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Folding bikes are handy, but slow and boring for daily commutes. Singlespeeds and fixed gear bikes are quick and fun, but cumbersome and expensive to travel with. So, my aim was to build a quick, fun, compact, full size, single speed bike which I could pack:

  • in two suitcases;
  • in the back of a small car;
  • as a folding bike on a train (they can be taken on the train for free here);
  • as regular checked baggage on a plane (to avoid bike fees that exceed ticket price).

The objectives were simple but strict. The bike had to be as light, but just as rigid as it was before modification. Furthermore, one should be able to take it apart and put it together within twenty seconds (on a moving train). Also, the modification had to be done without any welding (or power tools for that matter) and for less than 100 euro's. Impossible? No. Challenging? Yes.

While it took quite a bit of time to come up with a system, the process is actually rather straightforward, requires no special skills (besides a fair bit of elbow grease), and I stayed within budget.

Why build this yourself if you can just buy these beautiful stainless S&S frame couplers?
Because they cost $400 to $600, and that doesn't include installation. Which must be done by an official retailer, which isn't available in my country. So we're looking at an investment of over $1000. For a forty year old bike :')

Disclaimer
The author of this Instructable takes no responsibility whatsoever for anyone or anything getting damaged by building, riding or even looking at a bicycle inspired by this Instructable.

Step 1: Sourcing a Bike

While it's tempting to get any old beater, I'd advise you to pick your bike carefully. An old racing bike in a decent state works best. As you’re going to reuse most of the parts, get one in an overall good condition. Rear sprockets, shifters, rear brake and most of the cables will be discarded, so they can be worn. I chose to replace the front brake and the chain as well, but that's up to you.

Make sure that the frame is straight, has horizontal drop-outs, the wheels as straight, there's not too much rust and the bearings are okay (though they're cheap to replace, so this isn't a deal breaker per se). For more info on finding a suitable bike, have a look into one of the many Instructables about converting a racing bike into a fixie/singlespeed.

I opted for a seventies ten-speed Koga Miyata, the main reason being that I got it for free. It was in good nick, though repainted badly in an ugly colour and the derailleur was stuck. (The bike in the pic is a reference, I wouldn't dare to cut that in two).

Why can't I use my oversized aluminium bike/carbon mountain bike/grandmothers wheelchair?
You probably can, but it makes the conversion exponentially more difficult. As we're doing this without a welding apparatus, there's less room to make things fit. The scaffolding couplings are available in several standard sizes. 42mm (inner diameter) and larger is mostly used in scaffolding (duh), but that's larger than most bicycle frames' outer diameters (note: the top tube and down tube often have different sizes, I'll get back on that). Plus, it's rather heavy. Different combinations might work; the key is to find a good fit between the couplings and tube size. The 27mm (about 1") "scaffolding" coupling comes close to the standard tube sizes for many classic bicycles, which makes conversion a lot easier.

This Instructable assumes a standard frame tubing size for many classic racing bikes: 28.6 (1 1/8") x 0.8 mm for the down tube and 25.4 (1") x 1.0 mm for the top tube. The catch is that you don't know the wall thickness until you cut it up, but the inner diameter is slightly less important or can be mitigated with some standard parts from the hardware store.

Found a decent bike? Now let's find the couplings!

Step 2: Sourcing the Couplings

As stated previously, we'll use 27mm scaffolding couplings. These are probably not found in the construction section of your local hardware store, but in the furniture making aisle (or online). Making furniture out of scaffolding boards and steel is totally hip, but people want them to be sufficiently refined for the living room. That's why hardware stores carry these 27mm tubes and couplings, which are probably to flimsy to build even a small platform. But they're perfect for our purpose!

A key feature of the design is that the forces on the bike are cleverly distributed in the coupling. A sleeve joint coupling (see picture) seems to be the most simple solution, but it's guaranteed to fail. The down tube, 'pulls' on the coupling under the weight of the rider. This creates considerable force, especially when you hit a bump or pedal hard. A sleeve coupling that tries to keep things together with only one clamping bolt will make sure you'll end up in the hospital. Plus, to get sufficient rigidity, the fit must be so tight that you wouldn't be able to take it apart and put it back together without a mallet (you'll see why in the next steps). And beating you bike up with a mallet would look weird, wouldn't it?

