Bike Trailer Design and Use
Here I will try to outline the key findings I have discovered in ten years of researching, designing, building, using and repairing bike-trailers. I present my findings and opinions below, in an A-Z list to help you jump to specific bits that might interest you. If you have questions, suggestions or corrections, please let me know – here is an email form on the ABOUT page. This page will probably never be ‘finished’ as I hope to continue adding (and removing) sections as my knowledge grows. Most of these ideas relate to designing and making a D.I.Y. bike trailer while some are more about using a bike-trailer safely.
Aluminium. …is a light and strong metal that does not rust. It is expensive but does sometimes appear in skips / scrap-stores. I have never used it to make a bike-trailer, but that’s only because I have not YET found enough aluminium poles.
Anchors. This is the word I use for places you can hook a bungee into securely. The simplest is a hole in the structure, but beware of weakening your walls / floor. You can buy little metal u-shaped plates that can be screwed to a wooden wall, but they are not that cheap.
Balance. When loading a bike-trailer it’s best to get the centre-of-gravity of the load to lie a little bit in front of the wheels (towards the bike). If you don’t do this, and more of the weight is behind the wheels, you get an annoying and dangerous pendulum effect when turning. So when designing the
Brackets. To make the corners of a wooden trailer strong you need good tight joints (with glue and / or screws or bolts). You could also add brackets into the inside faces of these joints to make them even stronger. But beware of adding too much weight to your structure. Thin steel shelf-brackets are quite light and come ready painted – these can add strengthening to a joint / corner of the trailer.
Bungees. Elasticated ropes with big hooks on the ends are very useful to hold luggage down in your trailer. this means that they won’t bounce out when you hit a bump or take a tight corner. But please note that these are quite dangerous if used in a rush / with wet hands / in the dark. There is a real risk of one coming loose and flicking back to whack you (or a friend) in the face. BEWARE.
Cycle-lane. A trailer will usually make your presence on the road wider. So sometimes you won’t fit between the curb and the cars. I often pull out of the cycle-lane and join the car-lane in slow-moving traffic to allow faster cyclists full access to the cycle-lane, especially at rush hour.
Fenders. If you think that users of your bike-trailer MIGHT carry people (and or kids / dogs) then try to think about making a protective barrier between them and the wheels! If someone’s fingers, or long hair, or scarf gets caught in the spokes of a fast-moving bike-trailer you may have a serious problem! Thin lightweight plywood ‘fenders’ can prevent such dangers, and also they will prevent flappy luggage from drifting towards the spokes. If you are going to be going off-road in wet weather you may also want to add mud-guards.
Flags. If you are using a trailer in an urban area, where lots of parked cars are around, please consider getting a flag attached to the rear road-side end of your trailer. That way, a rushing taxi will know that you are not just a cyclist, and might not smash into your trailer! making a flag can be fun, and it might involve bright colours, a wind-sock, fake-fur, tiny bells, flourescent cloth and the imagination of a young person. I usually make them triangular so even in a mild wind they flutter outwards, and I use tough gaffer-tape to stick them to a bamboo cane. You can make a proper flag-holder out of a bit of plastic piping, attached to the trailer with two strong cable-ties. Or you can use a short bungee, depending on what kind of wall your trailer has – this has the advantage of allowing the flag pole to ‘bend’ down when you go under low branches / fencing / other barricades.
Floors. Thins strong plywood can make a good floor if well supported and kept from rotting. I prefer nets as they are so much lighter, keep bags and boxes snug, are more comfortable when sitting in, and are less noisy. Carrying fragile goods are also more cushioned in netting. Wind and rain sails through. Choose a strong net and inspect it for damage regularly. A net made of a synthetic material can be very strong and won’t rot if allowed to get (and stay) wet.
Glue. I prefer using an expending polyuerothane foam glue. An outdoor PVA is also quite good, especially if the joint is good and tight, and clamped overnight.
Hand-cart. A good bike-trailer can also make a great hand-cart. This is one reason I tend to make trailers that have a ‘neck’ that bring the trailer up to meet the bike near the saddle-post. Sometimes you will be moving goods just a short distance, or with a group of walkers, so having a nice hand-fitting handle at around waist height is a good idea.
Hitch. There are dozens of very complex, expensive and precious hitching mechanisms on the market to safely keep your trailer attached to your bike. If one part is lost / stolen they become useless. I tried making a few joining mechanisms including giant carabiners, rope, u-bolts, etc and none were very good. A temporary fix then evolved to be a great, safe and cheap method: a good strong bungee. See the page ‘The Bungee Hitch’ for a fuller description, photos and tips.
Joints and Joining. If you are using wood to manke the trailer I’d recommend using many little screws AND a good strong wood-glue AND use clamps to helod it all together while the glue sets. I used to use PVA weatherproof wood-glue, but more recently I have ben using an even stronger expanding polyuerathane foam glue. Glue works best on dry clean surfaces that are squeezed together for a few hours (or overnight).
