Lightweight Car Trailers

[Don-F]

Hello I was referred to this website because I'm looking for tips on open car trailer designs that don't weigh a lot.

I do not have the luxury of a dedicated tow vehicle so my Ford F150 will have to do the pulling. I designed my old trailer in 2001 to pull very light fwd cars and it did its job just fine and towed well. I wanted to go to a dual axle trailer for safety and a little more load capacity. Most real car trailers locally (West Coast USA) are either very expensive or very heavy and use a lot of iron. That was true 13 years ago and not much has changed now. I think other countries are better at designing light weight trailers for car hauling and I was hoping to add some of that wisdom to my next trailer build.

So I thought I would start by asking for some trailer design advice and critiquing the 10ft x 6ft torsion axle trailer I just sold.

Things I think I did OK:

• It used mostly 2”x3” 0.120 (50mmx75mm 3mm) tube and in 14 years it didn’t defect or crack. This is despite being over loaded horribly when borrowed by a friend.
• 0.120” (3mm) Diamond Plate for decking and limited cross members. I used the decking to hold the two 2x3 tubes on both sides together. I used almost no horizontal cross members under the plate. I only put four total, two in front of the axle and two in the rear. I positioned the horizontal cross members 12” (304mm) apart, right under the tire contact points. The rest of the area just had the area spanned by the diamond plate.
• I liked the low ride height both for loading and stability.
• I liked the hand winch a lot.
• I had a 4ft long trailer tongue. I think the length helped the short trailer tow well.
• 13" tires, keeps the trailer low and other small car trailer manufactures like Brian James use even smaller Diameters on their products.

Things I want to improve on the new trailer:

• Build an A Frame tongue under the deck and make the coupler adjustable
• Increase the length of the bed to at least 13ft (3962mm)
• Increase the width to 6.5ft (1981mm)
• Add a two 2200lb rated axles, 4400lb (1995kg) gross weight.
• Possibly switch to dropped leaf spring axles for cost and being able to service the assembly if something wears out. This will raise the deck slightly. I am having trouble finding them in the 2200 models though.
• Ramps, I didn’t like lugging them around. Maybe even design a tilt tongue.
• Maybe put the hand winch to the side like on Brian James’s newer trailers.
• Make a spare tire holder.
• Add some skid wheels to the rear of the trailer to help with dragging.

Here is my old trailer, now sold.

The basic layout of the old trailer.

This trailer design interests me. Its just a picture I found on the internet. It looks to use very small diameter tube but be using the plates on the sides as a truss to strengthen the structure.

Brian James Trailers also make very nice trailers that look like they are very light. They have been in business for many years so hopefully their designs are solid.


Thanks, Don

 

[arsco]

one car dolly and two uhaul ramps.

 

[theoldwizard1]

A couple of tips.

Diamond plate or solid decking is heavy. Use expanded metal and more braces underneath it.

Youe side rails are trusses.

Spacing another rail parallel to each side rail, like in the above pictures, adds tremendous strength. You don't need sheet metal between those 2 rails. Just triangulated pieces.

I will be surprised if you can get away with no ramps, even on a tilt bed trailer. Most cars do not have adequate clearance in front of the front tires or behind the rear tires to accommodate anything except a long ramp.

 

[kerrynzl]

Do you have access to, or somebody you can pay with a press-brake?

This trailer was folded up from 1-1/2 sheets of 12’x 5’ x 1/8” sheet steel [I built 2 at a time]
The 12’ sheet is split lengthways and then folded to make the profile needed.

I used 1 length of 3”x2” RHS for the main cross-members, and purchased a few offcuts for the winch pole / cross-member
There is no frame rails at all, the folded main runners became the frame rails.

The drawbar tongue is also folded on a pressbrake as a lipped channel.
Instead of welding a “bridge” on the tongue to stop flex, I decided to fold it as part of the integral shape [triangular].

Even though the deck is short [at 12’] , I made the tongue long [I think this is important]
The tongue extended 6’ in front of the deck giving it the behaviour characteristics of a much longer trailer .

The deck tilted on it’s own suspension , the pivots were at the rear of the tongue.
I had chains to limit the angle of the tilt, but still used simple wooden ramps because road race cars usually only have 3-4” of ground clearance

It was incredibly stable [even at 80-90mph] and never tried to steer the tow vehicle, and there was no need for a load equalizer [it never pitched over bumps]

The total weight of the trailer was 880lbs . Most cars I towed on it were 3000lbs .
With the Corvette race-car on it, the total weight was 3454lbs [ In NZ trailer brakes aren’t required until 4400lbs GVW ]
I did tow a 4800lb 4x4 on it which was scary, [not because of the engineering but because the tyres were marginal.]