So, the way to go is a so called short swivel tee and a short piece of pipe. You can secure this coupling securely to the frame ends and it distributes the lateral (?) force nicely across a piece of sturdy steel tubing.

You should be coming back from the hardware store (or the post office) with:

  • Two sets of short swivel tees for 27mm 'interior scaffolding'
  • One short piece of 27mm tubing (mine was 25cm)
  • Optional: a key for the hex bolts (my bolts are imperial, all my tools are metric)
  • A big smile because that wasn't that expensive at all :)

Got yourself the hardware? Then let's cut!

Step 3: Preparing and Cutting the Frame

The first step is to strip the bike of all it's components. Make sure to keep the ball bearings together and keep them free from dust. (Pro-tip: labeled zip-lock bags.) If you plan to repaint the frame as well, this might be the point where you sand, clean and smooth the frame. Repainting gives you the opportunity to grind off all the lugs for cables and other stuff we don't need after conversion.

Measure the total length of the coupling when it lies flat on the table with the piece of pipe bolted in. Then unbolt and measure then maximum insertion distance for the tubes in the couplings (see picture). This is easy to do by measuring how far you can stick the piece of pipe you bought into the coupling. The total length - (2 x maximum insertion distance) gives you the size of the piece of frame you'll replace with the coupling and thus the piece you need to cut out. I ended up with about 58mm.

The coupling should be fairly close to the back of the bike to end up with two (somewhat) equally sized parts, but not too close as you want to stay away from the sprocket and the seat tube and have some space for handling you key. Now, measure and mark the location where you want to place the coupling. Measure again, and put a piece of masking tape on the frame where you make the cuts. Measure again, say a prayer, and cut your bike in two. In total you'll be making four cuts.

Congratulations, you've passed the point of no return! Now you have a disassembled bike with two gaps in its geometry and two small pieces of tube. Don't throw the pieces of tube out! We're going to use them in the next step.

Step 4: Mounting the Couplings

If you have the same frame diameters as I have, then the piece you cut out of the down tube will fit over the top tube, and the piece of top tube will fit inside the down tube. We're going to use this to reinforce the tubes before we slide on the couplings. For that, we need to cut the pieces in two, so we end up with four rings, about 25mm - 30mm wide.

If you have different diameters, you're on your own here. Luckily, there are tonnes of different steel pipes in the hardware store with different inner diameters, outer diameters and wall thicknesses. Grab a calliper, a notepad and the pieces you cut out and you'll find something to make adapter rings out of.

While the couplings are sold as 27mm couplings, their inner diameter is actually quite a bit wider. They are designed to accept 27mm pipe easily, so mine had an inner diameter of a bit over 28mm. Perfect, as our down tube is 28.6mm!

The down tube
To reinforce the thin steel of the down tube, glue the rings you made out of the top tube into the down tube (see picture). Any glue will do, as they will be compressed by the hex bolt later anyway, which keeps them in place. I used regular contact glue. Use a half round file to make the opening of the coupling round (trust me, it isn't). Press it onto on of the down tube endings every now and then, hit it with a mallet and see if it fits and where it leaves marks in the steel. File a bit more if it leaves deep marks. Don't file away too much material, as you need a very snug fit to retain rigidity. When the coupling moves about a millimetre after a hit with the mallet, you're probably good to go.

Now comes the tricky part. Put the piece of tube you bought through the eye of one of the halves of the coupling and bolt it tight. This gives you a handle to keep the coupling halve straight when you use the mallet to get it on the tube. Repeat the procedure for the other end of the down tube.

The top tube
The procedure for the top tube differs slightly, as the rings will be on the outside now. Adjust the opening of the coupling the same way you did for the down tube, for it to accept the rings. Place the rings on the workbench, put one half of the coupling over it and use the mallet to gently ease it into place. Then slide the assembled coupling halves on the top tube and align them.

Alignment and creating the middle pieces
To ensure easy (dis)assembly when it's done, make sure the two pieces of the frame align nicely and the piece of pipe is completely horizontal when you put it in. When it is, bolt the couplings to the frame (tightly!). You can slide the piece pipe over the end of the hex key to get some extra leverage. (Don't hurt yourself). Then cut two pieces off the spare piece of pipe, having the width of the assembled coupling. When you're done, it should look a bit like the last picture.

