A bicycle trailer
is a motorless wheeled frame with a hitch system designed for transporting cargo
. A bicycle trailer expands the cargo-carrying capacity of a bicycle greatly, allowing point-to-point transport of objects up to 4 cubic yards (3 cubic meters) in volume and weighing as much as half a ton 1
Different types of trailers are adapted to different purposes, cargo requirements, and riding conditions.
By number of wheels
- Single-wheel: a single rear-mounted wheel. Though of limited towing capacity, this design tends to be more stable than trailers with two or more wheels. The single wheel can tilt from side to side when cornering (as the bicycle itself does,) allowing for coordinated turns at relatively high speed. The Bob series of trailers all have a single wheel; comments on using such trailers may be found here
- Two-wheel: A two-wheel design makes possible much greater load carrying capacity and a wider cargo bed, but has a tendency to tip over when making very sharp or high-speed turns. Also, two-wheel trailers tend to be as wide or wider than the handlebars of the bicycle, increasing the risk of hitting objects (or getting stuck) when riding through narrow spaces.
By intended cargo
- General Cargo: for transporting cargo of all kinds. The load capacity of commercially-available cargo trailers ranges from 30 to 300 pounds (14 to 140 kg), but much larger loads have been transported by custom-built trailers or by multi-trailer "trains" attached to a single bicycle.
- Child passenger (as cargo): constructed to enhance the comfort and safety of one or more small human passengers. These usually have an especially low center of gravity and widely-spaced wheels to reduce likelihood of roll-overs when cornering, and often have integrated rain-proof covers, seat padding, and safety belts.
- Child passenger (as rider): Trailer bikes, one-wheel trailers with integrated seat, handle bars, and drive train. These allow small children who can't yet ride a bicycle alone to accompany adult riders as participants and motive-power producers.
- Canoe and Kayak: designed for towing long, thin, relatively light-weight loads such as canoes, kayaks, or wind surfing rigs. For example, see: Kayak trailer
- Disabled passenger: made for safely towing wheelchairs with persons in them.
- Pets: for carrying small domestic animals that weigh less than 30 lb (14 kg). Pet trailer
- Metal: usually steel alloy or aluminum tubing, assembled by brazing, welding, or nuts and bolts.
- Wood: seldom seen but sometimes used in make-shift and home-built trailers, fastened with glue, nails, screws, bolts, or a combination thereof. An example is here, another here bamboo and other improvised materials here
Most trailers have a separate axle for each wheel, like those used on a bicycle. These separate axles usually mount directly on the frame using either threaded nuts, or a quick-release mechanism, or some press fit
arrangement. The use of separate axles for two-wheel trailers allows the load carrying area to be between the wheels with its base below the axles, so as to keep the centre of gravity relatively low.
Some trailers support a normal axle on two sides, others mount the wheel off one side with a stub axle (a one sided axle).
- Traditional spoked bicycle wheel in various sizes. Has the advantage of being light, strong, readily available. Pneumatic tires provide some suspension for the load, larger diameters ride smoothly and have much less drag than many other types of wheels.
- Solid metal wheels with solid treads, such as dolly wheels. Extremely durable but rough riding and usually slow due to small diameter.
- If included, the fender helps to protect the cargo and the towing bicycle from road spray and dirt. On heavy-duty trailers, the fender may be designed to be capable of bearing heavy loads.
Single-wheel trailers generally use a special frame hitch which attaches to both sides of the rear axle, and which incorporates a vertical hinge to allow cornering.
Hitches for two-wheel trailers must incorporate some form of universal joint or flexible coupling (e.g. rubber tube), both to allow cornering and to allow the bicycle to lean while the trailer remains upright. Since such couplings must have some slack in order to function at all, there is the possibility of resonance at certain pedalling speeds and trailer loads, especially in higher gears; the effect is that the trailer feels as if it is 'bumping' the bicycle - the simplest remedies are either to slow down or to pedal faster in a lower gear.
Two-wheel trailers which attach to the rear axle or chainstay generally have an angled towbar to help keep the trailer more or less centrally behind the bicycle.
Trailers tend to have less effect on bicycle handling when hitched at the rear axle or chainstay, since this low attachment point doesn't push the bicycle sideways as much as a higher attachment point can.
- Seat-post: Temporary or permanent clamp assembly attaching trailer hitch to the seat post.
- Rear axle: Special attachment points, integral to the rear quick release skewer or bolted on to solid axles, hold dropouts cut into the trailer hitch. (Under patent by the BOB trailer company?)
- Chainstay: Two-piece sandwiching clamp screws tight over left rear triangle, with protruding socket-and-pin receiver.
- Rear cargo or pannier rack: Some improvised hitches attach to the rear cargo rack or pannier frame. Since rear racks are not structural parts of the bicycle they cannot handle much weight or torque loading.
- Improvised: Ropes, bungee cord, chain, cable, etc. Usually not dependable, often dangerous to rider and cargo.