Shortening the trailer boom

We're going on a bike ride.
We're going to use the trailer.
What a beautiful day!
We're not scared.

Uh-uh! Traffic!
Fast discourteous traffic.
We can't go over it.
We can't go under it.

Oh no!
We've got to go through it!

Pedal pedal!
Pedal pedal!
Pedal pedal!

With apologies to We're going on a bear hunt by Michael Rosen and Helen Oxenbury.

Burley D'Lite folding Long before we bought the AnthroTech, we had a Burley d'Lite trailer, which was used to transport Michael to and from nursery.

Upright and trailer, picture

All photographs taken by Clare Macrae, or at least with her camera.
Except for this first one, a larger version may be obtained by clicking on each picture.

We chose the Burley D'Lite because of its excellent foldability (at the time we bought it, we had to store it folded up next to the 'fridge), and because of its size, fondly hoping to put another child alongside Michael one day.

(More information on our buying of the trailer can be found at Experiences with a child trailer)

Unfortunately, given Michael's ability to use up more than half the space inside all by himself, and our wish to put Thomas inside in a car/carry seat, this was not really feasible.

So, instead, we bought the AntroTech trike, fitting it with a child seat (courtesy of my brother- and sister-in-law in Germany, who no longed needed it) for Michael, and aiming to use the trailer for Thomas.

Before buying the trike, I conferred with Kevin Dunseath of D.Tek (from whom we'd bought the trailer) about whether it would be possible to fit the trailer to the trike. His considered opinion was that we'd be able to do it some way or another, so we went ahead with the purchase.

As it turned out, two things needed to be taken into account. The first, and simplest, was simply due to the lack of a rear triangle on the tricycle. Burley trailers have a rather neat fitting that allows them to attach to the rear triangle of an upright (or, indeed, some recumbents). This, of course, did not work with the AnthroTech.

Luckily, Burley do an alternative hitch, to address exactly this sort of problem, so it was merely a matter of buying the appropriate model and fitting it. Basically, this involved removing the left hand nut from the rear axle and fitting Burley's replacement, to which the alternative hitch then fits.

The other problem was down to me to fix.

For whatever reason (probably something to do with placement of the trailer relative to a bike on American roads where they drive on the right), the boom by which the trailer attaches to a bicycle is designed to offset the centre of the trailer from the axis of the bike. You can see the effect in the following diagram:

Upright and trailer, schematic

Unfortunately, when attaching the trailer to a tricycle, this effect means that that the trailer wheels are offset from the trike wheels, with the left hand wheel running outside of the track of the left hand trike wheel (I'm afraid you'll have to imagine the trailer wheels):

Trike and trailer, original boom, schematic

When I was buying the trike, I was aware that it would only just fit through some of the access points on the way to nursery and work. In particular, one constriction has between half and one inch on either side of the trike to play with. Unfortunately, with the trailer running off-centre, this wouldn't work.

Kevin and I had discussed this, and his suggestion was that, since the trailer boom is designed to work with normal uprights, which have relatively large wheels, it should be possible to shorten the angled part of the boom, bringing the trailer in towards the centre of the trike (and, of course, forwards, but that should be OK given the smaller wheel size on the trike).

Some quick comparisons of the trailer against the trike were confidence inspiring, and to clinch the matter I constructed a "pseudo-boom" out of some plastic piping, which I cut down as a proof-of-concept. Despite a tendency to twist (due to it being lightweight plastic tubing!), this reassured me that the project was possible.

So, secure in the knowledge that I'd already ordered another boom as a spare part (not only in case of emergency, but also so that we can switch the trailer from trike-and-alternative hitch to upright-and-normal-hitch simply by changing over the boom), I set to work.

In the end I removed about 15½ centimeters of boom - starting with a largish chunk and then progressing in half-inch slices. My aim was to centre the trailer on the trike's axis as much as possible - for this it was useful that our driveway is laid with bricks, giving nice lines to align things along.

The result was a trailer that followed within the trailer's width:

Trike and trailer, shortened boom, schematic

Here are two view of the "before" and "after" states of the boom - the boom attached to the trailer is the one I performed surgery on, and the one on the ground is the "spare" we use with Joan's upright:

long and short booms long and short booms

Finally, here are some pictures of the trike with child seat fitted and trailer behind:

trike and trailer 1 trike and trailer 4 trike and trailer 3

(Some more detailed notes on the process of shortening the trailer boom can be found in my "diary" of the early days of the trike - particularly Sunday 30 May 1999 and Saturday 5 June 1999. Also see Saturday 24 April 1999 for the preceding visit to D.Tek.)


Author: Tibs (tibs@tibsnjoan.co.uk)

Last modified: Wed Jul 2 14:13:17 BST 2003