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Saturday, December 4, 2010

An Inner Trailer


For a while now I've been mucking around with bike trailers and recently built one for carrying a large amount of shopping behind a folding bike. Unfortunately this trailer didn't fit on my recumbent and I wanted a trailer for my recumbent so you guessed it, the shopping trailer was due for the chop or rather "annihilation by jigsaw". And rather than building an ordinary trailer, how about one that trails from the front wheel of my bike? (My bike is well-qualified for this type of trailer, being long wheelbase, front wheel drive and having a really big space between the 2 wheels, more about it here:

So I began work. The trailer has a height limit - it will bang into the bike frame if its too high. Keeping this in mind, I mounted the trailer wheels on the back of the trailer box so the bottom of the trailer could be kept low allowing for reasonable depth. The box is made from unbraced plywood and is therefore a bit wonky and I will see about improvements at a later stage. The drawbar is a 28mm garden stake and it's attached diagonally on the base of the trailer.

Initially I thought I could just drill a hole in the drawbar and hang the trailer on a pin mounted on the front fork. I made the bracket on the bike, but when the trailer was hitched up it was too high and I couldn't pedal. Back to the drawing board.

Next step was to cut a small extra piece of garden stake and sandwich part of an old bike tyre between the drawbar and the new piece of wood. Apart from anything else, the extra bit of wood helps push the drawbar away from the wheel so the wheel doesn't bang into the drawbar during turns. The tyre was looped at the top and the loop was secured with a few screws, nuts and washers.

Then it was time for a few blockies to sort out any problems. The low ground clearance led to, you guessed it, scraping of the trailer base on the ground and I did a bit of work to fix that. My son Ewan took the main photo the next day when I was on my way to sell books at a book market. Trailer still way too low and lots of scraping, so en route I stopped and twisted the tyre which the front of the trailer hangs from to bring the drawbar up a bit. And this worked, I arrived, bike, self and cargo and trailer intact at the book market.

While at the bookmarket, I readjusted the loop at the front of the trailer and the whole thing worked very well on the way home.

Well what I have here is certainly exotic - an exotic trailer on an exotic bike. Here are some of the advantages and disadvantages of the design.

* Wheels on the trailer are at the back. When compare to a 2 wheel trailer with wheels in the centre, the trailer hitch bears weight and the drawbar must stand more bending force. The bike is front wheel drive so weight on the front wheel is a good thing - there was no wheel slippage when climbing hills.
* This bike plus trailer is much shorter than the standard trailer arrangement. As well, the trailer following behind is very low and would probably need a flag for it to be seen by drivers peering over car bonnets. With the trailer in the centre, a flag is not needed.
* Having the trailer in the middle restricts the height and length of the trailer. Extra volume can be achieved by having a wide trailer, but this starts to make getting on and off the bike difficult.
* Once in motion, the bike and trailer handled ok. But starting was a bit harder than normal, I had to sit on the bike and start pedalling from a standstill. Normally I can start walking or running, then leap onto the bike side saddle and get going that way.

* The current trailer hitch allows the trailer front to "pendulum" about the hitch on the front. There is little resistance to motion from the trailer wheels at the back, so the whole trailer can move back and forth relative to the bike during acceleration / braking creating a not unpleasant "trailer surge" phenomenon.

* Not for the shy and retiring!

* Here is the video

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