How to Make a Bicycle Trailer Cart for a Carseat

Originally I had made an adaptor for my childrens wagon handle to work with a hitch I had made for my bicycle so that I could pull them in the wagon. This worked fine until we rode to the park one day, and my son and I were having too much of a good time. When I got to the bottom of the hill he was laughing his head off careening down there, and I did a quick loop at the bottom of the hill. Well, this sent him sailing out of the wagon. It happened to be a day my ex-wife actually came with to the park, and she came unglued at the thought of him sailing out of the wagon. He was young and bouncy and loved it, but it inspired what I dubbed my trailer cart.

Pontiacs big theme was wider is better, so I adopted it myself and figured if it was good for Pontiac it would work for my sons trailer cart. I didnt model it exactly this way, but the original was literally almost as wide as a city sidewalk- I wasnt fooling around, and didnt want to have to slow down any because of worrying about tipping over. I knew my son would enjoy the quick ride, too, and I even devised a method for him to have a ready-made 5-point harness. He was still in a carseat at the time, which had a harness, so I designed the trailer cart around housing his carseat, which is how this resulted. Wider is better, 5-point harness- got it!

I did not take pictures of the project as this was made years ago, and I may still be able to dig up a finished product picture anyway, but even so it was taken at night, so I have modeled a similar likeness in CAD. It isn't as good as pictures would be and it isn't exact, but it shouldnt be anyway. You will need to modify yours to fit your needs, and you may not want to take up an entire city sidewalk, but remember, the little tikes are safer when you follow the mantra: Wider is Better.

Step 1: Tools Needed

Hammer
Drill (electric, cordless, hand)
Hand or Circular or Chop Radial Arm or equivalent Saw
Screwdriver or equivalent to tighten eyebolts
Adjustable Wrenches or sockets or equivalent

Step 2: Supplies and Beginning Assembly

So working as much as possible with what I had at my disposal, it ended up with what was certainly not the lightest or most efficient product, but one that certainly worked for my son and I (I know it should be me and not I, but whatever- that is a dumb sounding rule). I had some 2x4s, so I decided to make a ladder frame that was going to be very stout, and it used a single leaf spring/axle support combination for the super-wide rear cross beam.

I nailed the ladder frame together, but screws would have been just fine. I guess-timated how many cross supports it would need, but I would go with no less than three. I went for overkill at the time.

The cross beam axle support should be attached in a relatively square relation to the ladder frame, but because this is attached with a swivel, it isn't critical- close enough is good enough.

To accommodate the swivel, what I did at the time was to cut a couple of squares of plywood and drill matching holes through the center of them. I had some scrap countertop laminate, and figured that since laminate slides pretty well on itself when it is finished side to finished side I would laminate the two pieces, connect them with a bolt through the middle and let this act as my pivot. Now, there are many other better methods for a pivot, but I used what I had. I looked at buying a lazy Susan bearing set, or several other things- you can do what you want. Had I put some grease between the pieces of laminate it would have worked even better. I just didnt think of it at the time.

The top piece of the swivel would hard mount to the ladder frame, while the lower half would mount the wheel and swivel.

On the bottom piece of the swivel I screwed two more pieces of 2x4, mounted vertically, to act as the front wheel supports. I spaced them about a 1/4" outside of the wheel width so that there wasn't too much play side to side. I drilled a hole for the wheel axles (a bolt and locknut) to go through. It is probably a good idea to mount one board to the swivel, put the bolt through it and into the wheel, then screw the second 2x4 in after the wheel is lined up for sure.

For the rear wheels I just bought lag screws that fit just inside the wheel opening. I drilled holes in the ends of the cross beam slightly smaller than the minor diameter of the threads (the inner shank of the threaded portion), so that the lag screw would still have material to bite into, but that it would go in as straight as drilled.

Step 3: The Upright and Seat Attachments

The next major piece is the upright- this needs to be firmly attached to the back of the ladder frame and to the cross beam. It just so happened that the carseat I was using had two indentations that a 2x4 could just fit into on the back of, spaced almost perfectly so that I could use a 2x4 upright, nail the 2x4s facing forward to the upright, and they fit into the carseat. This made for a very stable situation as far as the seat not tipping. If you do not have that type of luxury, I suggest finding another way to locate the seat side to side- this needs to be robust, otherwise the safety will not be there. Again, I got lucky on this part that it fit my 2x4s but most carseats are molded plastic in the back anyway and should have some reliefs you can work with.

I set my carseat on the cart, measured vertically to the reliefs in the back, and cut my vertical upright. Then I nailed the two pieces, one on each side of the upright, facing forward to protrude enough into the carseat.

I also added eyehooks to the crossbeam. When I set the seat onto the frame, it fit into the 2x4s of the upright, but I wanted it more secure that just that, so I put an eyebolt on each side and used a ratchet strap to hold the seat down. Between the ratchet strap, the 2x4s and my sons weight on the seat, he didnt go anywhere!

Lastly, I added a comfort item for him. I realized that he didnt really have a great place to put his feet, so I cut a section of dowel out to make a foot bar. I screwed it down to the ladder frame, sticking out off of each side by several inches, just plenty enough for him to fit his shoes on. The easiest way since it is round is to probably drill one hole and screw it down to one side, then with it more secure you can drill the second hole and screw the second one in.

Step 4: Pull Handle

Lastly, you need to add a handle. I had already modified my childrens wagon handle (actually replaced) with a wooden one to actually fit my hand so I could pull them in it. I stole the wagon handle and handlebar and mounted it on the lower portion of the swivel so as to guide the front wheel. You could make the handle one so that you could hand pull your child, but the trailer cart was meant for speed and stability at speed, so I made it fit my bicycle hitch. I do not recall exactly the design of the hitch, but there are plenty of hitch instructables out there.

Be safe, have fun and go fast!!! Your kids will love it- just be ready for them to ask you to go again.