We are Car-Light but have been driving to get large loads of groceries & cat litter and/or garden supplies. Tried grocery panniers but they are awkward to load on the bike when full and have limited capacity. We decided it was time for a trailer.
High load capacity at a reasonable weight - Low CoG for stability – Fast, easy one-handed hookup - Parkable in a small space - Cost effective. I couldn't find anything commercially available that met those criteria. So I figured it was time to see if these arthritic fingers could still lay down a decent TIG weld. (First few beads were a little lumpy but I guess it's like riding a bike.)
Fabrication isn't a problem for me, but we haven't used a trailer since the original Cannondale Bugger 35 years ago. So, I read everything I could find about them on Bike Forums' Utility Bike section. Lots of interesting homebuilt trailers there. Most are clearly built on a tight budget by someone with limited tools and design & metalworking experience. This is not a criticism – Lack of money, tooling and skills brings imagination to the forefront. So there's some very clever stuff here.
Weight - All the features I wanted added up to 23 lbs but it's mostly flat around here.
Width – 32” for stability. Can't wheel it through most doors, but it's kept in a garage.
Ground clearance – 4” Not a problem so far, but it's best to be mindful of it when towing.
Far too many welds to think about making more to sell.
Chassis is mostly 1-1/4” x 0.049” square mild steel. Mounting the box well below the axles made for lots of extra work. Axles thread into short pieces of 3/4” chrome moly bored and threaded to 14mm x 1mm. These are brazed into the uprights, along with reinforcing washers to spread the load over a large area of the square tube. Zero camber and just enough toe-in to be sure there isn't toe-out.
Wheels are inexpensive BMX units with nice 48h Weinmann Zac30 rims and no-name 14mm axle hubs. Enough of the axle was threaded to allow me to move the cones over and have abt. 2.5” sticking out on one side. Tires are CST Cyclops. Light and fat enough to roll easily @ 35 PSI.
Finish is Rustoleum “Hammered” silver. Reasonably tough, fast drying and hard to screw up.
Box is from Home Depot and cost about $16. Forget what it's called.
It's impossible to make a clean intersection of two same size square tubes at a compound angle. So I brazed the chassis and the tongue to a piece of 1-1/4” round. When not on it's tail or hooked to the bike, the trailer rests on the front of this tube. So I reinforced the bottom with a thick, short section of 316 stainless tube.
Rearward extensions are lightweight 1-1/4” x 5/8” x 0.035” chrome moly and do not support the load. But combined with small rubber bumpers on the back of the box they support the trailer when parked on it's tail, with the tires off the floor.
The ball is attached to the bike with a mount carved from 1/4” aluminum structural angle. After removing a 6mm axle spacer, (got lucky there) the mount is securely clamped between the left dropout and locknut. Slotted to match the vertical dropout, it does not interfere with wheel removal. When the wheel is off, it is held in place with a 6mm bolt through the rack eyelet. I'll eventually make a “Clamp on the rear stays” mount for a ball in case I ever need to tow it with another bike.
Hitch is a modified QR ball joint. The added tabs allow quick, one handed attachment to the bike. The body pivots on a piece of 1/2” threaded rod. Ball and hitch have been modified to double the up/down range of motion. 316 stainless hoop is for locking, hanging and maneuvering.
I needed to be able to fold the flag when the trailer is parked on it's tail. So I needed a pivot with a controllable amount of friction. Flag is riveted to a piece of aluminum plate that is sandwiched between a piece of stainless that is welded to the left upright and another piece of aluminum plate. The piece of aluminum adjacent to the spring is not attached to the frame but can't pivot around the bolt due to it's shape.
Maiden voyage was a revelation. 4 very full bags of groceries and 20 pounds of cat litter had no effect on handling and was only noticeable when climbing. Tow bike is a homebrewed 69'er based on a very light '85 Trek 850 with a damaged headtube. (Excess cable length is because I need to flip the bars and raise the stem another 3 inches when my Polymyalgia Rheumatica kicks in.)