Step 5: Secure the Couplings

When the couplings are in their final position and the hex bolts are properly fastened, drill two 4mm holes through the bottom of each coupling. In the unlikely event that the hex bolts won't hold, small bolts will keep the frame from coming apart at speed.

Uncoupled, you should have just enough access to drop a (self locking) nut in there and position it over the hole with you pinky while you put the bolt through from the bottom. Then stick a spanner in there to secure it properly. It requires a bit of fiddling, but it should work. An easier method is to use a tap to thread the hole so you don't need a nut inside the tube. But I didn't have a tap, so I took the took the fiddly way.

While you might be tempted to trust the big hex bolts, picture how you will crash if one does decide to give way (spoiler: it'll be ugly). So don't skip this step.

Step 6: Painting

Ordinary spray paint will suffice to give it a nice look, although keep in mind that it is not nearly as tough as the original paint. I won't go into detail here, as there are plenty of tutorials online on how to paint a bike. There's no need to paint the coupling as they are already rust proof and the paint on it will damage anyway. Plus, they are the key feature of the bike so they should stand out!

The front fork isn't in the pictures, as I painted that before when I had to paint some other things matte black.

Tip: don't forget to mask the tread of your bottom bracket, the inside of the seat post and the inside of the headset.

Step 7: Assemble and Ride! (or Disassble and Pack)

From here on, it's all pretty straight forward. Check some other tutorials online on how to adjust the various bearings, get a straight chain line, et cetera. Secure the small pieces of pipe tightly in the couplings on one end of the frame, and use the other end to bolt and unbolt.

I rebuilt the bike with only the smaller chain wheel of the two, and I placed it on the inside of the spider (the thing that attaches the chain wheel to the crank) instead of on the outside where it originally was. This gave me just enough clearance from the frame (3mm), and a straight chain line without re-dishing the wheel.

While I originally intended on riding fixed gear, I found that free wheels are better suited for daily commutes. So the rear chain wheels were replaced by a simple BMX freewheel and I put a gold coloured single speed chain on (ya know, for blingz).

The bike was originally equipped with old centre-pull brakes that required a bracket on the stem, and they were quite worthless anyway. As the modular design allows no rear brake, I shelved out some money for a proper front brake and brake lever (both Dia Compe). Well spent money, as I would've crashed it many times by now if I hadn't.

Step 8: Costs and Experiences

While projects like this usually tend to cost more time and money than planned, in this case the latter wasn't true.

  • Bike (donated): 0
  • 2x Short swivel tee: 23,98
  • 250 x 27mm Scaffolding pipe: 3,29
  • Paint and sanding paper: approx 10,00
  • Dia-Compe 806 DP front brake: 17,99
  • Dia-Compe Dirt Harry brake lever: 22,95
  • KMC Z510S Gold chain: 9,95
  • Freewheel (eBay): 3,50
  • Ass Saver rear mudguard (I love this thing): 7,99
  • San Marco Rolls vintage seat (salvaged): 0

Grand total: 99,75 euro!

This doesn't include the bike, but does include the upgraded brake and some luxury items such as the mudguard and the chain. If the paint of your bike is okay, you're okay with the cable guides on the frame and the brakes aren't too shabby, you could do this conversion for about 30 euros.

As one of the commenters remarked, the original chain is made to hop off the chain wheel and a singlespeed chain is not. While I encountered no problem with chains running off the chain wheels (if the chain line is perfectly straight, that is), it is advisable to spend a few bucks on a singlespeed chain. Singlespeed chains are also more robust, last longer and come in all sorts of fancy colours.

Experiences

I've ridden the bike for a couple of months now, taken it on the train a dozen times and gave it some serious abuse. Apart from some scratches on the paint, it holds up really well. No sign of bolts loosening and the frame feels as rigid as it was before. Train conductors frown, but don't complain. Though seeing someone take a bike apart on a train is quite the conversation started for other passengers, apparently.

Feel free to post any questions in the comments!

Edit: thank you all for the wonderful comments on this project! I'm happy and humbled to see that almost twenty-five thousand people have viewed this Instructable, and to read that people are inspired by my built. I'm deeply flattered. Keep building and biking!

