101 How to Build a Bike Trailer

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    How to build a bike trailerand xtra tips

    been meaning to build a bike trailer for, well, eh, about twenty yearsactually. This page documents my various attempts, successes,failures, inspirations and notes from my research in theIve process.Early attempts and failures

    Ive now built several trailers that work and had a couple that did not.!y first failure was my first attempt about twenty years ago. It was asingle wheel trailer inspired by the "ob #ak. It was built using a childsscooter which back then where large and styled like "!$. It failedrepeatedly under load as my welding was crap. Twenty years on, mymark II attempt works but that long awaited success came only after I

    built my first successful two wheel trailer. In between, I startedanother two wheel trailer which was destined to fail. %dditionally,before succeeding with the single wheel trailer, I did a version of itwith a seat post hitch which was a disaster.

    &o what did I learn from these early attempts and failures' (ell, Ilearned more about welding and the limits of what I could expect froman %)* welder. I learned more about balance, stability and whycertain designs are more popular with others.

    !y Twin (heel Trailer

    This was surprisingly +uick and easy to make. It cost nothing to buildbeyond the cost of grinding disks and welding rods. I was given two- "!$ wheels with tubes and tires / a front and a back wheel. Iused 0exion 1or 0exion style2 angle iron to form the axle mounts withan angle grinder to form slots for the axles to sit in. I then weldedmounts on rusty old 345 electric conduit which I used to form thetrailers frame. I hand bent the pipes to shape by inserting it downinside the bumper of my van as some kind of improvised holder. The

    frame was welded together to form one piece including the hitch armwhich was bent up a little as it moved away from the trailer so that itwould meet the hub on the rear wheel of the bike as the arm sweptinwards.

    I had planned to make a flat bed with a wooded base but I couldntfind a piece of suitably si6ed wood and couldnt be arsed to cut

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    anything. Instead I looked around for another option and came upwith a plastic stacking tray 1like a bread tray but with e+ual heightsides all round2. It fitted perfectly into the frame creating a recessedbox with a lovely low centre of gravity. Ideally Id have more than oneof these as they stack either into or on top of each other / veryhandy. The box 7ust lifts out, which is great for transferring thecontents indoors.

    The hardest bit was the hitch. I tried several methods for the mountbut have currently settled on two links of chain, a bit of inner tube andpart of an old fashioned side pull brake caliper. "asically, one end ofthe chain is inserted into the end of the pipe which forms the hitcharm. % hole is drilled and a bolt put through to hold the chainlink inplace. The other link is cut, opened a little and hooked into bolt hold

    on the bit of the caliper then hammered closed. The inner tube isslide over and cable tied in place. It serves two purposes8 making thechain links less noisy when they move, and protecting the paint onthe chain stay where the hitch point touches when fitted. It is fitted byremoving the +uick release axle off the rear wheel of the bike andreplacing it after threading it through the hitch mechanism.

    The only problems I can currently see or predict with the trailer are asfollows. The pipe bending was poorly done and introduced kinks into

    which will have weakened the metal. (ith inconsistent bends and noaccurate measurements anywhere, the frame isnt entirelysymmetrical. This means that the box isnt +uite a perfect fit, it hasabout 9cm play side to side and one corner tends to drop a little. Theshape of the hitch arm is incorrect and reduces the available turningcircle in one direction as the rear wheel sometimes hits the arm. Thearm probably isnt super strong where it meets the rest of the frame /I expect it will snap there if anywhere. :inally, the wheels I used weredifferent widths 1always the case with front and back wheels2 and sothe axle mounts only fit with the wheels on specific sides. In future Id

    either try to use two front wheels 1or two back, although in theory theyare not generally as strong2, or Id add spacers to the axle on thefront wheel so the spacing was the same as the back.

    ;pdate. %s I expected, the hitch arm broke off which gave me achance to reshape it a little before welding it back on. I slipped asmaller diameter tube of metal inside before re

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    stronger and for good measure I also welded a 5 strip of metal onthe underside.

    ;pdate . %fter another few months of use the arm broke off again.Ive not yet fixed it and since I was finding the hitch annoying anyway,I think Ill change the design and switch to a seat post mountedsystem.!y &ingle (heel Trailer

    The single wheel trailer was much harder to build successfully. I didntbuild a frame or flat bed, instead the front and back parts of the trailerwere both welded to short lengths of 0exion angle iron which in turnwere bolted to the front and back of a plastic stacking box previouslyused by Halfords 1very similar to =ickfords removal boxes2.

    :or the back end I used the rear triangle and wheel from a childs bikewith 9> wheels. I cut the triangle up a bit and re

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    eye height. &till to come will be a mud guard and drain holes in thebox as I am sure it will not be rain proof. I might even consider awater proof cover with elasticated edges.

