Step 1: Obtain parts and tools
1/2" conduit bender
punch (or nail)
1/8" bit and 3/8"
half round file
oxy-acetylene torch or arc welder
plentiful brass brazing rod
brazing flux. goggles, and gloves
bricks for holding frame
framing square / "L" layout tool
Finding and Buying Parts
You can find a lot of the parts, particularly if you're near a metal dumpster or a building renovation that might be ripping out conduit. Metal shops often have scraps of flat stock that you might be able to take.
Wheels: Go with what you can find. Feel lucky if you have the option of mountain bike wheels over road bike wheels. The dimensions given here are for carts with 26", 27", or 700c wheels. If you use 24" wheels, you can reduce the cart depth by 1", and if you use 20" wheels reduce the dimensions by 3" (spine and ribs dimensions). 700c and 27" wheels work, but ther're less strong, particularly laterally, which is important when you're hauling a load around corners.
Find wheels at bike shops or in the dumpsters out back. I've had good luck asking bike shops for old wheels, and in college metal recycling dumpsters. Make sure you get 2 of the same diameter, with the diameters within 1/2" or so with the tires on. You can get tubes with small punctures behind bike shops.
Another wheel possibility: It's easiest to use 2 front wheels because they will have the same hub spacing. However, you can use a front wheel and a rear wheel if you make one of the wheel wells longer and increase the hub spacing for the rear wheel to 4 3/4", instead of 4". Or measure your wheels exactly. Hardware stores carry the EMT conduit and hardware.
You will save some money if you can find scrap 3/16" by 1" bar, plywood and 3/8" ID tubing. Try metal dumpsters, scrap bins at machine shops and mechanics' garages, etc.
In the store, hardware parts are generally less expensive in the bulk bins than in pre-packaged boxes. I can't find rod end ball joints anywhere accept mail order (I've used McMaster-Carr). The shaft should be 1 1/4" or more, and have threads that are 3/8"-24 or 3/8"-16. (The 24 and 16 refer to threads per inch.) Get a nut to match the threads. The hole through the ball should be 3/8" wide. You can order it from mcmaster.com. It is part 6072K64 for the oil-impregnated bronze race with a chrome plated steel ball and right hand threads. It costs $5.92 without shipping. I think shipping is $3 or $4. You might consider getting a welding respirator ($12) from McMaster-Carr at the same time.
For plywood, ask at a lumber yard if they have scrap wood. Building renovations and construction also generate waste plywood that will work fine.
Using the tools
To use a conduit bender, line up your bend mark with the arrow on the bender. Step on the foot plate, while pushing down and pulling sideways on the handle of the bender. Bend until the bubble level reads level with no force on the handle.
Working with metal in this project is easy, but takes some practice. To cut with a hacksaw, make sure the piece is clamped well and the cut is close to the clamp. Use the full length of the blade, pushing down hard enough to cut but not hard enough to bind the blade. Use steady, even strokes pushing forward. Don't press down hard on the return stroke. Hold both the back and front of the saw.
When using files, the cutting happens on the forward stroke. Pulling back with downward pressure on the file will only dull the file.
To cut with a tube cutter, align the mark with the cutting wheel and tighten the screw just enough to score the metal all the way around the tube. Tighten a little more and continue turning the tool, ensuring that the cut is in the original groove. Continue around the tube. This tool is useful for the conduit, but a hacksaw is more reliable.
To braze with an oxy-acetylene torch, it's a good idea to get a lesson from someone who knows how. Always set the regulator carefully and keep the tanks well secured so they could not fall. Use gloves, #5 shade eye protection, and work on non-combustible surfaces. Keep fire-extinguishing paraphernalia present. Work with good ventilation, especially with galvanized conduit.
To drill into metal, make a starting dent with a punch or nail, and drill a small hole at high speed with a sharp metal bit. To enlarge it, use a lower speed and watch out for the bit catching as it breaks through the material. Always drill into material secured in a vice or by clamps.
General safety: Wear gloves when things are hot, don't wear gloves with spinning tools. Wear safety glasses when there are chips flying (drilling, cutting). Wear long non-synthetic, non-flammable clothes when working with the torch. Wear closed-toe shoes or boots. Don't breathe fumes from cutting, heating, or painting. Have fun and take care of yourself so you can ride your bike and pull your bike cart and tell your friends how great it is to not use a car.
