Bicycle Cargo Trailer

Have you ever wanted to take something extra with you when you ride your bike, but didn't know how you could get it on the bike and still be able to ride?  I have, and believe me one of my favorite challenges about bike riding is figuring out how to strap anything from a tennis racket to a load of firewood to a bike.  There is something about that moment when you wrap that bungee cord around your item just right, pull on it until your fingers hurt, and get it to hook on.  You step back and think to yourself "this is rigged but it just might stay on."

In my effort to carry more things with my bike I decided to build a cargo trailer.  It wasn't going to be a typical trailer though, I wanted something that was Heavy Duty, maybe something that could handle most household appliances.  So I got started just like every other good home made bike trailer, with a pair of garbage picked wheels and a set of tires that were given to me for free.

Here is a quick run down of the main features of the trailer:

1. Large 28"x41" deck
2. Mounts with a quick release ball joint to any bike rack
3. 1" square steel tube frame can accommodate up to 700c/29" wheels and tires
4. 100mm drop out spacing to allow for most bicycle front wheels
5. Space for tool box with tools, straps, and bungee cords
6. Adjustable pulling arm to allow mounting to any bike

My main motivation for building this trailer came from the many "bike move" videos and blog posts on this topic.  A bike move is what it sounds like, moving to a new house by only using bikes for transportation and hauling.  This requires cargo bikes, bike trailers and the blank stares of people as you ride past with a massive load of  stuff on your bike.  This video is my favorite bike move video from a group of bike movers in Bozeman.  This is not me or my video, but it is a great example of what can be done with a bike trailer.

       
There is also a great post on the Utility Cycling blog about this bike move, Bike Move!

If you just watched the video your probably wondering, How much can I really tow with a bike?  Well the company www.bikesatwork.com sells cargo bike trailers and has some great references on hauling large items on bikes.  Check out the How much can I haul?  page for a calculator on towing weight.  They state that "...most people can comfortably pull 300 lbs (137 kg) with a typical mountain bike and cargo trailer..."  Also check out these links for bike gearing and moving advice, Hauling Cargo by bike  I have not purchased anything from this company but from the info they give and the pictures of their trailers in action I believe they sell a good product, but its just a little pricey.

So now that you see the potential behind a simple bike trailer, lets go build one!

NOTE: In order to use this bike trailer you must have a bike rack
         

Here is a list of the tools and materials you will need to by this bike trailer.

Tools

1. 4.5" Angle Grinder with cutoff, grinding, and sanding discs
2. Drill Press with vice or C-clamp (not absolutely needed but makes drilling steel MUCH easier)
3. Drill Bits size 1/4", 5/16" and 3/8"
4. 3/8"-16 Tap
5. Center Punch
6. Hammer
7. Welder ( I am currently using the 90amp flux core welder from Harbor Freight ~$100)
8. Welding gloves and helmet 
9. Tape Measure
10. Sharpie

Materials

1. 1" Square tube steel ( I got most of the steel for this trailer from an old BBQ grill and a bench press stand)
2. 2" x 3/16" steel flat bar ~1ft long
3. 1" x 3/16" steel flat bar ~1ft long
4. 3/8"-24 threaded rod ~1.5" long (This is a fine thread size, and could come from an old bike axle, many of which are this thread size, or just cut off the head of a bolt of this size)
5. QTY 2 -  3/8"-24 nuts (might also be able to use bike axle nuts)
6. QTY 4 - 1/4"-20 x 2" long bolts with nuts and washers
7. QTY 2 - 3/8"-16 x 1.5" long bolts with nuts and washers
8. QTY 4 - 5/16"-18 Eye bolts with nuts and washers
9. ~ 28"x41" piece of 3/4" MDF (This is for the deck of the trailer and you can use what ever you want for this)
10. Quick Disconnect Ball Linkage (McMaster part #6058K34)
11. QTY 2 - Bike wheels and tires ( I used 20" wheels, but the frame design allows for larger 700c wheels)

Thats it, aside from the quick disconnect linkage all items can be found a local hardware store, or picked from old bike parts.  If you are going to purchase the steel I would highly recommend finding a local steel supplier, just search the yellow pages.  If that's not an option for you I would recommend speedymetals.com, they have fair prices and reasonable shipping.  

If your lacking some of the tools I mentioned, find a way to get them.  Borrow them from your uncle, check out yard sales or search craigslist.  These tools are pretty common and should be easy to find for cheap.  For the welder, a MIG is going to be best for this project.  It is completely doable with a stick or even a tig welder so just use what ever you have.  If you have not welded before the 90amp flux core welder I'm using will be easy enough to learn with and at roughly $100 its by far the best bang for your buck.  If you don't know how to weld check the Welding Guide and Learning to Weld from Phil B.

The attached pdf has detail drawings for the frame and the pulling arm, both parts are explained in the next few steps.

The dropouts are easy to make from 2"x3/16" flat bar.  First, put a cutoff wheel on your angel grinder.  Cutoff  wheels for this type of grinder are roughly 1/8" thick, if the wheel you have is thicker than that its not a cutoff wheel its a grinding wheel.  Now put on your safety glasses, this is a must because your grinder will be throwing sparks everywhere.  Mark off 3" section of the bar and cut it off.  I found that a good practice for cutting with a grinder like this is to first make a shallow cut right along your line.  This will act like a guide as you make the rest of the cut.  Repeat 3 more times to get four 3" long pieces.