<p>Just ordered a set of couplings. Let's see where this leads... ;-)</p><p>Thanks a lot for the inspiration!</p>
<p>Happy to hear that you're inspired! I'm curious what you'll do with it, so feel share a picture of your build. (but please don't cut the NSU in two ;) )</p>
<p>No need to worry! I have a beat down 70ties bike which I pulled out of a pile of trash that I want to turn into something funky.</p><p>You can follow the build thread here, if you want: http://www.tretharley.de/phpbb/viewtopic.php?f=49&amp;t=29473&amp;p=584529#p584529</p>
<p>I see you made the cuts already. I'll brush up on my German and follow the thread. Good luck with the build!</p>
<p>I will put up a picture here when I'm done!</p>
<p>Done!</p><p>The bike goes be the (obvious) name CAPITAN TERROR. It has some extra features like the cable for the gear shift can be separated as well. The shifting is done with the right break. The disc wheel will probably get it's own instructable, once I make another one. </p><p>Again thank's a lot for the inspiration. I lead me to build a very unique bike!</p>
<p>That turned out really cool! Well done! And I'm happy I could provide some inspiration. </p>
<p>Thanks again! I just give my ride <a href="https://www.instructables.com/id/Cover-a-Bike-Frame-With-Comics-or-Other-Paper/">it's own instructable</a>, mainly covering the decoupage part and made a reference to your instructable on the folding aspect of it. I hope you're ok with that.</p>
<p>A wonderful job, thanks for sharing !<br>I have one question however, what do you mean by the ability to separate the the gear shift cable ? Do you have a cable cut into two with some kind of connector to make each end fixed, or unfixed to the other ? How did you make that ? with your Rolhoff stuff, is it its purpose ? My german is not so good so I don't understand your thread in the forum, not either your rohloff order.<br>Thanks for your explanations.</p>
<p>You're on the right track. I cut the shifter cable in half at about the same location as the frame coupling and fixed the two ends together with the rohloff coupling (in reality I connected a break cable to a shifter cable, because I use the break lever as shifter, but that's a completely different storie...). Now you can twist on side of the coupling a quarter turn and the ends come apart. To get it, I recommend watching the video on the rohloff site a about 1:30min: http://www.rohloff.de/en/technology/workshop/videos/internal_gear_mech_cable_replacement/index.html</p>
<p>That`s a nice connector. I`m thinking of ordering it however it is not cheap.</p><p>I will need three of these connectors....</p><p>I found the video here: </p><p>http://www.rohloff.de/de/technik/werkstatt/montagevideos/zugverlegung_intern/index.html</p>
As good as this connectors are for shifter cables, I strongly advise against the use for breaking cables. The fixation of the cable inside the connector is enough for shifting gears, but the forces while breaking are much stronger and you might pull the cable out of the connector, which could end badly!<br>Probably you should adapt the kind of pull hook which is used for drum breaks.
So far, so good. I had never heard of a &quot;fixie&quot; until I saw your Instructable. I immediately went out to find a cheap bike, found it and cleaned it. I gave it new tyres and went for a test ride. <br>I immediately fell in love with it and I started to get some regret for the &quot;cutting plan&quot;. But I made my decision. <br>I really liked the shifters and gears, and obviously the brakes. <br>So I decided that I want to keep these functions. <br>So now I painted the bike with some paint I had as leftover because maybe some parts will have to move to keep in functioning. <br>I had an awful lot of work removing the original paint. Next time I'll keep it. <br>I have a lot of fun making this project. <br>Thanks for your inspiration and clear instructions. <br><br>
<p>Wow, that looks neat! I love how you did the headset lugs in a contrasting silver. Next time you can keep the original paint, or clean it and paint over it if it is not in a too bad shape. (Mine was, that's why I had to take it down to bare metal.)</p><p>I'm curious how the folding mechanism will work with the gears. And it seems your rear tire has very little clearance from the frame at the top, or is that just because it is all the way in the back position?</p><p>Thank you for sharing!</p>
As you can see, the job is still in progress. I was just enthousiast to mount some parts to get an idea of the looks and I wanted to share it with you, because you lightend up my enthusiasm. <br><br>My tyres are selected for comfort and these are the tires which my bike mechanic came up with. I also like them because of the safety reflection. In Holland traffic is - as you know - busy. <br><br>I'll keep you updated.