    The trailer is great, I love it. It tracks perfectly behind the bike allowingyou to weave in and out of lamp posts, trees, pedestrians, parkedcars etc without ever clipping them like you would with a two wheeltrailer. )iding in traffic is pretty ama6ing as you can still nip down thegaps you would if you didnt have a trailer. (hen heavily loaded thebike does feel a little strange, different to how the two wheel trailermakes it feel. &topping, loading or unloading is a bit of a pain as youhave to find something to lean the bike and trailer against. &lowspeed close +uarters maneuvering, especially reversing, can be areal pain, especially when you are off the bike and wheeling it. The

    turning circle in this scenario is awful. ?ether

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    to the box. The construction is ultimately very similar to the modifiedrear triangle I used on the first but without the seat post4upright part.This means it is a little lighter but meant I had nowhere to stick theflag pole. I wasnt entirely sure this would be strong enough and Ineeded somewhere to attach a mudguard and flag pole so I weldedon a couple of diagonal braces. These start half way along the forkson the A brake mounting points and then angle in and forward to slotinto the handle area of the box. % hori6ontal piece is welded betweenthe two providing the mount for the mud guard and flag. I havent yetbuild the +uick release and there are subtle differences in the dropoutof the forks I am using which make me concerned.Two wheeled trailer two

    This trailer was built using parts from a failed, non welded trailer built

    using two 9> wheels and two > front forks. The original attemptwas designed to have a very low center of gravity with a flat bed. Thewheel were mounted right at the back which meant about B-C of theweight was placed onto the bike which is not normal for two wheeltrailers. at first I tried a seat post hitch but as soon a weight was puton the trailer the front part would hit the ground. I then tried achainstay hitch which worked much better but if weight was place atthe front on the derailer side of the trailer then that corner would dipdown and hit the ground.

    I scraped the pro7ect when a friend wanted to build a trailer. (e tookit to pieces and started again, this time mounting the wheels morecentrally. The construction used angle iron 1from road signs2 whichwas welded to the forks. The frame flexed and twisted a lot until wegave up with the flat bed idea and built sides and a back to createbracing and protect the wheels from the carried load. The designcriteria called for a trailer narrow enough to go through doors and witha seat post hitch so that it could be used as a hand cart whenneeded. (e used a bent piece of 345 conduit for the hitch arm then

    rubber hose and a piece of rubber cut from the side wall of a car tyrefor the actual hitch.

    %part from the problem with the twist which was solved withadditional bracing, the other main problem was the fact that the forkswhere positioned in such a way that the dropout slots face up andtowards the rear. This increases the likelihood of a wheel popping out

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    which is exactly what happened when we tested it will a person onthe back.Construction ConsiderationsTwo wheel vs One wheel (mono wheel / single wheel)

    &ingle wheel trailers track accurately behind the the bike, butapparently they may end up steering the bike and putting excessstresses on its frame. *arrying more than 3-kg on a monowheeltrailer is not recommended. They are apparently best for off

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    narrower 1great for trail riding or congested streets2 leans with bike 1D less likely to roll over when rounding corners athigh speed2 comparatively low cargo capacity 1both in weight and volume2 must be loaded and unloaded symmetrically to keep trailer fromtipping over some have reported they can wobble when loaded heavily Easier to add suspension ?ot as forgiving of poor design and construction

    Choice of Wheels

    &maller wheels theoretically bounce more and are slower due tohigher rolling resistance but in practice it is probably irrelevant.

    &maller wheels make it easier to build something with a low centre ofgravity and I think they are probably stronger. (heels are either steelor alloy. %lloy is lighter but may not be as strong as steel. )eally its acase of using what you can get your hands on, but ideally Id say thebest bet are - "!$ wheels with loads of spokes. "!$ wheels arevery strong but not as easy to obtain as > mountain bike wheels.Fids bikes can provide good wheels too but check there are actuallybearings as some dont. (heel chair wheels with half axles are alsovery handy but harder to come by than bike wheels.

    &ome possibilities

    G41G--mm2 road4racing bike 1weakest option2 > mountain bike 1very east to obtain2 5 kids mountain bike 1good compromise2 - bmx and kids bikes 1best option for two wheel cargo trailers2 9> from kids bikes 1good, best for single wheel design2

    uide to Fids "ike &i6es%ge *hilds Height "ike (heel &i6e

    / B > / 35 inches 9 inches5 / 35 / 5 inches 9> inches> / J 5 / 5 inches 9 inches / 9 5 / B> inches - inchesteen B> / > inches 5 inches

    Construction material choices

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    !etal%ngle Iron

    =roper angle iron is about 5mm thick and almost in eitherdimension. It is generally too heavy for bike trailers. #ou can getsmaller angle iron which is used to make signs used at road works soits easy to obtain. It measures about 3mm thick and 9 section.

    %nother type of angle iron which is lighter is the stuff with holes in10exion2 which is often used for industrial shelving. It is generallyabout mm thick and either s+uare or with one face wider than theother.&teel =ipe

    %nother easy to obtain metal for construction is conduit or steel water

    pipes. These seem to typically be 345 but apparently you can alsoget 9 and even 94. It is often galvanised so you there is a ma7orhealth risk associated with welding or using a grinding disk. If you aregoing to use it then you should sand off the 6inc and work in a wellventilated area, ie outdoors."ox &ection

    "ox section 4 s+uare section metal could be good to use. It should bemore resistant to buckling than angle iron. #ou find 9 s+uare +uite

    common / often found forming the frames of office desks4table etc.&maller sections may be found on some types of chair.

    &hopping trolley www.instructables.com4id4&hopping

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    www.instructables.com4id4"listering

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    trailer allowing it to be operated by hand separately from the bike.However, under braking 1especially with heavier loads2 there may bea tendency for the trailer to try to lift the back wheel. %rguably a hitchpoint near the rear hub is much more stable, although there arecontradictory schools of thought on this. (hen a bike turns the traileris at an angle to it and it brakes are applied while turning then thetrailer will push against the seat post and may cause the bike to 7ack