What is the best way to attach two bike wheels on an axle?

buy weels with hubs bored and keyed to the axle size you want. this is done either by buying a bike trailer from retail then chopping it, shopping hard on ebay/amazon, worksman direct, bike shops, etc. read more

Bike wheels (or rather their hubs) are generally completely different to trailer wheels - trailer (or wheelchair, etc.) wheels fix rigidly onto a rotating axle, with external bearings or bushings between axle and vehicle body, while bike wheels rotate around a stationary axle with bearings inside the hub which are designed to have an equal(ish) load on either side. read more

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). read more