Bickerton Portable folding bike
Updated 25 May 2018
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Recently I had a canvas bag, with a loose range of wheels and aluminium bits, deposited in my hallway. Gottfried asked if I could make any sense of the bits, which he obtained in exchange for a bottle of whiskey. It turned out that the bag contained a complete Bickerton Portable folding bike dating from 1979.
This was a challenge worth accepting as I had a few folding bikes in the garage, anyway. One more was not likely to be noticed. There was an owner's manual and some information available on the internet, which I have linked at right. I deposited the parts on the carpet in the garage. Gradually it started to look like some sort of bike. When I sat on it the seat stem started to collapse. Clamps were tightened more. I tried to ride the bike up a hill, but I was discouraged by the handlebars suddenly moving towards me. More clamp tightening gradually achieved a rideable bike. The tightening forces are not excessive, and some lubrication may help.
The Bickerton Portable folding bike was designed by Harry Bickerton in 1971. Harry Bickerton was an aircraft engineer in charge of design and development for de Havilland Aircraft. The use of lightweight aluminium alloys in the design of the bike is a reflection of its aircraft roots.
The modern Bickerton Portables folding bike is based on a Tern design. At this site there is a lot of original heritage material covering the history of the original Bickerton Portable folding bike.
1979 Bickerton Portable folding bike
The bike without the bag weighs 10.2 kg. The bag weighs 0.56 kg. The bike is rather high-geared, which suits flat locations, such as airfields. The 3-speed Sturmey Archer gearing is defeated somewhat by the 57-tooth front sprocket. The rear sprocket has 17 teeth. The bike is sold with a 13 tooth rear sprocket, which would be an impossibly high gearing for Wellington. On the flat it is a fast bike. Like the Brompton, it folds with the chain on the inside so it is clean to carry. The headset contains nylon components which contribute to the front-end flexibility. Some components are shown at right. The handlebars can be oriented to almost any riding position, from Dutch to aggressive.
The rear tyre is 420 mm in diameter and is marked as a 16 x 1 3/8 inch Michelin tyre. The front tyre is 370 mm in diameter and is marked as a 14 x 1 3/8 inch Michelin tyre. They appear to be the original tyres.
The Sturmey Archer 3 speed hub-gearing from high to low gear is 1.33, 1 and 0.75 times. Gear-inches are 73.90, 55.44 and 41.98 respectively. Metres-development are 5.88, 4.42 and 3.32 respectively. The Gain-ratios are 5.51, 4.14 and 3.11 respectively. These terms are defined here. The lowest gear is still too high for local hills.
There are two conventional ways of adjusting the Sturmey Archer 3-speed hub for smooth running. There is a threaded sleeve between the end of the gear-cable and the indicator-chain. Rotate it to tension or loosen the indicator-chain. The lock-nut should be loosened first. Set the trigger to middle-gear. Rotate the threaded sleeve so that the indicator-spindle, at the end of the indicator chain, is just exiting the end of the hollow axle. The second way is to set the trigger to high-gear and adjust the threaded sleeve, until the chain just starts to slacken. This may work better with a well worn hub. Tighten the lock-nut when finished. A third, unconventional method, is to note that a ticking sound is heard when pedalling in middle-gear and high-gear, but not in low-gear. A ticking sound will be heard in all three gear settings, if the threaded sleeve is not adjusted properly. As usual, Sheldon Brown has all the details.
The bike storage bag is rather clever as it can be domed up, to make a bag of several sizes. The bag can be hooked onto the handlebar and, when loaded, it may contribute to the stability of the front end.
Folding the Bickerton
Folding of the bike frame is done by moving the clamp-lever about 90 degrees away from the chainwheel. The tension adjusting arms can be moved out of the way and the bike folded. Other settings include shortening the handlebar, rotating it 90 degrees relative to the front wheel, and then folding it down beside the front wheel. When the bike is assembled four screw heads and four corresponding holes engage in the frame faces to increase rigidity. The bike should not be ridden unless both tension adjusting arms engage firmly with the clamp-lever. There are two nuts on each of these arms. The nuts can be adjusted so there is a tight engagement. The locking nut prevents the other one working loose. The clamp-lever engaging faces and the bearing surfaces in the frame should be greased so movement is easier.
At some time the bike has been ridden without the lower tension adjusting arm in place. This has placed undue stress and wear on the hinge and the four mounting bolts. One bolt, nearest to the front was partially fractured so I replaced it, and its neighbour, which proved to be OK. Normally the hinge and bolts would not be under any stress at all. When the bike is assembled it helps to support the frame from underneath, especially if the hinge is worn.
Riding the Bickerton
In Wellington I found the bike difficult to ride on hills. It was easy to ride on undulating terrain, as long as all the clamps were done up tightly. The Te Ara Tawa path proved to be an ideal route for testing. I was able to do a 12 km ride along this path with no problems. Riding around the Wellington waterfront was relaxed and easy. Paved river trails would also suit this bike.
Riding the bike reminded me initially of a stiff jelly. There is quite a bit of flex in the Duralumin handlebars, which could be interpreted as a novel front-suspension design feature. I have since added a brace between the handlebar clamps made from duralumin tubing, recycled from an old TV aerial. Duralumin is hardened, strong and is similar to current 6061 bike tubing. This has greatly reduced the flex in the handlebar. The new handlebar brace also stops the bike storage bag from opening in the wind. Some models have an additional protective bar, added to the frame, to allow sales in the US market. This is an additional, non-functional, complication which slows down the folding process.
Each time the bike is folded and unfolded it is unlikely that any settings will be the same as before. The unofficial record for unfolding the bike, ready to ride, is 30 seconds. Typically, several minutes are needed to get everything just right. Due to the wide range of clamp settings, the user experience is like riding the bike for the first time, every time. The best approach to riding this bike is to ride it in a relaxed style. It is unfair to be too critical, as the bike is 38 years old, and it still rides well.
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