Step 2: Cart Fabrication overview
Get 5 pieces of 1/2" EMT conduit and cut and bend in the following manner:
Full length. Mark and bend at 2", 41", 61", and 100". Overlap the last 2".
Cut at 59". bend 6 1/2" from each end to make a "U" (spine)
Cut at 38 1/2". bend 5 3/4" from each end to make a "U" (rib 1)
Cut at 38 1/2". bend 5 3/4" from each end to make a "U" (rib 2)
Cut at 38 1/2". bend at 3/4" from each end to make a "U" (wheel well 1)
Cut at 38 1/2". bend at 3/4" from each end to make a "U" (wheel well 2)
Cut at 50" and bend a 45 degree bend 10" from end (bottom pulling arm)
Cut at 51", and bend a 45 degree bend 11" from end (top pulling arm)
Cut a 15" piece (arm brace)
Cut a 72" piece. Bend at 26" from each end to make a "U" (handle)
From flat stock: (1" by 3/16" thick): make (4) 1 1/2" long dropouts with a 3/8" slot.
*Miter the ends of the tubes with a file to fit as shown in the assembly diagram.
*Braze the main-frame, ribs, and spine together.
*Make a dropout jig. each set of dropouts is 4" apart, and space the sets at 22 1/2".
*Put the dropouts in the jig and support the jig level from the ground so that the wheel wells rest on the outside dropouts, and the inside dropouts contact the center rib. Braze.
*Braze the two pulling arm pieces together as shown in the assembly diagram.
*Braze the pulling arm to the front and center ribs. Add the arm-brace.
*Drill a hole in the pulling arm at the end, and attach a 2" long 3/8" bolt as shown.
*Make a hitch out of 1" by 3/16" flat stock, 1/4" rod, and a 3/8" ID tube as shown.
*Make an extended wing nut, attach 2 front bicycle wheels to the cart, paint the joints.
*Add a plywood bed made that is 19" by 38" with notches cut for the ribs and spine.
Step 3: Fabrication of the parts: Main frame
*This piece will be the main frame. With all tubes, make all marks before bending.
*Mark at all the following lengths from one end before bending. Make a small star symbol at the starting end to signify start bending from this side. Mark at 2", 41", 61", and 100".
*Make a dotted line at 118". This will be the mark to which the tube overlaps when it is bent into a rectangle. Eventually, the last 2 inches will be cut off, but the tube is bent with the 2 inches to allow adjustment if the bends are uneven.
*Bend 4 bends to make rectangular shape. With each bend, make sure that the previous bend is in the same plane. Line it up by eye, and fix mistakes by hand.
*Holding the two ends of the tube in overlap of 2", measure the width of the frame at the front and back, before the bends. It should be around 22" or 22 1/2". If the front and back are unequal distances, you can cut off more or less than 2" from the end of the tube. Cut approximately 2" off the end of the tube. Bend the frame by hand so that the two mating tubes are in line with each other.
Step 4: Fabrication of the parts: Spine and one Rib
*Cut a piece 59" long, which will be the spine. Cut a piece 38 1/2" long, which will be one of the two ribs.
*Mark the spine at 6 1/2" from each end.
*Bend from each end to create a wide "U" shape, as shown.
*Mark the rib at 5 3/4" from each end.
*Bend from each end to make another "U" shape, as shown.
Step 5: Fabrication of the parts: One rib and two wheel weels
*Cut another piece 38 1/2" long, which will be the second rib. Mark and bend this rib like the first.
*Cut two pieces 38 1/2" long, which will be the two wheel wells.
***NOTE: If you are going to be using rear wheels for the cart, and don't want to take out the spacers (with hub adjustment), you should add 1 inch to the length of the wheel wells, and cut at 39 1/2" If you don't add length, but use the wider rear hubs, the wheel wells will have less of a slope downward and will be a little weaker. (To visualize this, think about the wheel wells as a part of a structural triangle, from the back of the bike cart looking forward.) You can use any combination of front and rear wheels as long as the diameters are within 1/2".
*Mark the wheel wells at 3/4" from each end. Bend into "U"shapes, as shown.
***Note again. If you added an inch to the wheel wells above, mark the wheel wells 1 1/4" from each end.
Step 6: Fabrication of the parts: Pulling arm
*Cut a piece 50" long. This will be the bottom arm. Mark and bend a 45-degree bend at 10" from one end.
