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How to Build a Car Trailer

Updated on April 27, 2015

Car trailers purchased from a dealer can be very expensive. Meanwhile, a homemade car trailer can be constructed for just a few hundred dollars from parts you can get at a junkyard and an auto parts store. Car trailers are commonly used by racers who need to get their not-so-street-legal race car to the track. They are also popular with people who need to transport nice vehicles but don't want to put mileage on them.

Choosing a Car Trailer Design

A car trailer should be at least 16 feet long to accommodate most cars and small trucks. It is advisable to have a fold down ramp to get the vehicle on and off with ease. Car trailers can be made with a covered base or with wheel runners. The advantage of a covered base is that it can be used to haul other cargo as well as vehicles. The advantage of wheel runners is that you can check under the vehicle and do repairs while it is on the car trailer.

16′ 7K Car Trailer
16′ 7K Car Trailer | Source

Car Trailer Axles

A car trailer can be made with one axle or two. Two axles offer twice as much support and shock absorption. When possible, always choose two axles. Go to a junkyard and look for a pair of heavy duty truck axles. Mobile home axles work especially well since they are designed to support a lot of weight and provide a smooth ride. Look for axles with springs and brakes. Before you take any axles home, check with your state DMV to find out if it is legal to convert them for a car trailer. The width of the car trailer should be about 100 inches. Mobile home axles are wider than this, so cut out the middle section of the axles and weld them back together at the desired width while making sure to line up the spring pads.

Car Trailer Wheels

If the axles you found do not have tires and wheels attached, you must buy them separately. Since you will be hauling a heavy load on the car trailer, it is better to buy them new. You don't want a double blow out at highway speed while towing a prized vehicle. Buy only bias ply nylon tires made specifically for trailers. These come in 14 1/2 inch and 15 inch sizes. Don't forget the spare tire.

Car Trailer Frame

Weld together a rectangle shaped car trailer frame out of 4 by 4 inch steel. The short sides should measure 6 feet 6 inches. The long sides should measure 16 feet. Check your angles and cross measurements to make sure the frame is exactly rectangular. Cut five 6 feet 6 inch cross bars. Weld them inside the rectangular frame. The middle one should be between the two axles which will be a foot and a half past the center. Weld another halfway to the back of the frame. Weld two more beneath the spring hanger mounting points. The last one is welded half way between there and the front of the frame.

Car Trailer Hitch

Cut a piece of 4 by 4 inch steel to 82 inches. Now cut it in half lengthwise to get two identical pieces. These will form the tongue at the front of the car trailer to hold the hitch. Weld them to the bottom of the frame at the front angling toward each other to form the top two sides of a triangle. Cut the tips so they meet at the top and weld. Position the tongue so that the lower tips touch the long sides of the frame and weld them on. Half of the tongue should extend past the front of the frame and half should be below it. Attach a car trailer hitch that matches your towing vehicle at the front of the tongue. Make sure the angle of the tongue works with your hitch. If it doesn't, make adjustments.

Attaching the Axles

Lay the axles on the underside of the car trailer frame. Position them where they will be on both sides of the crossbar that is a foot and a half back of center. Make sure that the axles are properly lined up and weld the spring hangers to the frame. Remove the axles and turn the frame over. It will be very heavy so use machinery and get a lot of friends to help you. Be careful not to drop it on anything or anyone. Once the frame is right side up, finish welds on the top side. Attach the axles.

Covering the Frame

Use heavy gauge metal plates or construction grade metal purlings to cover the frame. If you are covering the entire frame, you will need 104 square feet. If you only want runners for the tires, you will need two long strips that are 16 feet long and 16 inches wide. You will need to buy this in segments. Weld the metal to the frame. Since a car will be driving on this metal, it is beneficial if there is some texture to it to provide traction. If you can't buy textured metal, run a blow torch across the top of the metal to create slight lumping for traction. Fenders should also be added to keep rocks from flying up. You can buy fenders at an auto parts store or make them yourself with extra sheet metal.

Car Trailer Ramps

Ramps are needed to get the car on and off the trailer. Cut two lengths of heavy gauge metal plates or construction grade metal purlings that will allow the vehicle to enter and exit the trailer at a gentle angle. Three or four feet long should be adequate. If you would like the ramps to stay attached, add a hinge at the top of each so they fold over. Add chains to keep them in place while the trailer is in motion. Add additional chains to secure the vehicle in place while the trailor is moving.

Tail Lights

You can buy a taillight kit and brake controller at any auto parts store. Mount the tail lights in the legally appropriate place required by your state and run the wires to the front of the car trailer. Make sure the tail light and brake controller plugs are compatible with the plugs on your tow vehicle. Finally, have the car trailor inspected to make sure that it is street legal and safe before attempting to tow a vehicle on it.

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      Pravin 2 years ago

      Hello Maz,I would like to attempt to bob my old CX500. Some thgnis I really want are a drum brake up front, an old Brooks sprung leather saddle and a girder front end. The girder bit is the thing that puts me off as the rumours are that I'll have to sell the wife and the cat to get one. Most other thgnis I can get hold of , but girders that are substantial enough for the weight mean I can't use an old set from a 1940 british bike. I would like a kind of ball park figure for girders of a length to replace the stock items, to come unfinished so I can weld on lugs etc, and wide enough to accept an old Kwaka H1 drum insie a 19 rim. At least with your answer I can make a decision either way. Or is there a cheaper alternative.Cheers,Paul.