or if it has a rooftop AC unit, or storage rack on the roof etc... Or what if it's ultralight but top heavy? We don't know. I do agree that everything needs to be planned and estimated before modifying the frame, but you can't just say yes when you don't know the whole story. If someone asks if a 5000lb trailer is enough to carry a vehicle, you can't just say yes... is the vehicle an ATV? A small car? An F-350 SuperDuty diesel truck?
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Re: Harbor freight 4x8 stretch to 6x10

Postby KCStudly » Fri Oct 07, 2016 9:46 am

You are correct. He did say that he was considering making the trailer 2 ft wider using the stock side rail overlapping a center (xmbr?) rail and a wider axle, so I guess I misinterpreted that as building two foot wider with a 1 ft overhang. This has been done quite successfully many times before using stock tires and axle.

So it would seem that we both may have wandered off topic slightly, maybe.

For a 6 ft wide trailer with wider axle, probably the more important thing to consider is overall width. Max is 102 inches (8ft 6). With trailer tires and a typical 10 inch wide fenders that shouldn't be a problem, but wide mirrors will most likely be needed.
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Re: Harbor freight 4x8 stretch to 6x10

Postby Andrew Herrick » Fri Oct 07, 2016 11:48 pm

aggie79 wrote:Take a look at this design for a semi-standy trailer with a 10' body length, 6'-6" body width, 6' body height built on a near stock 4' x 8' HF trailer: http://tnttt.com/Design_Library/The%20Wanderer%208%20and%2010.htm. It uses the stock HF axle and tires. The floor is 1/2" plywood. The only floor framing is a 1x6 at the front and rear of the floor.

The trailer was designed by Andrew Gibbons. Andrew has designed a plethora of boats, teardrop trailers, tiny travel trailers, motorcycles, etc. Many of his designs have been constructed by TNTTT members. He put together the Excel spreadsheet for axle placement and tongue loading and design.


Now, this is a good conversation we got going here! Thanks to Aggie79, Camp4Life and KCStudly for their thoughtful replies. Wonderful to hear from your expertise.

The issue of load transfer has already been explained by KCStudly and Camp4Life. However, I think it's worth pointing out that although a moment diagram could predict whether or not the teardrop would tip at a certain angular acceleration, it doesn't consider tire wear. Trailer owners, let's face it, habitually run their trailers with underinflated tires, which over-flexes the sidewall leading to heat generation and premature failure. So if you've built a 1,400-lb trailer on a 1,700-lb capacity Harbor Freight trailer, where each tire is rated for about 1,000 pounds, a combination of load transfer and underinflation could easily overwhelm the tire. Is this a catastrophic failure? Eh, maybe not. But maybe not negligible either.

I did check out The Wanderer. Clever design. And I think there's a lot to take away from it, such as the 1x6 floor framing. I did go through the Excel chart, too. Now, I haven't built one, so I can't speak to actual numbers ... but those weight estimates struck me as pretty darn lenient for general builders. For one thing, the "fit out" estimate of 300 pounds suffices for a barebones model, but one with windows, 12/120-volt electrical system (a battery alone is 50 pounds!), cabinetry hardware, trim, seals, bedding, kitchenware, any plumbing, etc.? That's pushing it, even for a basic model. The chart also assumes a Spartan woody build. As soon as you add aluminum siding, roofing and trim, you're at the chassis weight limit. And some people would feel that his design choices - 1/4-inch sidewall sheathing, 1/2-inch flooring, 1x2 roof spars - were unacceptable structural compromises.

Now, I'm not knocking this guy's one design! He explains very clearly that if you change anything, you better make sure you know what you're doing! So If he built a 6x10 on a 4x8 trailer for 1,400 pounds, then I applaud him and his work. But I don't think it's fair to use his example as cart blanche for everyone else. There's no room for error. You can't build a 6x10 on a 4x8 kit trailer unless you're willing to mimic his design or build another barebones model. The gentleman who began this thread did not seem to have a no-frills build in mind. And I think the Wanderer 10 more-or-less proves that trying to build a 10'-long model is not something to be taken lightly, nor will it work for everybody.

And that's the end of my sermon :R Thank you all so much for your contribution! Learned a lot :D
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