Cyclaholic

This is my attempt at a single wheel trailer. Those of you that have attempted a d.i.y single wheeler will appreciate the difficulty and complexity compared to a two wheeler.

I have used dumpster rescued materials as much as possible, but for this project I had to buy the tie rod ends. the Action Packer tub is one that I've had for years and have used on a previous 2-wheel trailer project. I enlarged the cargo area of that trailer and sold it, but kept the tub for this project.


Chassis design is in 1" square tube. Rear wheel sits in a road bike fork.





That's a 26" hybrid fork and 1" threaded headtube with the original head bearings acting as the main lateral pivot axis between the trailer and the bike. The steerer tube on the fork was cut off and welded back on at 90 degrees.



The dropouts were cut off the end of each fork leg. A high tensile bolt was welded on each leg, to mount a tie rod end. The length of each leg can be adjusted then locked in with a nut. This allows fine adjustment to allow for assembly inaccuracies and line up the trailer with the bike.


The bits that go on the bike. These parts need to be designed for your specific frame. I used the fender mounting point to secure the plates against lateral torque forces - something that you don't have to deal with in a 2-wheel design. The friction between the plates and the frame is nowhere near enough to resist the lateral torque.








A bad pic of the trailer hitch..



The final product with a very happy little boy that got a (very slow) ride in the trailer.



Performance-wise, I've used it multiple times for groceries.

With no load it tracks perfectly true behind the bike but can get a bit skittish in fast cornering on rough ground. however, you'd already be cornering dangerously fast even if you weren't towing a trailer, and most two wheel trailers would have already rolled over at those speeds.

Anything up to 35 - 40 pounds and it tows rock solid with no handling vices or influence on the bike provided the load is as far forward in the box as practical. The further forward, and low, you can place the load the better it tows. At the sort of speeds a sane person would do, it's unaffected by mid-corner potholes.

As the weight of the load increases over 40lb the handling starts deteriorating. The most I've had on board was 65 pounds which was just dangerous at anything over fast walking pace. The further forward you keep the load the better it handles.

The lower resistance (part aero part rolling resistance) advantage over a typical two wheel trailer is readily apparent if, like me, you like to move fast when towing a light load. The hitch system is absolutely solid with no slop and no binding around the pivot points. I'm very happy with the results, it turned out even better than I expected.

If anyone would like details beyond these pictures just ask, I'm always happy to share. Feel free to duplicate any/all aspects of the design.... Now I just have to get around to cleaning it up and putting a coat of paint on it.

Cyclaholic

Here's a couple more pics of the finished trailer...

Nightshade

Good job, mate!

Is a paint job in this trailers future??

couchman

nice

CsHoSi

Wow, great work! Thanks for the write-up, saved for future reference.

Sturmcrow

Could you have cut the donor headtube down a bit with a corresponding shortening of the donor steertube to get a little more clearance there? It's hard to tell from the photos, but it seems like you could have some clearance issues when riding off a curb.

Looks like a great project. With those wingbolts its practically quick-release.

jdmitch

ditto

istomtom

Very nice.

My only concern would be the ground clearance below the top (now bottom) of the headtube. When I've pulled a single wheel BOB trailer with my mtn bike I've taken it over 5" rounded curbs. That headtube on yours would bottom out on an obstacle more than 3 or 4" it looks like. Just a thought but not an issue if you're not pulling over obstacles.

Cyclaholic

Clearance under that headtube will be a problem going down gutters (going up is OK). I don't normally go up/down gutters when towing a trailer, but I can see how it could be a problem. the more I look at it, the less I like that headtube bearing hanging down there waiting to get bashed into something.

I don't want to do any modifications just yet because I'm going to put a Schwalbe Stelvio high pressure road tire on it and get out for a 4-day long weekend camping trip with a few buddies, in a few weeks. I'll probably carry about 40lb of gear and do maybe 200 miles on the bike through a whole bunch of different terrain. When I get back I'll have a clear idea of what needs to be modified..... and I'll put some paint on it after that .

Should I put this build into the "Trailer design tips" sticky thread?... or maybe a moderator can merge this thread into that one if you guys think it's worth keeping for future reference?

astronomerroyal

Yes, yes, you should put this in one/both of the sticky threads. I almost missed this thread because I usually just visit the stickies.

It's a very nice trailer - beautifully proportioned. I'm going to be the Devil's advocate and ask why you think it's more difficult to build than a two wheeled trailer. I've only built two-wheeled trailers, but it seems the Universally agreed upon difficulty is the hitch - the design of which for one-wheeled trailers (like yours, and BOB's ...) is essentially perfected. However the currently popular side-arm design for two-wheeled trailers is less than perfect (in my cringingly humble opinion) - which is why it might seem easier. I think the perfect hitch for a two-wheeled trailer may actually be more difficult to make, and is so few people attempt it.

Certainly the trailer bed has to be more rigid in your case. I'm guessing the trailer weighs about 30lbs.

Could you possibly expand (maybe just bullet points)?

If I make another trailer it may well be one-wheeled, so I'd like to know what I'm getting into.

Many thanks,
AR

Unknown Cyclist

That behaviour sounds like it's tyre pressure related.

If it's behaving under load but is 'a bit skittish' with no load I'd guess the tyre pressure might be a bit high for unloaded use.

With no load it doesn't need to be anywhere near as high as the cycle tyres as the load on it is much lower.

Lift the trailer up a few inches and drop it, see if it bounces.

Nitram

Looks pretty awesome. Wish i could knock something up like that!

Cyclaholic

Ok, I'll copy & paste the original post into those stickies.