This was built in 1998 and is still going strong [except paint and scratches] I sold it with my Lotus Cortina to a friend to finance a divorce.
If I was to build it again, I would use Electric brakes and a Tongue mounted controller.[ electric brakes were rare in NZ back in 1998 ]
And also fender backs to prevent rocks flicking off the tyres. Fender backs also increase the beaming strength of the trailer.

As for commercial viability, the average Kiwi “DIYer” [equivalent to your craigslist morons] equates value to the amount of materials and not the labour content or design.
They think I would sell it for next to nothing because it is “bare bones” [I don’t work for free for those dickheads]

 

[Don-F]

Great help on both posts! Thanks! I will have to see if I can find a fabricator that can bend metal at 12 or longer.

 

[fourjeepin]

RE ramps, my car hauler came with them mounted underneath. I didn't like pulling them out and sticking them in the right spot, so I cut off the brackets and used the steel to build flip down ramps. More efficient and saved weight!

 

[bert.]

those photos look like an Australian trailer pretty common design over here as most cars we tow are under 2ton

 

[kerrynzl]

those photos look like an Australian trailer pretty common design over here as most cars we tow are under 2ton

The trailer towing the HR32 skyline is made by Austrailers

 

[David Walter]

I made this trailer and it weights about 700kgs. It is built for a specific purpose, my race car so this design might suit your purpose.

 

[Don-F]

Thank you for the replies and advice. Its been very helpful. I am looking to build an open trailer at the moment, but I am stashing all the info here for future use so feel free to share more about your enclosed trailer project too. It looks like the suspension drops for loading?

 

[mark18mwm]

I have a trailer made remarkably similar to the one made by kerrynzl. It is a commercially made trailer, a Riteway, it's old a 1978 but still works great. I had used it when I raced dirt modified race cars. With a 2300 lb. car about 500 lbs of tools and parts you never knew it was even behind you. I sold the race cars but kept the trailer and still use it a lot, including to haul my 4000 lb. skid steer. I admit that is pushing the trailer kind of hard but it handles fine and so far seen no ill affects on the trailer of that weight in such a small area. If there is any doubt about using bent (pressed) sheet metal for a strong trailer mine is proof they can be incredibly strong, even when abused by large loads. The only bad thing about the thin metal is making sure to have some reinforced areas for tie downs.

 

[David Walter]

The light weight design of the trailer is possible due to the fact the enclosure structure is a stressed member. That way the floor and its frame is not required to be braced or made of thicker steel.
You are correct the trailer has drop axles and is running on air bags so it is able to load my race cars without having to raise suspension or using the wooden plank method.
If you look inside you can see the framed triangulation which give the enclosed structure the strength

 

[kerrynzl]

The light weight design of the trailer is possible due to the fact the enclosure structure is a stressed member. That way the floor and its frame is not required to be braced or made of thicker steel.
You are correct the trailer has drop axles and is running on air bags so it is able to load my race cars without having to raise suspension or using the wooden plank method.
If you look inside you can see the framed triangulation which give the enclosed structure the strength

I've been down that road mate!

If the side panels become a stressed member you don't need any triangulation at all.[ a true monocoque design ]
You can make the whole trailer from prefinished composite sign board and furniture tubing [25 x 25 x 1.2 ]
If you glue the panels to the tubing it would have greater beaming and torsional strength than any ladder frame.

The weakest point that would need strengthening is around the rear door frame.

A common problem with aluminium skin sides is ripples [especially in the sunlight if painted black ]
The secret is to preheat the aluminium with a propane heater, and leave it going while the glue sets.
Once the glue sets, turn off the heat and the aluminium cools and pulls itself arrow straight.

Don't build an enclosed trailer too lightweight [especially if you need to do a lot of miles empty] They become a nightmare to tow on windy days
[ don't ask me how I know this ]

 

[404]

The light weight design of the trailer is possible due to the fact the enclosure structure is a stressed member. That way the floor and its frame is not required to be braced or made of thicker steel.
You are correct the trailer has drop axles and is running on air bags so it is able to load my race cars without having to raise suspension or using the wooden plank method.
If you look inside you can see the framed triangulation which give the enclosed structure the strength

Wow. Very nice and clever indeed. Must be very stiff. Is there a pair of tubes at the back of the trailer that is at a different angle in the real trailer VS the cad drawing? Was there any FEA done? Are there more pictures you could share?