*Cut a piece 51" long. This will be the top arm. Mark and bend a 45-degree bend at 11" from one end.
*Cut a piece 15" long. This will be the arm brace, and will be cut down more once the arm is on the cart.
Step 7: Fabrication of the parts: Handle and third rib
If you don't want a handle, you can save some time and money by skipping the fifth piece which makes an optional third rib and the handle. The handle adds quite a bit of versatility and usability to the cart.
*Cut a third rib that is 38 1/2" long. This is a nice piece for easy attachment of the bed, but is not necessary structurally. Bend at 5 3/4" from each end. Position it where it fits at the back of the cart, mitered where it connects to the main frame and in contact with the spine.
*Cut a piece 72" long. This will be the handle. Mark and bend the handle 26" from each end into a "U" shape. Make sure that the angles are 90 degrees at each bend, or the cart will have a visibly crooked handle.
Step 8: Fabrication of the parts: Wheel Dropouts
*Cut four pieces 1 1/2" long.
*With a nail or a punch and hammer, make a small dent in the middle of the material (3/4" and 1/2" from the edges). Put the piece in a vice, or clamp it really well. Drill a 1/8" pilot hole, and then enlarge to 3/8".
*Using a hacksaw, cut in from the end to meet the hole. The slot should be 3/8" wide. Make sure your wheel axles fit in the slots. Finish the slot with a file.
*File off the sharp edges.
*Repeat, to make a total of 4 dropouts.
Step 9: Miter the tubes to fit together for brazing/welding
Note: make sure the miters go the right direction and are in parallel or perpendicular planes to the rest of the tube. Each miter should only take about a minute. If it takes longer, use stronger strokes (pushing forward only). To determine which direction to miter, refer to the image of the assembled cart, or below.
*Miter the wheel wells, cutting parallel to the bottom of the "U".
*Miter the ribs cutting perpendicular to the tube (opposite from wheel wells).
*Miter the ends of the spine, cutting perpendicular to the tube.
*Miter one end of the arm brace. The other end will be cut straight at an angle later.
*Miter the handle, cutting parallel to the bottom of the "U".
Step 10: Aligning the frame for brazing/welding
*Place the main frame on a flat fire-proof surface. Paint flux on the ends of the tubes and inside of the coupling, and slip the two tubes inside the coupling as far as they will go, ensuring that there is flux at the edge of the joint. If the tubes spring back out, bend them in.
*Measure 19" from the back end of the main frame. Use a square to get even measures on each side of the frame. Mark on the side of the tube, so the mark is visible when a tube is placed on top.
*Place one of the ribs between the two marks. Check to see if the miters fit well. If the tube does not fit, bend by hand until it does. Support this rib with bricks, magnets, or other metal scraps, but not right in the center, where the spine will be.
*Mark for the front rib 16 1/2" in front of the marks for the center rib. This positioning is not exact, but should be right where the bends start on the main frame. The front rib needs to stay out of the way of the wheel well. Adjust to fit, and support this rib as well. Do the same for the back rib.
*Mark the center of the front and back ends of the main frame by marking half-way points on the table where the sides are parallel, then by drawing a line through those points to the main frame end pieces. Lay the spine over the ribs.
*Once the pieces are centered, vertical, aligned, plumb, flush, or otherwise how you want them to be, take them all off and coat each surface that will be brazed with flux. Replace all the pieces.
*Read the brazing information on the following pages. Braze the frame together, starting with the ribs. If the spine does not sit perfectly on the ribs, tilt the ribs towards the curve of the spine until there is contact, or bend the spine down to make contact.
Creating the dropout jig
Note: These measurements assume that you are using 2 front wheels from bikes, with 4" distance between the outside surfaces of the locknuts. If you are using rear hubs or hubs with a different spacing make an appropriate adjustment in the jig.
*If you are lucky enough to find 20" wheels, measure the axle width, adjust the dropout jig, make the wheel wells shorter by 6 inches or so, and take off 3 inches off of each side of the ribs and spine to keep the same clearance. (Axle height on a 26" wheel is 13", and on a 20" wheel it's 10".) If your wheels are strong, the cart with 20" wheels should be more stable and stronger than a cart with larger wheels. Move the wheel wells and center rib back by 6 inches to stabilize the cart. If you are going to be making several trailers, I suggest using nylon nuts for this jig. If you are making just one trailer, you could make a cheaper jig from wood or metal rod. As an alternative to nylon nuts, use 2 regular nuts tightened together.