This is my 4th attempt at a single wheel trailer design. The first 3 were successful failures (successful because of what I learnt from them). In each case it was the hitch design that brought me unstuck.

In design, the difficulty is in dealing with the way loads are transmitted through the hitch mechanism without making it too heavy or losing rigidity. For example, if the trailer has a load and the C.G. of the trailer + load doesn't fall on a line between the hitching point and the trailer tire contact patch then a torque force between the trailer and the bike is generated during cornering. Any torsional flex in the chassis or worse, the hitch, can cause you all sorts of weird handling. If the load is big enough and/or the speed high enough, it can easily become dangerous. Then there's the fact that you have two degrees of freedom, but each DOF is separated along the hitch, and each one needs to pivot freely while remaining rigid in the other axes.

The difficulty in construction is in getting everything lined up without dedicated jigs. The symmetry of the hitch system is important in this design.

I would respectfully disagree there. I sorted out a successful two wheel hitch design on my first attempt, and IMHO it's superior to most commercially available designs.

I'm interested to know why you think the side arm design is 'less than perfect'? (not calling you out, I genuinely want your thoughts).

Personally I think the side arm to the rear axle is actually pretty good even though it doesn't look as sexy. Purely from a mechanical design viewpoint it's actually a 'better' design than the single wheel trailer hitch. For example, it places lateral loads much closer to the bike's C.G. so any forces on the bike happen at the end of shorter moment arms and therefore have less effect on the bike's handling. Also, the two wheel design doesn't put any significant proportion of the cargo load on the bike (i.e. the hitch), although that's a property of the overall trailer layout, not just the hitch.

It came in at 22lb ...in aluminum I'm sure I could knock another 5lb off it.

Go for it! I love seeing the amazing stuff that pops up in this forum. If you want more details on any of the specifics of my design just ask, I'm happy to share.

Cyclaholic

That's a good point. I tend to keep the pressures up on the high side.

Thanks for the tip.

Unknown Cyclist

Let me know if it works

I had a pivoting sidecar that used to bounce on uneven surfaces and drag the backwheel out of line on bumpy roundabouts until I dropped the pressure a lot.

Of course too high pressure doesn't affect handling in a straight line....

Cyclaholic

Mate, you can. You're in Newcastle - I think it has the highest concentration of MIG welders per capita in Oz!

wade200

awesome! I've been wanting to build something like this but lack the welding supplies.

Dan Burkhart 

Nice work
As far as the handling characteristics, I think it could be improved by putting a bit of rearward tilt on the pivot. Because a one wheel trailer hitches to the bike in such a way that there is roll coupling, it seems intuitive to me that angling the pivot would create trail, and improve stability.
If you look at a BOB trailer, you will notice that there is a noticeable angle to the pivot, and I can say from my own experience that the BOB is very stable under all the conditions I have put it through.

Nightshade

The little boy would be much prouder of Dad's work if had a decent paint job so it didn't look so
cobbed together and amaturish.

BossCat

Nice build. I have just finished a one wheeled trailer. It was knocked up in an afternoon, the rest of the week was spent sorting out the odd teething trouble. Its going ok so far but I need to test it out with some weight in box.

See here..... https://www.bikeforums.net/showthread...=326435&page=9

Tom

Doconabike

Cyclaholic,

Thanks for posting the great trailer idea. It looks very practical.

Do you mind posting what type of welding equipment you used? I am a beginning student in a metal working class and am getting comfortable (not talented, but comfortable) with oxy-acetylene welding. We start on stick welding and MIG welding next term.

Here's a fun little bike parking rack I just made with the oxy-acetylene torch and some scrap pipe.



If you have time, could you explain what type of welding you used and talk about any specific issues that come up when you are doing projects with old bike tubing and frame parts.

Thanks,
- a beginning bike hacker and welder

Sturmcrow

Dang, that's beautiful! Very organic.

rock_ten

This is great, and I have the pieces required. The hitch will be trouble for me, though, since I can't make custom pieces like you have. I basically have a hacksaw, and then I'll be taking the pieces to someone else to weld them for me (at a cost). I'll be using road-sign angle iron for the frame, like BossCat did.

Speaking of BossCat's design (https://www.bikeforums.net/showpost.p...&postcount=221) do single-wheel trailer need to be hinged in the vertical plane like that? From what I can see of commercial trailers like that, they're not - or am I wrong there?

I think for a hitch I'll need to make something to clamp onto the chainstay on either side.

I will be using this for my courier business and so hopefully I can make it look as sleek as possible!

I'll see how I get on, not sure if it will all work really. I'm sure I'd be better off just buying one, but I'd feel uncomfortable doing that.

BossCat

Rock_Ten,

What ever you do dont copy my HITCH design! The hinge part is flawed -(any weight in the box makes the front wheel of bike lift of the ground). Have a look at these trailers, they may give you a few ideas how to do the hitch.

I like this trailer.

https://www.instructables.com/id/new_...eted_march_09/



A couple more for you to consider...

https://www.instructables.com/id/Sing..._Bike_Trailer/



https://www.instructables.com/id/Fast..._Bike_Trailer/



Iv'e had a bit of a redisign of my hitch but have still to test it out, so no photos as yet till I get it working
Best of luckwith your build
Tom

rock_ten

Thanks for the help! Those other designs are nice, and the seatpost hitch is so tempting, just for simplicity's sake. But I feel that they look somewhat more lumbering and less stylish, so I need to have the hitch lower down, unfortunately. I am currently entertaining the idea of buying my own welding gear, there's some stuff quite cheap around here. Probably for about as much as it would cost me to have someone weld two of these trailers together I could buy my own equipment.