Fancy a Threesome?

The trip to the mecca that is Balcatta Tip yielded 3 promising, sturdy, steel mountain bikes for the gand sum of AUS$20. Tim also found a rather fetching small pink racing bike in a separate skip, which he took for his own purposes.

The captain's bike is a large 'Repco Legend' mountain bike with a classic horizontal top tube and narrow steel tubing. The only drawbacks with this frame are the American style Ashtabula one piece crank and bottom bracket and the odd sized, very large chainset (48-42-36). We need same sized chainrings to link the cranksets together.

The middle frame is possibly the best of the three, although this is faint praise. The 'Sportsworld Trailblazer' is another narrow steel tubed, horizontal top tube mountain bike, 2" smaller than the lead frame. Ideal. Tim eagerly stripped this bike before I got a chance to photograph it.

The stoker's bike is a real pig. It appears to be a 'Bad Attitude Hype', but there are several other stickers on the frame. In an early 90s attempt to copy Cannondale it has oversized tubing. However, instead of being made from lightweight aluminium it is steel. This ruggedness appealed to us as this frame will be taking the greatest loads. John also liked the sticker that said Dude.

First cut is the deepest

Some precision engineering

After stripping the frames down of their laughably bad parts we were ready to start cutting metal. Fortunately not too much precision is required at this stage and it was simply a matter of splitting the head tubes and removing the seat stays on the rear frames. With worrying gusto Tim set about the bikes with an angle grinder.

A touch of gentle percussion engineering later and the head tubes fitted snugly around seat tubes of the preceeding frame. Sweet. This was our first real chance to fit the frames together and see if they would work. The initial prognosis is good with all bottom bracket heights seeming acceptable. There may be a requirement for two of us to shortern our arms a bit, but we'll deal with that problem when the frame is welded up.

Using string to align the frames

Not pretty, but strong

Before welding commenced we cut and shaped the braces to be added between the bottom brackets. These were formed from very strong chromoly steel. We knew that that the chromoly was strong as the hacksaw made little impression on it. This was in stark contrast to the short work it made of the steel-brie alloy that the old frames are made of. Once cut to length fish mouths were shaped into the ends so that they would butt snugly against the down tubes.

The first frames to be welded together were the front and the middle. A great deal of care was taken aligning them. The two methods we used for this were running string around the frames and matching the offsets on each side and judging by eye. The latter of these caused the most discussion between the three of us. First welds were around the head tube/seat tube interface before inverting the frame and adding the braces. The braces sleaved over the stubs of the chainstays that we left on the frames. The process was repeated to weld on the back frame.

Initially we are very impressed with the complete trandem frame. It is very strong and stiff and not even that heavy. A coat of paint and she'll look bonza.

The re-spaced double chainset in position 2

The single 38t Ashtabula chainring at 1

We got lucky with the chain length from middle to back. By running a standard width derailleur chain around the respective granny rings we were able to still use the middle and large chainrings at the back to drive the rear wheel with no clash of chains and minimal requirement for chain tensioning.

We were not so fortunate from middle to front. We had originally intended to connect the large chainrings but, even with a half link, we had a lot of slack in the chain. We were reluctant to use a mechanical chain tensioner (such as a modified rear mech) and the chainrings were too large to use a ghost ring.

A further trip to the tip yielded an Ashtabula chainset with a 38 tooth middle chainring which we swapped onto the cranks on the front bike and connected this back to the middle. There was no improvement in chain tension but at least we could use a ghost ring with these smaller chainrings.

Unfortunately because we were using a wide BMX chain, with the half link, there was now a clash between the chains going back and forward. This was solved by grinding the the middle chainset apart, discarding the now redundant large chainring and re-spacing the middle ring. This assembly was bolted back together with large M8 bolts.

While we were in the mood for cutting, we also discarded the small and big chainrings from the front.

The chains actually stay on without any tensioning, but the ghost rings improve the affair and look kinda cool.

A serious consideration with tandems, let alone trandems, is overheating the rims when braking and blowing the tyres. This is potentially very dangerous. Disc or hub brakes are highly recommended. Sadly we couldn't find any of them at the tip so we will be going with whatever we can find.

For a given speed, on a constant slope the energy generated in the rims has been calculated. If you want to be bored by the inappropriate application of lots of GCSE physics, click here to see a pdf of the full calculation.

The chart to the left summarises these results. Although no cooling of the rims has been considered, it clearly shows that if we reach 50km/hr on a 10 degree hill we will be transported back to 1955 where we will have to act as matchmaker to our parents to save our very existence.

The emergency caliper brake. The canti has now been upgraded.

In the end we were kindly given some good quality V brakes and levers by Neil and Meg O'Leary. They may have saved our lives as all the cantis on the tip bikes were pathetic. Both these brakes are both controlled by the captain. We had to buy a special 3m tandem brake cable at huge expense ($9). The alternative, having someone at the back who couldn't see where they are going in charge of the brakes, didn't seem like a great idea.

In addition to this fairly conventional set up we have installed a safety brake on the rear wheel. This is a caliper brake attached to the wrong side of the chain stays with a lever going up to the tail gunner. This brake is for emergencies only, should the long cable snap or the 2 V brakes not provide enough stopping power. It is fairly ineffective, but gives number 3 a psychological crutch.

The homemade stem

However we failed to find a second stem like this so Tim made one by cutting the handlecar clamps off of 2 quill stems and welding them together at right angles. Angles were measured accurately with cold forming used to make minor adjustments.

Two sets of riser bars were used as these allowed us more adjustment to fit our gangly legs into the somewhat cramped cockpits.

Painting the frame hanging up

Applying the transfers

The next stage was to strip the frame down, clean it up and paint.

Removing all the old stickers and tidying up the weld splatter required lots of tedious scraping and sanding. John was conveniently working offshore for this phase.

We were dismayed to discover that Hammerite is not available in Australia. Some similar, inferior, metal paint was purchased and the desired burnt orange shade created with some careful mixing.

Initially the paint didn't seem to be covering the mess of original bike colours, bare metal, rust and messy welds. However the third coat did the trick, giving a great glossy finish.

We had some stickers inexpensively made up by a sign writer, as the finishing touch.