*Measure the width of the center rib from the outside of the one mitered end to the outside of the other end. Center to center will be about 22, and outside to outside will be about 22 3/4". Take your measurement, and subtract 1/4" (to allow the dropouts to sit well against the tube). It will be about 22 1/2".
*Thread on a wing nut on each side, with the flat side of the nut facing out. Slide on two 3/8" washers on each side.
*Thread 2 nylon nuts onto the threaded rod, one from each end. (The side without the nylon has to go on first.) To hold the rod while threading, you can thread two regular nuts onto the opposite end of the rod and tighten them together. Hold this end in a vice or another wrench.
*Thread the first nylon nut 6" onto the end of the rod. Thread the other nylon nut on the other far enough so the distance from the outside of the two washers is the same as the distance measured along the center rib, minus 1/4" (see above, probably 22 1/2" or so).
*Thread another nylon nut onto each side, so that the distance between the two nylon nuts and two of the washers is the same as the spacing for your wheels. For 26" mountain bike wheels, this distance is 4". For road bike wheels, the distance may be less, down to 3 7/8". If you're using rear wheels, it might be 4 3/4" or more.
*Slide on two more washers on each side. Thread on one more wing nut.
Adding wheel wells and dropouts
*Turn the frame right side up. It will rest on just the spine. Place 4 bricks under the front and back ribs to make the main frame parallel to the ground.
*Place a dropout between each set of washers on the dropout jig(4 sets). Align them on a flat surface with all the slots in the same direction. Tighten the wing nuts.
*Use 4 rubber bands or string to get the wheel wells snug against the main frame.
*Find and mark the centers of the wheel wells (about 16" from each side).
*Place the dropout jig with dropouts on bricks/metal scraps, etc, just behind the center rib. It should be at such a height so that when the wheel wells come down to rest on the outside dropouts, the inside edge of the tube rests
with the dropouts. Note: if the dropouts are centered on the tubes, or too far from the wheel-side of the tube, there could be clearance issues with the spokes hitting the tubes, especially on 700c and 27" wheels. See diagrams.
*When everything is aligned nicely, apply flux, and braze the wheel wells onto the main frame.
*Make a small tack braze on each dropout. Remove the jig before brazing the dropouts completely, or the nylon in the washers will melt or the nuts could get brazed to the dropouts. Brazing the dropouts to the rib will require much more heat than brazing two tubes together because of the wall thickness. To keep from burning through the tubes, aim the flame mostly at the dropout.each side, so that the flat sides of the nuts are facing the washers.
Step 11: Safety considerations
Danger of welding galvanized metal (from cutting, welding, and brazing) You are heating galvanized metal, which is coated in zinc. The zinc will burn off and oxidize in the air, creating zinc oxide. Breathing zinc oxide can cause Metal Fume Fever. According to the American Welding Society, Metal Fume Fever causes flu-like symptoms including headache, fever, chills, muscle aches, thirst, nausea, vomiting, chest soreness, fatigue, gastrointestinal pain, weakness, and tiredness. Symptoms start several hours after exposure and last 6 to 24 hours. The American Welding Society claims that there are no known long-term affects from Metal Fume Fever.
*Braze outside. Portability is one nice thing about oxy-acetylene torches.
*Keep air moving across the work, with a fan or align yourself with wind so that the smoke blows sideways. (If your back is to the wind, your body will stop the airflow in front of your face.)
*Don't breathe the smoke plume.
*Keep your head back from and never above the area that you are brazing.
*Watch the ends of tubes, because fumes will escape from them.
In the process of designing and learning to build bike trailers with galvanized conduit, I got metal fume fever twice, through carelessness. You should be careful, and I think it is possible to braze EMT conduit safely. The sickness felt like the head and body ache that are symptoms of influenza. I felt dehydrated and tired. I felt fine the next morning.
If you cannot ensure adequate ventilation, wear an N95 (or higher) type respirator. You can buy a N99 filter respirator from McMaster-Carr for $11.09 (Part #53565T2). The instructions say it;s good for 8 hours of breathing through, or until it gets hard to breathe through. 2 replacement filters are $5.61. I don;t like buying from large mail-order corporations, but if the tradeoff is getting sick or not building a bike cart, I will do it.
