My uncle got in touch with me to ask if I’d build a tricycle for my auntie as a surprise birthday present. It would have to be able to cope with a gravelly farm track in South Wales, be a step-through frame design, and be 2-wheel drive. Er, yeah, no problem..
I found a Rogers bolt-on bike-to-trike axle housing, and had a 2 wheel drive cassette & axle made for it by Geoff Booker at Trykit. The Trykit axle and custom cassette body is a lovely bit of kit. I removed the bolt-on tabs from the axle housing, moved the derailleur hanger boss and brazed the housing onto the chainstays with 4 dummy bearings that my friend John Discombe made for me. A cold-drawn 18mm rod was placed through the slip-fit dummy bearings to keep everything aligned during (and after) brazing. The drive-side chainstay had to be bent to clear the cassette housing.
I used a flat surface with marked lines for centrelines, axle lines & BB lines (using another round bar on V blocks & dummy BB cups), and I also used a surface gauge and engineers squares. A digital protractor kept the seat tube at the right angle, and these adjustable V blocks were handy for levelling the rear axle alignment bar and to get the right BB drop:
I used a ladies’ lugset that couldn’t really give the angles I needed, so I ended up fillet brazing the hockey stick, and I ran into trouble with seatstay heel strike (trikes usually have mega-low BB drops as they can’t lean and the lower C of G is beneficial to handling, and I had unwisely opted for a lugged BB shell that limited my angles), so I built tabs off the rear axle housing to bring the seat stays way back. I drilled the hell out of the tabs to try and save a little weight. For a lot of the build I kept the chainset, a pedal and a shoe cleated-in just to be safe with heel clearance on the drive side.
Trikes always tend to follow the camber of the road, so low trail is preferred to minimise the effort needed for constant steering input. Seat stays are regular bike stays but used upside-down (thin end at the top).
I used 700c rims because the rear hubs that I salvaged from the ebay junker donor trike wheels had very small flanges with spokes that were already elbow-to head (they came with 26 x 1 1/4 rims – This is England!)
Also, I’m getting well stuck-in to production brazing at the Brompton Bicycle factory, and, way off-topic, but I was roped into playing bass in my mate’s “music video” about a fictional darts-playing character. I’m sorry:
Bye for now,