<p>I ordered this part for the shifter cable on my folding bike: </p><p><a href="https://www.bike-components.de/de/Rohloff/Bajonettverschluss-p18572/">https://www.bike-components.de/de/Rohloff/Bajonett...</a></p><p>I works really good (if you thighten the screws very hard)</p>
<p>Thank you very much. I know you ordere that part because i am following your&quot;captain Terror&quot; bicycle project on your tretharley.de website.</p><p>My shifter cables amazingly are positioned outside the frame and do not cause any problem when folding or reassembling the bike.</p><p>My rear brakecble is now mounted inside the frame, through the couplings. Till now it works but maybe i am going to use your bajonet coupling because the outside cable seems to suffer a lot from taking the parts apart each time.</p><p>I`ve been riding for a couple of hundreds kilometres now and experienced no problems with the couplings. Even one time i apparently forgot to tighten the screws an after after a few kilometres i noticed it because the bike felt a little wobbly. It did not feel unsafe at all, there is a good strength in the construction that prevents falling apart when using the bike.</p><p>I like it very much!</p>
Does it effect the frame at all? is it still stiff or does it flex more?
<p>There is no flex in the joints at all, so it is still as stiff as it was before 'surgery' :) Also, the way the joints are oriented (with the small pipes being horizontal), they help to counter torsion.</p>
<p>Amazing, i love it. dint' know that those copling exist.</p><p>I'm gonna try to make my own S&amp;S copling, because they're hell expensive.</p>
<p>any tips where i can find these or similar couplings online? they doesnt have them here.</p><p>also ... if you moved the place there you cut the bike forward and got a similar bike then you could possibly also build a side by side trike/tandem . bike lego!</p>
<p>Ha, I love the bike Lego idea! I was considering building an entire bike out of these clamps and tubes, but that gets rather heavy and also somewhat expensive.</p><p>You could try either http://www.keyclampstore.com or http://www.alvinkeyclamp.co.uk (not affiliated with either. The first one is a bit cheaper). </p>
<p>In both the joints, won't it be better to have them rotated 90 degrees? That way the (mostly downwards) bending force will not be coming on the hex bolts holding the 27mm tube to the swivel tees, as the axis of rotation of the swivel tees is in alignment with downwards bending.<br>If you turn it 90 degrees, the 27mm tube will be facing up-down instead of left-right and the downwards force will come on the structure rigidity of the tube instead of the hex bolts. Only the sideways frame movement will come on the hex bolts which isn't much in comparison to the downwards force. This way you'll have to align the 2 halves together in a straight line each time you assemble it, but you'll be sitting on a lot safer and sturdier joint.</p>
<p>You are right to a certain extent, as it would indeed be a bit stronger. Not by much though, as most of the bending force is negated by the triangular shape of the frame. The top tube is 'compressed' while the bottom tube is 'stretched'; neither is bent. That's why triangles are awesome! If it were a single tube, or two parallel tubes, it would indeed be a lot better to turn them 90 degrees and in my original design I drew them that way too. However, the triangular shape of the frame actually makes it impossible to set it up that way. To be able to take the two halves apart, the two 27mm tubes have to be perfectly parallel. Both coupling halves on either part have to slide onto and off the 27mm tubes in the same direction. You might be able to slide them on and off with some force, as there's is a bit of flex in the steel and the 27mm tubes are short, but the fit is already rather tight.<br><br>Not in an attempt to insult your intelligence (which would be futile anyway judging by your Instructables), but to make this understandable for everybody: hold you fingers in the shape of a L (mimicking non-parallel 27mm tubes) and slide a roll of scotch tape on either finger (mimicking the open end of the couplings). Now try to slide the two rolls off at the same time and in the same direction. You'll find that this doesn't work. Your fingers, as the tubes, need to be perfectly parallel to be able to slide the tape rolls on and off.</p>
<p>By the way, a solution would be to take out one of the 27mm tubes entirely when disassembling, but the fuss, having one extra bolt tightened by hand, and the risk of losing the small tube doesn't outweigh the minor gain in strength.</p>