Thanks
404

 

[theoldwizard1]

I made this trailer and it weights about 700kgs. It is built for a specific purpose, my race car so this design might suit your purpose.

So how do you make it squat ?

 

[alwaysFlOoReD]

the trailer has drop axles and is running on air bags

Richard

 

[Don-F]

I was looking at some of the information here, the diamond plate I used on my old trailer is heavy and I was possibly looking for alternative flooring. All the expanded metal floors I have seen on used trailers had big dips and bends in them. I found a trailer company in another country that uses tube. I like the idea. A 1" x 3/16" (25mm x 3mm) tube spaced 6" (150mm) will weigh about half of the same area diamond plate if my math is correct. My question is why they would bore though the main frame rails to install it, They do seem to be using the tubes as tie down points so maybe its reason is structural. The tube would not be using only the weld to stay in position.
Self built trailers are inspected by the state to be registered in my area, so its best not to do anything too different or be prepared to pay an engineer sign off on it.

 

[404]

May be built by a company that also does ladders..

 

[tpwalsh]

What kind of load do you anticipate with this trailer? Are we talking 1200lb first gen civics? or "lightweight" modern mini coopers?

Here's one that an aquaintence built. Car weighs under 2000lbs and trailer weighs 750lbs.

 

[kerrynzl]

I was looking at some of the information here, the diamond plate I used on my old trailer is heavy and I was possibly looking for alternative flooring. All the expanded metal floors I have seen on used trailers had big dips and bends in them. I found a trailer company in another country that uses tube. I like the idea. A 1" x 3/16" (25mm x 3mm) tube spaced 6" (150mm) will weigh about half of the same area diamond plate if my math is correct. My question is why they would bore though the main frame rails to install it, They do seem to be using the tubes as tie down points so maybe its reason is structural. The tube would not be using only the weld to stay in position.
Self built trailers are inspected by the state to be registered in my area, so its best not to do anything too different or be prepared to pay an engineer sign off on it.

I also found a few pictures of air bag conversions on trailers

Tube decks [and upside down angle] were very popular with the off-road crowd for a while. Probably because the mud falls through.

The weight saving is minimal. A 25mm diameter tube has 78mm of area.
The real problem is the weight bearing load is on one tube if it sits on top , or 2 tubes if it sits between.

And you still need 4 x main rails to support them.

A sheet deck will dissipate the footprint of a tyre over a greater area.

You would be better off buying 1 x sheet of 5mm treadplate aluminium and guillotine it into 3 x 400mm wide strips ,and the 1/2 the third strip.
This will make two 3600mm x 400mm runners.

Then Glue the runners on top of the rails with urethane adhesive.
If you did this you could make the trailer frame from galv tubing which is cheap [then zinc paint the welds]


I think I might build the trailer I described above [maybe bigger]and I’ll post a few photos of the build.


Have a good look at that “Hack Job” airbag conversion and see if you can tell me what is wrong with it.
[on a uneven road it will start to develop stress cracks ] ....... Why?

 

[Don-F]

I think I might build the trailer I described above [maybe bigger]and I’ll post a few photos of the build.

I liked your original trailer build. I would be interested in the other project you have planed.

Have a good look at that “Hack Job” airbag conversion and see if you can tell me what is wrong with it.
[on a uneven road it will start to develop stress cracks ] ....... Why?

I just posted a picture I found, I didn't want airbags on my project. I looked at it and it needs the air bag brackets redesigned to take out the flex on the bottom.

I am not building anything for a while so there is plenty of time to hash out the ideas. Thanks to all who posted.

 

[404]

Have a good look at that “Hack Job” airbag conversion and see if you can tell me what is wrong with it.
[on a uneven road it will start to develop stress cracks ] ....... Why?

For a start because the offset wheel load is only supported by twist of that fragile flower of a pivot bracket? Plenty to pick at on this design.

Or were you thinking of some other defect..

Regards,
404

 

[kerrynzl]

Have a good look at that “Hack Job” airbag conversion and see if you can tell me what is wrong with it.
[on a uneven road it will start to develop stress cracks ] ....... Why?

For a start because the offset wheel load is only supported by twist of that fragile flower of a pivot bracket? Plenty to pick at on this design.

Or were you thinking of some other defect..

Regards,
404

I am referring to the suspension design.