Now get out the ruler and sharpie and mark a point in the middle of each piece 3/4" from the end.  Then grab your hammer and center punch, put the punch on your mark and hit it with the hammer.  Don't Miss!  Next put one of the pieces in your vice and center up the center punch mark with the drill bit in you drill press.  Clamp everything down tight and put a dab of motor oil on the drill bit.  This is not the ideal coolant method but it will save your drill bit from going dull.  Set your drill press to the lowest speed possible, less than 500 rpm if you can.  Then just drill the hole and repeat for the next three parts.

Next make a few marks from the edges of each hole to the edge of part.  Then get out your grinder and cut from the hole to the edge of the plate.  Once your done with all four dropouts you'll be a cutoff wheel master and ready to tackle the rest of the project.

  

The frame is built from 1"x1" square steel tubing.  I up-cycled this material from an old BBQ grill and a bench press stand.  The tubing already had the nice right angle curved bends in it so I'll I had to do was cut and weld it together.  The main box of the frame came from the legs of the bench press, which were butt welded together.  The two outer parts of the frame came from the BBQ grill and were also butt welded together.  The interior parts of the frame where straight sections of tubing and were welded in after finishing the perimeter of the frame.

If you don't have the luxury of steel tubing lying around you can buy tubing from a local steel supplier.  You don't need bends at the corners but they do make the trailer look nice.  If you have straight tubing you could bend it yourself with a Woodward Fab Pipe/Tube Bender   

The pulling arm attaches the trailer to your bicycle rack.  The arm is made from 1"x1" steel tubing and 1"x3/16" steel flat bar .  The pulling arm attaches to the upright tube on the frame with two pinch bolts.  The top pinch bolt goes through the two clamping plates with the 3/8" holes and around the upright tube.  This clamps firming on to the upright tube.  The bottom pinch bolt tightens against the upright tube and uses the tapped hole. This keeps the arm from twisting on the upright tube.  I chose to attach the pulling arm in this way because wanted to be able to adjust the height of the arm in order to keep the trailer platform level.  By moving the arm up and down I can adjust for different bike rack heights, so the trailer can always be level on any bike its attached to.  

I choose to use MDF for the platform of the trailer, but realize now that it might not have been the best choice.  A treated plywood may be a better choice because it can get wet and not fall apart like MDF.  You can use whatever sheet material you may have but something as rigid as 3/4" MDF or plywood would be preferable.  Making this platform is pretty simple.  The dimensions are 28"x41" for my trailer and I cut a piece using a circular saw.  Then I clamped it to the trailer and marked the radius of the corners and cut those out with a jig saw.  Then I clamped it again to the frame and marked the locations of the mounting holes in the frame.  I drilled the holes with a 1/4" bit, for the 1/4" bolts I called for in the parts.  I also wanted to make sure the platform was not obstructed by the heads of the bolts so I marked out a section around the holes and used my router to cut out a pocket.  

You need to have a bike rack to mount and pull this trailer.  The frame design and pulling arm are centered around this type of setup. The trailer is connected to the bike rack with a Quick Disconnect Ball Linkage (McMaster part #6058K34)  This linkage has a ball much like the towing hitch used on cars and trucks but is much smaller.  The other part of the linkage that attaches to the trailer has a spring release so it is very easy to detach the trailer from the bike but but still securely captures the ball when pulling.  To mount this to your bike rack just drill a 3/8" hole in the platform.  I suggest putting the hole in the center of the rack and forward of the rear axle.  Most racks have cross bar underneath the platform, don't drill though this, but put your hole near it for added stiffness.  Also, when drilling the hole don't drill through your tire!  Its probably best to either remove the rack or your rear wheel from your bike when drilling.  Mount the ball to the bike rack with a 3/8"-24 nut and you done. 


  

I made the frame a little longer in the front so that I would have a spot to mount a tool box.  The tool box is secured with a bungee cord.  Here are the items I carry in the tool box:

1. 1/2" and 9/16" wrenches (for the bolts and nuts used on the trailer)
2. Bungee cords of various lengths and styles
3. a set of ratchet straps (for holding the load)
4. roll of tape (always seems to help when securing the load)

Now just hook the trailer to your bike and load it up.  I have found this trailer to be very maneuverable.  I can ride in slow tight circles with the trailer attached and it just spins in place behind me.  It would be very difficult to jack knife yourself with this trailer but I'm not going to say it can't be done.  

The first thing I hauled with the trailer was the grill in the picture.  I rode 7 miles on fairly flat roads with moderate traffic only had one issue.  The garbage picked wheels really needed to be trued because there was a relatively harsh vibration around 12MPH.  This is an easy fix.

If you have been thinking about building a bike trailer, stop thinking and just do it.  You will be surprised at how useful your bike will become.  If you are moving, you should defiantly consider a Bike Move.  The best part about a cargo bike trailer is the looks that you get from people as you ride by.  Everyone assumes that pulling things with a bike is just not possible, or at least impractical, but their minds will be blown when you cruse past.  Have fun, ride safe and wear a helmet.