Use #5 shade eye protection. If you look at the flame for a second, you;re not going to lose your sight, but it;s bright and bad for your eyes, a bit worst than looking at the sun. I've heard that you're eyes are safe 10 feet back from the flame.
Use gloves to touch the metal that you are working on. The brazing rod will get hot close to the end.
Metal Fume Fever Information
According to the American Welding Society, Metal Fume Fever is an illness caused by exposure to zinc oxide, a chemical present in fumes from welding and brazing galvanized metal. The symptoms of metal fume fever are flu-like, including headache, nausea, fever, fatigue, and chills. Symptoms start several hours after exposure and last 6 to 24 hours, although total recovery might not be for 48 hours. High levels of exposure may cause metallic taste in mouth, dry and irritated throat, and coughing. Several hours after exposure, you may have a fever (lower than 102 degrees F, then chills before returning to normal). The OSHA standard for zinc oxide exposure is 5 miligrams per cubic meter of air averaged over an 8 hour work shift. NIOSH uses the same 5 mg per m3 (cubic meter), but suggests that it is permissible for 10 hours per day, or 40 hours per week. They further permit a STEL (short term exposure limit) of 10 mg/m3 averaged over a 15 minute period. There is no published information about long term effects of zinc oxide exposure. (American Welding Society. Safety and Health Fact Sheet No. 25) Even though there are no known long term effects, it doesn't make sense to expose yourself to zinc oxide and potentially suffer from Metal Fume Fever, because it's easy to prevent exposure. Brazing, as opposed to welding, produces fewer fumes because of the lower temperatures.
Step 12: Creating the pulling arm
*Coat 2" sections of the tubes with flux at 8" intervals (or so) and braze the tubes together. Make it strong enough to be stiff but not overkill. Braze on both sides of the tubes.
*Let arm cool or dip in water. Place the cart on a flat surface with blocks under the ribs to keep them parallel to the ground. (The same position for brazing the wheel wells and dropouts.)
*Support the arm with three piles of bricks/scrap metal so that the top of it is 1" below the bottom of the dropout on the center rib. This should be about 4 1/2" down from the main frame tube. If you are not using 26", 700c, or 27" wheels for the trailer, or if you are not going to make the trailer for a bike with a rear wheel of those sizes, you will want to adjust this dimension. The goal is to have this arm be parallel to the ground and meet the bike 2 inches under the rear axle. The bottom of the trailer should be at least 4" above the ground.
*Flux and braze the arm to the front and center ribs at the same height. This braze needs to be very strong.
*Measure the distance from the point just before the bend in the arm to the front of the spine at the same height. Cut the arm brace to fit here, ensuring that it intersects the arm at least 14 inches from the hole in the arm, and that the angled cut is aligned so that the mitered side fits the spine, and the angle has a decent fit with the arm. Again, accuracy is not that crucial. It just needs to be strong.
Step 13: Hitch creation
*Start with a piece of the 1" X 3/16" flat stock that you used for the dropout jigs. This will be the hitch plate.
*Cut a piece 3" long.
*Drill a 3/8" hole for the axle 1/2" from the end and 1/2" from each side.
*From one side of the hitch plate, cut towards the hole so that there are 2 parallel cuts 3/8" apart that meet the hole at the widest part.
*Cut the other end at a 30 degree angle. Make the cut so that the shortest side is the side that has the slot cut into it. Make two more cuts to create a place for the ball joint nut to freely spin, as pictured.
*Clamp the slotted end of the piece in a vice at a 30 degree angle from vertical. Clamp it so that the slot is hidden in the vice by 1/2" and so that the end of the piece is parallel to the ground.
*Look at the hitch plate from the side so that the metal angles upward from the vice to the right. Hit the piece with a hammer away from your point of view to make a bend in the hitch plate away from the bike. The end of the piece should be bent until it is about 1/2" away from vertical. The purpose of this bend is to get the ball joint far enough away from the wheel that there are no clearance issues.