Underneath you can see “U” bolts going through the bottom plate ,so I can assume that it is a beam axle [either straight or dropped]

You never mount a “2-link” suspension to a tube beam axle. [ if this axle had poor torsional resistance it would be OK ish]
By mounting parallel 2 links to the axle it has created a very stiff anti-roll bar through the beam.

This works OK if the owner just wants to show off his bagged suspension, but as soon as it is driven on an uneven surface it will develop cracks in the welds.

Imagine the twisting when trying to drive 1 wheel up a curb.[ that is lateral twisting in the axle,and longitudinal twisting in both links ]

To successfully use a 2 link suspension the front pivots need to be moved together like an “A” frame.
Truck arms are a similar 2-link with the front pivots just each side of the driveshaft ,but they still use a stamped “U”channel for the arms.

 

[404]

I am referring to the suspension design.

Underneath you can see “U” bolts going through the bottom plate ,so I can assume that it is a beam axle [either straight or dropped]

You never mount a “2-link” suspension to a tube beam axle. [ if this axle had poor torsional resistance it would be OK ish]
By mounting parallel 2 links to the axle it has created a very stiff anti-roll bar through the beam.

This works OK if the owner just wants to show off his bagged suspension, but as soon as it is driven on an uneven surface it will develop cracks in the welds.

Imagine the twisting when trying to drive 1 wheel up a curb.[ that is lateral twisting in the axle,and longitudinal twisting in both links ]

To successfully use a 2 link suspension the front pivots need to be moved together like an “A” frame.
Truck arms are a similar 2-link with the front pivots just each side of the driveshaft ,but they still use a stamped “U”channel for the arms.

That is a good catch. Thanks for the info, it is obvious once you mention it but I did not even think of it.

 

[David Walter]

You never mount a “2-link” suspension to a tube beam axle. [ if this axle had poor torsional resistance it would be OK ish]
By mounting parallel 2 links to the axle it has created a very stiff anti-roll bar through the beam.

This works OK if the owner just wants to show off his bagged suspension, but as soon as it is driven on an uneven surface it will develop cracks in the welds.

Imagine the twisting when trying to drive 1 wheel up a curb.[ that is lateral twisting in the axle,and longitudinal twisting in both links ]
.

I actually did change to the beam axle on my trailer from a completely independent setup to have a stabiliser. I found that while the air bags could be adjusted to give the perfect spring pressure the trailer swayed heavily. I was concerned about cracking, so I installed a nylon bushes in the fulcrum, and watched it carefully. I have done some 20,000km plus on the 4x4 tracks we call country highway and roads here in Australia, without issue. And it stays as level as they come.
So don't be concerned about doing the beam axle just be conscious of where the stresses are concentrating, and use these to you advantage.

 

[kerrynzl]

I actually did change to the beam axle on my trailer from a completely independent setup to have a stabiliser. I found that while the air bags could be adjusted to give the perfect spring pressure the trailer swayed heavily. I was concerned about cracking, so I installed a nylon bushes in the fulcrum, and watched it carefully. I have done some 20,000km plus on the 4x4 tracks we call country highway and roads here in Australia, without issue. And it stays as level as they come.
So don't be concerned about doing the beam axle just be conscious of where the stresses are concentrating, and use these to you advantage.

“Staying as level as it comes” is the problem.
Each side of the axle should be able to absorb bumps and not go up and down together.

If you had a 24” long link on each side and one side compresses 6” there will be a 14.48° change in the angles of the 2 links.
That angle variation is trying to put torsional twist down the axle.[ Tube axles don’t twist easily ]
There is also a 0.76” change in the wheelbase during the suspension movement [ or Roll steer ]
If the links were mounted 80” apart the same 6” compression will cause a 4.3° twist in the links. That 4.3° can easily be absorbed into front rubber bushings.

6” of travel is extreme, but when you have 2” of travel over undulating bumps for millions of cycles, that’s when stress cracks develop

I’ve seen similar situations with a pair of ladder bars on a street car, some people get away with it but they always handle like a pig.

 

[Don-F]

I found pictures of a small trailer that use to be made in the USA called a travel-light. They were mentioned in a few "light car trailer" threads I found. It was supposedly rated to haul a car under 3000 lbs. I'm not saying the design is safe, the tongue looks scary. The fender design and the small tires for a low deck height interests me though.

 

[Briggs]

Im not seeing any triangulation in any of these trailers. Throw a couple of diagonal braces in the frame and it will strengthen the trailer 10x.

 

[Don-F]

Im not seeing any triangulation in any of these trailers. Throw a couple of diagonal braces in the frame and it will strengthen the trailer 10x.

