Single Wheel Bicycle Trailer

My wife and I are avid tandem cyclist and love to tour. However, we are soon planning an extended tour of Tasmania and being a serious photographer, I wanted to bring all my best lenses... about 10kg worth. Considering we are ussually packed to the rafters (so to speak), we figured we needed to start looking into a trailer.

So, I started searching for a single wheel trailer for our tandem bicycle... After deciding they were way too expensive, still quite cheap overseas, but with the exchange rate and postage, it just wasn't affordable. I was left with only two possibilities... take less stuff... or build my own trailer.

So I built one... actually I built two. My first trailer was a two wheeler, but I chucked it out as it didn't work too well at all.

Note that most of the frame is made of 25mm sq aluminium moulding readily available in most good hardware stores. I got mine from Bunnings. Some stores also have some cool corner joiners and end caps. In total, the trailer cost me about AUD $200, but that includes all my mistakes. So in reality it's probably more like AUD $150. Either way, it's far cheaper than AUD $700 which is the current price for the BOB Yak's here in Australia.

UPDATE (30th March 09)
PLEASE NOTE - I've made a number of design changes since this website was last updated... I will upload some new photos and diagrams soon. The main change is the way it hitches to the bike. I have diverted away from hitching to the seat post, and now hitch to the rear axle. This resulted in a much more stable design, although a bit more difficult to connect and disconect from the bike. Stay tuned...

If you want to ask me some questions... feel to visit my website and send me an email. Just go to www.crisscrosscreations.com.au and click the contact us link.

Design

 Below are the drawings and photos of my first version of a single wheel trailer... The basic design concept is to have the bulk of the wait running under the rotational axis. Therefore allowing the trailer to self balance (a bit like a pendulum).

Diagram 1.1 shows the axis in blue... NOTE: the initial design was for a 26" wheel to match our tandem bike, but I also wanted to be able to swap it for a 16" wheel if necessary. The red circle shows the placement of the 16" wheel... As you'll soon see, I ended up running with the 16" as the 26" had too much flex and started to wobble. The other two diagrams (1.2 and 1.3) are of the upper support frame, and the lower tray (top view).

 
Diagram 1.1 - side view of entire design, showing rotational axis

Diagram 1.2 - Top support bar and forks

Diagram 1.3 - lower frame for tray

Version 1

Well... Here's the first attempt... fully packed and hitched to the bike. It worked fairly well, except for a nasty wobble (shimmy), which developed after slight corrections in steering. The wobble was controllable by slowing down, but still very irritating. If we were flying down hill at about 60km/hr at the time, it would nearly through us off the bike. It needed fixing badly.

Version 2... or at least with some slight modifications...

Modification 1 - swap 26" wheel for 16" wheel.

Modification 2 - adjust the way I pack the luggage.
Instead of placing all the weight as low and far forward as possible (ie. under the rotational axis), I felt that I needed to distrubute the weight along the axis... thereby minimising the centripical force generated by any rotational movment.

Result... perfect...

The first few photos show the trailer before I loaded it up for the first real test run. Notice the pannier rack on the rear... I tried using panniers, but it really upset the balance of things and I later removed it altogether.

Notice how I've packed the tray... That black bag on top, is my camera gear (heaviest). The orange one is our tent (second heaviest) and the blue, yellow and red ones are our sleeping gear (all the lightest items). Notice how the heaviest items now follow the axis from the hitch point on the bike to the spot where the tyre touches the ground.

The hitch...

The photo below shows how I've hitched it to the bike. The important part here is to understand that the hitch must stop all sideways rotation of the trailer... otherwise, the trailer will over balance and fall over. But it must still allow turns left and right as well as a limited amount of up and down.

Well... our latest test ride has proven a great success... the trailer has no interest in wobbling at all. And we can easily fly down hills and more than 60km per hour. I haven't tried anything faster than that just yet. But it shouldn't be too long...