Rough conceptI'm drawing up a plan for a trailer, I've looked at quite a few online and some have larger wheels than others.

Does anyone know if a bigger wheel (or smaller) conveys any advantage to handling or anything else? I have spare 26 inch wheels and can get smaller ones.

It will be a single wheel trailer.

Update clarification, the idea is basically to chop up another bike removing everything except the forks and the bars in the picture and turn it around, then a bar to go over the bikes back tyre and attach under the seat.

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    A larger wheel handles bumps a little better. But height can also have a negative affect on stability. – Daniel R Hicks Jun 12 '16 at 2:03
  • @DanielRHicks any cons to smaller wheel apart from bumps? – Kilisi Jun 12 '16 at 2:15
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    You will have difficulty finding good quality wheels below 16 inches in diameter, and 20 inches might be a better target for that reason. – Daniel R Hicks Jun 12 '16 at 2:19
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    26" wheel should be no problem, first dude who rode the Canning Stock Route used an "ExtraWheel" trailer with a big wheel. All the usual (dis)advantages of big wheels apply and have been discussed here if you use the search box on the top right of every page. – Móż Jun 12 '16 at 3:34
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    @Kilisi tyre availability. If you have BMX kids in your area you should be ok, but getting decent quality tyres that will take more than 4 bar/60psi can be a challenge in remote ares - all you get are kids bikes with fat, low pressure tyres. Which are ok, but you will usually pinch flat them before the wheel fails or the frame bends. – Móż Jun 12 '16 at 6:43

My expectation with this design is that you'll be able to carry 15-25kg over a fairly rough track, if you built it reasonably well. Use the heaviest bike you can find as the donor, you want nice thick tubes. But it will probably fail by bending close to one of the joints. Bike tubing is not really designed to deal with bending.

With the design sketched I think that'll work fine with 26" wheels. The main thing will be welding the steering on the trailer frame/donor bike so it doesn't wiggle. Because the fork/wheel is going backwards the rake on the steering will be backwards, so if it's loose it'll be like trying to roll a castor backwards - very wiggly and unstable. Turning the fork round will help, but I suspect not much.

The suspension will probably not work as well as you hope because a fair bit of the force will be across the line of the suspension movement - rather than "brake dive" you'll have... nothing. I'd be tempted to try to get the fork more vertical, but that could end up making the design more complex and you're better off making something quickly, riding with it, then fixing the things that annoy you most once you have something that works.

Chainstays, your "bottom part", are really not designed to take bending loads, so that will be your weak point (assuming your welds hold). I would be tempted to brace those somehow, even just putting another tube between them with welded joints at the ends to reinforce that area will make the trailer stronger. If you have a space bit of tubing that would be well worth while. Gussets, BTW, will not help (here, or almost anywhere), they just shift the point of failure to the end of the gusset - designing an effective gusset is hard.

That ExtraWheel trailer design is all about a triangulated frame, and you could probably fake it using the seatstays and chainstays off two bikes, welded to a headset. It would probably be easier to build, but the attachment to your bike would probably be more tricky. I'd be tempted to bolt into the rack eyelets, if you have them, and see what happens.

  • Welding and bracing I can handle no worries. I'm not too keen on using the eyelets though at least not for more than an initial test, I have a much better idea for the hitch attachment. And after testing I'm going to try unlocking the wheel and spring loading it so it has a bit of turn each way, not much, but it seems useful rather than totally rigid.. Cheers for the info. – Kilisi Jun 12 '16 at 7:55
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    I'm looking forward to seeing what happens - can you post an "answer" here with details please once you've built it? – Móż Jun 12 '16 at 8:52
  • Yep, no worries :) – Kilisi Jun 12 '16 at 9:09
  • Also, if you can put a tube across the top, ideally by extending the head tube of the donor bike, you will make the whole thing much stronger. It will limit the height of packages you can fit in, but if you can live with that it'd help. – Móż Jun 15 '16 at 0:43

Wait for Moz' answer because he's build a lot of trailers.

The bigger the wheel, the better the trailer will roll over stuff. That is, a 16" wheel would hook up on a pothole that a 20" would just bounce heavily through, and a 26" wheel would take it in stride.

Assuming the wheel mounts direct to the trailer chassis, a 26" wheel bike would give you a level trailer with 26" wheels, or a slight downslope to a 20" wheel. Although in practice 26" bike to 20" trailer is unnoticeable while riding.

Height of load - you might choose to mount the wheel hubs above the floor of the trailer. This will ease loading somewhat, and will make the trailer more resistant to rollover on corners.

Given your intention is a single wheel trailer, you can consider the trailer's wheel as a spare for your front wheel. So I'd ensure the two wheels are interchangeable. Or you could use a second rear wheel, with or without a cassette, as a spare. The dropout width locks you into a front or a rear wheel. Front wheels are more common "spare"

  • Good info, my bike is a 29 so won't be using it for a spare wheel. In terms of load I'm actually grinding off everything from a frame with forks except the forks post and bottom part, turning it around and building the box part on it, so it will have a lowish clearance, still making my mind up how exactly to do it. Will fix the wheel in place to start with, and then maybe give it an inch or so turning ability each way later on springs somehow. – Kilisi Jun 12 '16 at 6:10
  • @Kilisi if you can make a sketch of what you're thinking of an add it to your question that would help a lot. Even a sketching using Paint or a cellphone photo of a paper sketch. "forks post and bottom part" isn't clear to me. – Móż Jun 12 '16 at 6:42
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    @Móż I gave it a shot, hope it makes sense. – Kilisi Jun 12 '16 at 7:04

your trailer design will be affected by wheel size. with a larger wheel, your load will be higher off the ground, but you'll suffer from increased weight, overall drag, and depending on design, varying degrees of wheel flop.

i would go with a 20" wheel size due to readily available high quality tires/rims from recumbents and bmx. in addition, you'd could also design a trailer with a two wheel axle in the middle of the trailer, which could help distribute your fore and aft load.

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    I'm going cheap, wheel quality doesn't matter too much, just going to grab one off a kids wreck, easily replaceable. I'm toying with a two wheel idea, but it looks harder to make and I'd need two identical bikes to cut up. – Kilisi Jun 12 '16 at 6:13
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    How high the load is off the ground is a design decision largely unrelated to wheel size. It may be easier to get the load lower with a smaller or larger wheel, but that depends completely on a number of design issues. Suggesting to someone who has asked for help with a one wheel trailer that they use two wheels without providing a reason why that differs from a one wheel trailer is also a bit pointless. – Móż Jun 12 '16 at 6:39

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