I am planning a bike to move heavy things, separate question here, and sixtyfootersdude is doing a cargo trailer that converges to some extent with my goal to move cargo here. I am not sure whether mounting a trailer wheel is the same as mounting a normal tire but bear with it I am trying to organize sixtyfootersdude's question at the same time as solving my own problem, just answer the question in the title thank you.
lantius is almost right IMO.
use a standard bicycle wheel with a thin through axle, supported from both sides. It's possible to make a really simple trailer this way that will carry quite a lot. The disadvantage is that it's wider than a single sided mount for the same track width (how far apart the contact patches are). Small wheels off kids bikes are often available cheaply or free, and will usually carry 50-100kg each for a few hundred km before they fall apart (come fail immediately, but they're free so don't worry about that).
use a single sided wheelchair hub. They are light and designed so the wheels are easily removable, which is handy for a trailer that will be packed away often. But they will not carry much weight (20-40kg each) because bike trailers get used much harder than wheelchairs do. They're also somewhat expensive unless you can find a stock of wrecked wheelchairs.
use a thick axle with single sided support. MTB hubs come in 15mm (Shimano) and 20mm through axle variants, and a 20mm steel bolt the right length is easy to weld onto the side of a trailer and will hold more weight than even a really well built wheel (you could even drill a 10mm hole through it to save weight. But it does need to be supported well as there is a lot of force on it). I have a trailer built that way that regularly takes 120kg or more without complaint. Unfortunately the build page for it is unfinished even though the trailer is ~3 years old. These 20" wheels are expensive($US135 each) because you will not find them second hand but they work. TriSled use those ones on their load bikes rated to over 100kg/wheel.
You will need to use small wheels on a two wheel trailer (or build your own hubs) because the side forces in corners are more than a 26" or bigger wheel can cope with. With a solid build and care when cornering a 24" wheel can work, but a 16" or 20" wheel will just work. If you build your own hubs with 100mm or more between flanges you could use bigger wheels, but you end up with a very wide wheel (you just added 100mm to the width of the trailer without adding to the load space).
Finally, you must look at Richard Guy Briggs' organ trailer. It's a bike trailer that carries a Hammond organ and player.
The wheel is a pretty simple mechanism. You've got two main options:
1) Through-axle. In this case, the trailer has structural pieces on either side of the wheel. For example, this design is seen on the Bob Yak and Ibex and the Haulin' Colin trailers. The main advantage here is that you can use a normal bicycle hub and you have good structural support. The disadvantage is primarily that the wheel well increases the width of two-wheeled trailers.
2) Wheelchair hub. (See: Phil Wood) This is the design used by the Blue Sky Cycle Cart. A wheelchair hub has an axle you bolt down from only one side. This allows for a narrower body on a two-wheeled trailer, but you must design the axle fastening system carefully or risk having precession loosen it up. There is little reason to use this on a single-wheel trailer, unless for compactness when folding or using some kind of mono-suspension.
Both types of hubs can be built up with any rim. Smaller BMX-sized wheels (ERTRO 406mm) have the advantage of taking up less space, light weight, and strength, but the normal disadvantages of smaller wheels when it comes to rolling over obstacles. 24" (520mm) and 26" (559mm) wheels are larger, but you should design your trailer bed to hang below the axle for maximum stability. Larger wheels are typically only suitable for special applications or in an Extrawheel-type design.
I found inspiration here: (source: malolelei aka Rainer Detering on Wikimedia Commons)
Essentially, he took two bike forks and mounted them on an aluminium frame, then inserted two standard bike wheels.
An additional bonus is that the drawbar can be attached to one of the fork shafts—take a tube whose inner diameter is slightly larger than the outer diameter of the shaft, slide it over the shaft and fix it, e.g. by driving two screws through the shaft and the drawbar.
My trailer is slightly different in the following ways:
- I use square tubes for the frame (30×30×2 mm)
- Rather than using the special clamps shown below, I drilled a hole for each fork in the frame and attached the fork with an M6 screw through the existing hole.
- In addition, I added an aluminium connector between the inner dropouts and the frame.
- The trailer was not specifically designed for heavy loads, as I expect loads it carries to be bulky, but fairly light.
The wheels (I used 26″) feel a bit wobbly. If you rock the trailer back and forth, there’s a significant amount of give, both in the attachment of the forks and in the wheels. It didn’t seem to be a problem in the brief road test I did. If you feel that is an issue, consider the following:
- Bicycle wheels are generally not designed for the lateral forces to which a two-wheeled trailer subjects them. For this reason, commercial trailers often come with smaller wheels and/or rims not normally found on bicycles. Someone suggested that wheelchair wheels have much stronger spokes than bicycle wheels, though I don’t know if simply swapping out the spokes is a feasible option (the holes in the hub and rim might not be large enough to take stronger spokes). Wheels from a tricycle or cargo bike might also be better equipped for the kind of forces experienced here.
- Using steel for the connectors between the dropouts and the frame might make the fork attachment more rigid.
- Additionally attaching the fork with a U clamp at the front (similar to what is shown here) might further reduce movement of the fork.