I think its because of the direction of the stress that's put on a trailer. Vertical Diagonal bracing like a truss uses is done on a few examples here and was already talked about. If your talking about bracing horizontally, I not sure a trailer needs to be 10X stronger in that direction? I did see one trailer with a few horizontal cross braces. Its a small trailer from Brunton. http://img.photobucket.com/albums/v640/snookwheel/terrytrailer2.jpg

 

[kerrynzl]

Im not seeing any triangulation in any of these trailers. Throw a couple of diagonal braces in the frame and it will strengthen the trailer 10x.

In most cases an "A" frame tongue acts as a diagonal brace [in 2 directions]

Very seldom does a simple ladder frame parallelogram itself [this usually happens during construction if the builder can't use a tape measure]

A ladder frame needs good beaming strength mainly lengthways
In most cases the tyre footprint [weight bearing points] is right out by the main rails so you don't need as much beaming strength laterally .
Dumping a pallet of wood down the centre is a different scenario, which is why Machinery trailers are heavier.
Getting good torsional strength is almost impossible with a ladder frame,
A full diamond plate deck will get better torsional strength by adding a bend in it [a Dovetail rear]

With engineering, Shape is more important than size.

 

[kerrynzl]

I think its because of the direction of the stress that's put on a trailer. Vertical Diagonal bracing like a truss uses is done on a few examples here and was already talked about. http://img.photobucket.com/albums/v640/snookwheel/terrytrailer2.jpg

Those vertical diagonal braces can be eliminated with properly designed fender backs.
The vertical "blade" in the fender back increases the beaming strength at the critical point [over the wheels]
Then the fender itself acts like a stiffener for the backs.
Glue the fenders on, it is a shitload stronger.

If the Tongue is "A" frame shaped and mounted UNDER the frame, you have effectively increased the beaming strength of the front half of the trailer [think of 2 pieces of steel stitch welded to make a higher beam]

The weakest point is usually behind the rear fender [if it has backs]

 

[Don-F]

Thank you for all the information. That explains why so many trailer designs from other countries have top rails and fender backs welded on even if they don't brace the area before or after.

 

[Don-F]

Just an update. I was able to source some plans from Marshall Engineering in Australia. Their plans are more like a book! The trailer is listed at about 400lbs lighter than any steel car trailer made locally that I could find for sale. Most were even more weight at about 1800 lbs (so this design saves about 700 over them). Its not rated as high weight wise, but its plenty for the cars that I own. I will start on the project once the weather gets a bit better here. http://www.marshall-eng.com.au/Car_Carrier.html

 

[kerrynzl]

Just an update. I was able to source some plans from Marshall Engineering in Australia. Their plans are more like a book! The trailer is listed at about 400lbs lighter than any steel car trailer made locally that I could find for sale. Most were even more weight at about 1800 lbs (so this design saves about 700 over them). Its not rated as high weight wise, but its plenty for the cars that I own. I will start on the project once the weather gets a bit better here. http://www.marshall-eng.com.au/Car_Carrier.html

I had a look at the specs on that kitset they're selling. You should be able to pull 50-80 kg from that trailer with a few alterations.
It doesn't need 7 x 50x50 cross bars when 4 x 65x35 standing vertical will have better beaming strength.
The tongue only needs to be 3mm wall [not 5mm in the specs]

 

[Don-F]

Thanks for the tips! I was planing on using a few more hints I have learned from this thread too.

 

[kerrynzl]

Thanks for the tips! I was planing on using a few more hints I have learned from this thread too.

Don [ Foreman ? ]

If you can hang in there for about 4 weeks, I'm going to do a build thread on what you are wanting.

I'm planning in a 4.25m long x 2.02m Wide deck. Tandem with electric brakes.

Target weight will be 450-460 kgs [1000 lbs] yet it will be strong enough to haul a 2200kg [4800 lbs] vehicle

The idea is to put 14-1500kg racecar on it and keep it around 2000kg GVW.
Perfect for club racers.

I already have the steel ordered

 

[toofart]

^^ I'll be watching for that thread.

 

[Don-F]

Yes, thanks! I am not planning on starting a trailer for a few more months because of weather. The garage is full and I have to build the trailer in the driveway.

 

[sberry]

You ought to see the first trailer I built, what a monster. I still might steal some parts but want to use a section of mobile home frame incorporated in to the fender back brace.

 

[BillC6]

Great thread. Attached are photos and a brochure of a trailer that is no longer available but had a good light weight structural design. I used one and the low bed was great compared to leaf spring trailers.