Disclaimer: This is only a photo essay of my experience in an alternative bike design! I am not suggesting you build your own bike or copy this example! Save yourself the hazard and the hassle and go buy a folder at your local bike shop! Or you can ask your local framebuilder to look at this webpage and make one for you. But after looking at this they will probably say "no way", or "are you out of your mind?"
There is perhaps enough information here for an experienced framebuilder to make this (email me if any questions), but it would be quite a challenge for anyone else. A lot of work goes into a project like this. I could probably build a conventional bike frame in a couple of long days, but this one would take about a week. So many small parts that need to be brazed, and there is a lot of creative jigging to set things up. The result is a very reliable all purpose bike I would take anywhere, commuting, touring, dirt road or light trail riding. And it gets very small in about a minute and a half.
|What does it have? Built in front rack, bolt on rear rack, drop handlebars, fenders, front and rear generator lights.|
|Triple chainring, 135mm rear triangle with a 9 speed cassette hub and a rear disc brake. It weighs 31 pounds as you see it here.|
|It gets small in about a minute and a half. 27x21x11". Without the rear rack and fenders, it would be 19" wide instead of 21". Props itself up like this, or on its side. I can pick it up from anywhere and it all holds together.|
It's like a cross between the elements of a Brompton and BikeFriday. It gets smaller than a BikeFriday, and in less time, and holds together without needing a bag.. But it still has all the full bike features of a BikeFriday (drop handlebars, full range of gears, etc). It's not that much bigger than a Brompton when "folded", and does not take that much longer to fold it, but it is much more bike than a Brompton is.
The key here is that there is only one folding function on this bike: pushing the rear wheel under. The rest of the process involves separation of frame elements and clamping them together to form the "folded" package. That allows a frame design with less limitations dictated by folding requirements, and allows the use of standard bike componentry. Tubing is almost all cromoly aircraft tubes fillet brazed together. There is silver brazing where there are "lugs" (seat post extender, connecting tubes at rear of main boom tube). Geometry is pretty standard; 72-73 angles, 40" wheelbase, 25mm fork offset (short fork offset because of small wheels), 10.25" BB height. It duplicates the position I have on my regular big wheel road bike. Lots of low gears of course, and the 53x11 top gear is an acceptable 90". I don't spin out that often.
A 20" (406) wheel size is the best option for a bike like this. This tire size is available everywhere, from bike shops to variety stores, and there are lots of choices in this size from many makers. The Schwalbe marathon supreme 406-42 is a wonderful light, durable, and supple tire, and my current favorite. The front hub is a 74mm wide type found only on folding bikes. Formerly, I used the standard 100 mm wide hub, but now that high quality 74mm front hubs are available, there is no reason not to use them. It saves an inch on the width of the folded size, and that is huge. The front hub on this bike is a Schmidt SON XS 28 hole generator. The rear hub is a Shimano 135mm with a disc brake. 135mm is the standard mountain bike/internally geared hub size, and I don't want to be limited by a narrow rear triangle. The rear disc brake allows me to brake without wearing the small rims down. With rim brakes, I would wear out 3 rims a year, since I live in rainy Portland, OR. Sometimes the worn rim would just collapse, causing the tire to explode off the side. The front brake is a linear pull rim brake which I use only occasionally, for hard stops.
Folding it up
|next I take the seat extender out and fix the seat assembly against the side of the frame with 2 connecters I made.|
|Now I split the bike; loosen the clamps, pull the pin, separate halves of bike, and fix the fork against the frame with 2 other connecters I made. Also, I pull the wire connection for the tail light. Or if I forget it just pops out.|
|now I remove the boom tube and the handlebar stem. I fix the boom tube in place between the wheels.You can see the handlebars laying to the right.|
|Upper seatpost attachment. The short tube on the seatpost slides into the tube assembly that is clamped on the lower chainstay/pivot-pin tube (the one behind the bottom bracket). Almost all these little pieces in the following pictures are adjustable where they are clamped to. If I use a bigger tire (which would put the wheel in a slightly different place when kicked under) or different seat, I can adjust the pieces so they will still fit together.|
|This thing clamped on the seatpost has an arm that engages into the nut brazed onto the chainstay (vertical tube to the right. The bolt on the left provides friction so when I push it up and the tab enters the nut, it stays there.|
|seatpost assembly secured now.|
|Boom tube to seat tube connection. A nail drops thru the lower connection to resist pulling forces. If it was not there, the tube would slip out a couple of millimeters or so after some heavy pedaling. This pin (nail) idea has worked great over tens of thousands of miles. The holes have not elongated and the pin has not developed notches. There is probably a more elegant solution to this issue but why fix what is not broken.|
|Handlebar stem clamped on right side of front rack. Built in recess on the rack to accommodate the stem is seen here.|
|Left side of fork crown closeup|
|Upper left fork crown, with short tube (about 4cm long) projecting to the left. It is about a quarter inch inside the pivot pin already.|
|Fork crown alignment tube is now pushed all the way inside the pivot pin. The fork crown and rear pivot area of the bike are held together now.|
|The metal tab is pushed down behind the chain rail. This keeps the fork from coming out of the pivot pin.|
|The fork would still pivot forward or backward if not for this. Look at the 2 short horizontal tubes brazed to the fork leg on the right. They will engage with the chainstay when the fork is pushed into the pivot pin (fork is not pushed all the way in place yet, in this picture). That keeps everything solid. The quick release nut for the front wheel you see here is cut a bit shorter. It rests against the quick release nut for the rear wheel, also cut short. Brings the wheels closer together, making the folded package smaller.|
|Stem to fork connection. The same clamp tightens it on here and the on the steerer.|
|Tucked under a table.|
|fits almost anywhere.|
|To carry, I lean the leather saddle against my hip and hold the tube where the handlebar stem connects. Or I just grab the horizontal tube at the top of the folded bike.|
|Here is a airline legal size collapsible box I made. About 60 inches length/width/height added together. Limit is 62". Plywood sheets drop into internal pockets to assemble from flat.|
|When I remove the left pedal, the bike just drops in.|
|To carry stuff, a bag I made loops over both brake levers, and is supported by the rack below. A velcro strap fixes it against the headtube, if I remember to secure it (it isn't essential). The bag is about the size of a grocery sack.|