Harkin family HPV's:

Damian’s Challenge Hurricane SWB ASS Bike. 1999 Series model, 20” wheels Steel frame, Magura hydraulic rim brakes, rear suspension only. Very nimble (twitchy).

Sarah’s M5/Speedliner Blue Glide, SWB ASS Bike 1999 Steel Frame, Rear suspension, 20”/26” wheels. Very comfortable – scary to ride fast so don’t try!

Claire’s MR Components Swift Special Ex Murray Bridge 24-hour race trike. Very low seat angle. Fun commuter machine now with panniers.

Joan and Frances’ Flevobike back-to-back aluminum tandem 1998 Foam core and riveted aluminium skin construction with steel subframes. 26” aero wheels, two wheel drive. Magura hydraulic rim brakes. Separates in the middle for transport. There should be a suspension strut at the centre, but this bike has a rigid link bar instead. Quite an impractical bike, fast but scary to ride, limited gearing. Torsional frame flex causes an exciting “delayed steering” effect requiring great strength of character. Scares livestock and small children.

The latest edition to the Harkin stable the flexo bike - still in the development stages.

Here are some pictures of a bike I've been building - 'SwingBaby'.

SwingBaby is the latest outcome of my obsession to build a back-to-back tandem that can be split into two separate bikes. The previous plywood monster "ATB" (seen at Broadford last year) was too big and too heavy, so I've tried to simplify it. To achieve front-wheel drive and suspension, ATB mounted the whole front end on a suspended subframe. Chain tension can't affect the front suspension because the whole chain run is on the suspended part of the bike. This worked well, but introduced a zillion extra pivot points and WEIGHT.

I got thinking about Flevobikes. They have suspension and FWD and they're pretty simple. People seem to be able to ride them. So after reading Erik Wannee's excellent website, I decided to make something like the Knakker, but with suspension and a reversible drive!

The frame is 51 x 1.6mm ERW tube from Robot Trading with 5 mitre joints! The steering bearings are deep contact sealed ball bearings 30mm OD x 12mm ID. The head tube is 35mm OD x 2.5mm wall, 95mm long, bored out by Steve Nurse to take the bearings (Thanks Steve!). The yoke that surrounds this is cut from 100 x 50 x 4.5 Rectangular Hollow with a 12mm bolt down the middle. The rake is 45 degrees and there is supposed to be about 50mm of trail, but this varies with suspension movement. Pull the 12mm bolt and the bike falls into two halves which easily fit into my little Mitsubishi Mirage.

The back wheel is 20" with a wheelchair hub and a push-button axle (Tioga Comp Pool tyre). Front wheel is a small 16" with a Maxxis Hookworm and an 11-34 sprocket cluster. The wheels were made by Michael Rogan at MR Recumbents and were previously seen on the above-mentioned ATB. But now I've gone and added a Shimano cable disc brake from Greenspeed (Thanks Paul Sims!) .

Up front, the driving wheel is mounted in a frame that wraps right around the wheel - the 'PowerStick'!. The front end of this frame has a long stem or boom to which the BB shell is clamped. Thus, the whole transmission is self-contained on this part of the frame. A swing-arm pivot is formed by two 10mm rod-ends also clamped up to this transmission frame. By loosening swing-arm pivot clamp, the powerstick can be flipped through 180 degrees to drive the bike backwards (ie when it is being used as the back half of a tandem). The stoker will have to pedal backwards. Is this funky or what? I spent such a long time thinking about this!

The spring/elastomer is from a Birdy - bought from Cycle Science in Mitcham (thanks Peter Holloway!). I've ruined it by allowing the whole assembly to cock sideways, bending the spring as you can see in the pics. I'm going to remake the pivot clamp and spring seats to stop this happening in future.

The handlebars are from a folding silver scooter. The left bar carries the rear brake lever and can be easily unplugged to stay with the rear half of the bike. I've mounted the brake levers on bar-ends so that the cables come down vertically in the middle of the bike, clearing my legs. Also this helps me to ride it because my braking grip doesn't interfere with the steering. You have to steer it with your bum - trying to steer it with the handlebars is futile. I'll leave the handlebars on though, because they make it easy to pick the bike up.

When I build another one of these bikes, the two will bolt together at the back axle sleeves. The face of this sleeve is on the bike centreline, therefore the back wheel is currently offset to the right - more on this later… The big tubes running up under the seats will connect together with a heavy flange and some bolts.

I made the seat from three pieces of 3mm marine ply, laminated together whilst clamped down to the seat of another bike (the Flevobike tandem). It's held on with exhaust-pipe clamps from Midas.

Eventually, I will build a rear swing-arm with an elastomer suspension. The swing arm pivot will plug into the sleeve in place of the back wheel. The swing arm will be bent to bring the wheel back onto the centreline of the bike. So I'll have a choice between a symetrical suspended bike or a lighter lop-sided one. The swing-arm will not be used during tandem operations.

I can ride it! It took a few days to get going and I'm still very tentative. I rode 43km up at Maryborough with Robert and Jana Waryszak and I didn't fall off, but I did bail out a couple of times, slamming my feet down and hitting the brakes. I think it needs more trail. I rode it no hands for minutes at a time - it's actually more stable this way.

There are plenty of 'teething problems'. The 63 tooth chainring is very sensitive to chain angles. (You change down two gears and the chain instantly derails). I've currently got a nylon guide to stop this happening - I cut this from one of Joan's chopping boards (Thanks Joan!). The bike currently weighs about 15kg, but it ain't finished yet…

Damian Harkin 31 Jan 2006