Linseed Oil. …is a good and natural wood-preserving oil that smells quite nice too. You can get boiled and raw, and they are quite similar but the boiled variety apparently dries a bit quicker. It will still take a few days to dry fully. A wooden bike-trailer that is often rained on, and / or stored in a place where it gets a lot of sun, will benefit from being repainted with linseed oil every year. I usually give my trailers a coat every 2-3 years.
Metal. By weight, steel pipe-work is quite a lot stronger than wood but it is harder to find as salvage in good condition. Brand new it is quite expensive. I tend not to use it as I do not do welding. I did make one great trailer (The Play-Frame) using metal pipe-work and bolts. We simply drilled holes through the pipe and used strong stainless steel bolts with lock-nuts to hold it all together. This seemed like a great method, but the places where we had drilled holes left the metal pipes weakened, and more exposed to moisture, and rust.
Mud-guards. I tend not to bother with these on bike-trailers as the wheels tend to be ‘outside’ of the carrying area. But if you are going to use the trailer in wet weather a lot, and off-road, then mud-guards may be a good idea. See also ‘Fenders’ above.
Nets. See Floors above.
One wheel or two. I have always gone for two wheels on my bike trailers as I really like the stability. But I have read strong arguments for trying to use just one. A great example is the FarFarer – a very simple but great looking trailer, especially good for long-distance and off-road use. Having one wheel will almost certainly mean that you need a much more robust hitch mechanism, probably one that does not rotate like a ball-and-socket, but only bends like a door hinge. One reasen to favour one-wheeled trailers is that they can lean into a turn, like your bike does. Another bonnus is that having just one wheel makes them lighter (and maybe cheaper) that trailers with two wheels.
Paint. Protecting metal from rusting is a VERY good idea. I tend to use a nasty oil-based metal-paint (such as Hammerite) for this. I tend to avoid paint on wood. Wood is porous and likes to breathe – painting it with a waterproof layer of gloss-paint might keep some water out for a while, but as soon as you have a crack in at paint, water will get in, and stay in and rot the wood. This is a trap. So instead I use a natural oil like linseed oil to coat my wooden bike-trailers. See Linseed Oil above.
Pets. Some folks want to take dogs (and other pets) in a bike-trailer, maybe in order to take it to a nice big park for a good long run. PLEASE put the animal’s interests first. A large dog that is dying for a run might get quite jumpy if caged in a flimsy wheeled box on a fast-moving busy road. If it decided to try to get out of the trailer while it was rolling, that could tip over the trailer and cause a serious accident. Any trailer that is going to take a pet should really be quite strong, low-to the ground, and include a very comfortable but strong mechanism to keep the animal in the trailer, and low. Please take a quieter route, avoiding main roads as that will make your passenger much less like;ly to panic. And if in doubt, slow down and consider walking on the pavement through busy areas.
Purchased bike-trailers. If you aren’t very poor, the easiest way to get to use a good bike-trailer is to buy one. I describe many factory-made trailers (available in the UK) on the Others’ Bike Trailers page.
Visibility. Be safe! Be seen! Consider extra lights on the back of the trailer, white or flourescent reflectors, a flag, faery lights, bells and cycling in a predictable and confident way so motorists and other cyclists can anticipate your movements.
Weight. The best trailers are not too heavy. That is a good feature of metal pipe-work, especially aluminium. If you live in fairly hilly area, the weight of the trailer will be even more important. If you are working with wood, consider using a frame of narrow beams, maybe 45mm in diameter (2by2s), to make the basic skeleton. If you want solid walls or a floor, consider plywood of between 4 and 6mm. Any thicker is probably not needed and will be a heavier. Using net instead of plywood for the floor
Wheels. I used to think a smaller lighter wheel would be best for a bike-trailer, but I now prefer larger wheels as they are much less likely to jump up when you hit a pot-hole or acurb.
Wood. I tend to use wood to make my trailers, principally because I am more familiar with working in wood. Metal (pipes) is strong for the weight, but requires welding / bolting, and is often prone to rusting. The wooden planks that are used in beds are ideal for making into bike-trailers as they are quite strong, but also light and often well dried. You can often find these in skips, or jumble-sales or going spare via a friend / newspaper advert / scrap-store. Wood that is quite knotty can be quite strong as the grains are tighter and more knotted around a knot. But larger knots can also make that section of wood weaker than a knot-free piece. So be careful which plank you use where. I tend to avoid green woods as hey are wet and prone to warping in time. I also avoid pallet wood as they are often quite fragile being made of fast-growing wood (big gaps between grain-lines) and often have a lot of splinters. If you do use pallet wood watch out for nails and screws! When working with wood, watch out of splinters! I always rasp and sand all edges of a completed trailer to take away all sharp edges and reduce the risk of splinters to users later.