<p>Ah I get it now. Pardon my ignorance in the force dynamics of a bicycle frame's tubes. I checked out the force diagram of a cycle frame and you're right that most of the force is stretching/compressing instead of bending, so the change won't be of much use, except making assembly difficult. Thanks for clarifying.</p>
<p>Clever! If you just want to fold the bike ad not carry in two separate halves cables aren't an issue. Just get slightly longer cables and have a multi-speed bike, with a rear brake. Would make transporting in some cases a bit harder, but I'd just use some Velcro straps to hold the two halves together and prevent pulling on the cables too much. Make the straps long enough to wrap around frame and form a carry handle. </p>
Very nice! Thanks for sharing.
<p>Interesting use of these couplings. I made a bike repair stand with them using galvanized pipe. I had to order the couplings online. What store has them in the 'furniture making aisle'?</p>
<p>In The Netherlands, all mayor hardwarestores have them. A bit overpriced maybe, but you don't need much for this project. If I was building something bigger, I'd probably order them online. Here for example: http://www.keyclampstore.com/key-clamp-fittings/27mm-key-clamp/</p>
<p>I couldn't find them anywhere but online. I'm pretty sure I bought them from the same supplier. They are a bit expensive because the shipping is high due to the weight.</p>
<p>Bike repair stand</p>
<p>Nicely built! I see you used the exact same coupling I used at the top.</p>
<p>Yes and that's what's unique about these particular couplings. Very flexible.</p>
<p>I love this 'ible and felt compelled to write about it! http://mesquitehugger.blogspot.com/2015/11/a-spark-in-quest-for-diy-folding-bike.html</p>
<p>Nice blog! And I love the 'some cool Euro bike dude' nickname! :D</p>
<p>sooooo no back brakes ?</p>
correct. aside from the brake cable getting in the way when breaking the bike down to travel, ~80% of your stopping power comes from the front brake. and if this is a fixed gear, the rear brake is even more irrelevant.
<p>Very clever and yet simple, hope I can find these couplings where I live.</p>
<p>In UK, they go under the brand name of Key Clamp.</p><p>Loads of uses from making up handrails to stuff like car ports (or bike racks)</p>
<p>For the rear, I'd use a back-pedal brake since you're going single speed anyway. Much more reliable in mud.</p>
<p>Very clever indeed. But to reply to your incorrect assertion that most foldable bikes are &quot;slow and boring&quot;, fixies with no brakes are &quot;illegal and dangerous&quot;. ;-)</p><p>Keep on biking !!</p>
BOSS idea and project!! Nicely explained instructable even though there are some questions I'll be inclined to ask when I attempt this myself. Bicycles are my main passion and I've never owned a fixie, nor a 'coupled' bike. I do, however, love singlespeeds and this is where I would hedge my efforts to. <br>Hat's off bro!
<p>I have been thinking about this and have concluded that using a 1/4&quot; bigger pipe would do the trick and would be even cheaper! I have a small car and my bike doesnt fit inside this is a great project for me.</p>
GENIUS!!!... BRILLIANT!!...
<p>Looks really nice :D How much does the bike flex? Been a fixie is a big issue, especially when you brake, because you put a lot of pressure on the frame.</p>
<p>The couplings are more rigid than the frame itself :) And it was quite a decent bike to start with, so flexing is limited. Some flex is noticeable in the fork when braking hard, but that's the same flex that smoothes out some bumps in the road so I'm actually happy with that.</p>
<p>I flew KLM to and from Amsterdam with a 20&quot; folding bike. No restrictions on the way there, but KLM broke my spider and chainring, then refused to compensate. On the way back i was forced to pay 100 euros &quot;excess baggage&quot; fee when--get this--the folded, covered bike was my only checked piece and weighed less than 20 kilos. So how did you avoid being clusterfucked in the same manner?</p>
<p>I'm sorry to hear that! Did you have to pay extra because of its size (LxWxH &gt; 158cm)? I do plan to take it on a plane but haven't had the opportunity yet, so I don't know what they will say. Fully disassembled, it stays within the weight limit easily, but the dimensions might be a problem. Though my experience is that how they handle exceptions differs quite a bit per airline.</p>
<p>if you wanted to get real fancy, and knew someone with the skills, you could braze the frame mounted halfs of the clamps on, and also probably the fixed portion of tube in the clamp. Then there'd be less risk of multiple bolts possibly working loose, though I imagine a little lock-tite could prevent this anyway.</p>

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