*Get a 3/8" threaded female coupler from a hardware store. It will probably be 1 3/4" long. Holding it firmly in a vice, drill out the threads with a 3/8" drill bit. If you have bits close in size to 3/8", start smaller and increase the dimension. If you don't, be really careful doing this part because the bit can grab the metal and twist the drill forcefully. Cut its length in half with a hacksaw. File smooth. This tube will hold the ball joint loosely so it can turn freely. Alternative: cut a 7/8" long piece of tubing that has a 3/8" ID.
*Place the hitch plate on a flat surface so that the end with the slot is sticking up.
*Line up the tube along the angle of the hitch plate, so that the ball joint sticking out of the end could rotate freely. Make sure that there is enough room for a 3/8" nut (which has a 1/2" head) to spin freely at the end of the tube. This needs to be very strong.
*Cut a piece of 1/4" or 5/16" rod that is 8 inches long. Bend the end in the shape shown in the diagrams (a hook to go around the chainstay).
*Braze the rod onto the opposite side of the hitch plate, so that the straight end runs at the same angle as the cut, making sure that it does not hang over the edge of the cut. See diagram for details.
*Put the hitch on a bike through the left side axle. Loosely tighten the axle nut. With a vice, hammer, pliers, or your hands, bend the rod until it fits well on the chainstay and meets the rest of the hitch. The 3/8" ID tube needs to be parallel to the ground and the hooked arm should rest on the chainstay without interfering with the spokes of the wheel.
*File everything smooth. Paint the hitch. Once dry, attach the rod end ball joint through the tube, and secure it with a nylon lock-nut. Make sure the ball joint can spin freely without play.
Step 14: Finishing the cart
*Crush the end of the pulling arm slightly around the bolt hole so a 3/8" nut just slides inside. Slide a 2" long 3/8" bolt through the arm, from the top to the bottom, threaded through the bolt inside the arm. Slip a 3/8" split-ring lock washer on, and then thread another 3/8" nut onto the end of the bolt and tighten it until the tube is crushed around the interior nut. Thread one more 3/8" nut onto the bolt. Make it tight. Option: Braze the nuts and bolt together, and to the arm.
*Take a 3/8" wing nut and braze a 2" long piece of scrap metal onto the two wings. Use some of the rod from the hitch, or whatever you find. This will be the nut that attaches the cart to the bike, and the wing nut extension allows removal without tools. (Alternative: use a 3/8" nut with a wrench.)
*Attach the wheels to the cart. If there are quick release skewers, put the levers on the outside of the cart.
*Paint the joints of the cart with an outdoor metal paint and/or primer. You don't need spray paint. Any anti-rust brush-on paint works. Paint the hitch too, but not the inside of the nuts (clamp hitch). Remove the ball joint before painting the hitch.
*Add a bed. Use 1/2" plywood that is 19" by 38". Use any kind of clamp to attach the bed to the ribs. Plumbing or conduit clamps work. Sheet metal strips with punched holes are cheaper but more work. You could try plumbers' tape, screwing through the holes into the plywood. Cut slots in the plywood to fit the tubes where they curve. This part can be any kind of creative expression. Metal, driftwood, plastic, canvas, plywood, rope, glass--some ideas are better suited to certain applications.
*Make tie-down straps out of old bicycle tubes, with the valve cut off. Use bowline knots to attach them to the main frame.
*A nice option: Add something unique and special to the cart. My personal favorite is a pole with space for art and signs.
"One less car"
"Yes, I'm moving by bike"
"One less car; make it two?"
Step 15: Possibilities
Step 16: Buying and Selling carts
If you want make these carts to sell, go ahead, but please include a link to the Instructables page or a copy of the fabrication manual from bikecart.pedalpeople.com My goals are to increase car independence and empower people through fabrication in their communities. Let me know if you sell these carts, and what you think about this project. If you build a cart for yourself, let me know how it goes because I'm continuously working on the design and feedback is useful.
One of the more time consuming parts of cart fabrication is finding wheels and tires and making the plywood bed. One way to spread these bike carts might be to build and sell just the cart body, and let the user find and mount wheels and plywood.
If you want to make a bike cart but can't make a hitch, I will send you one for the cost of parts, postage, and the time for making it (cost is $20 in 2006. $6 for the hitch, $2 for metal stock, for $4 for postage, and the rest for time and gas). I want to increase the accessibility of this project. For more information, contact me at firstname.lastname@example.org. These hitches are compatible with Bikes At Work trailers.