We didn’t clean the bike before starting. And you know what? We wish we had.

You’ll need quite a few tools for this one. 5, 6 and 8mm Allen keys, crank extractor, cassette lockring tool, chainwhip.

There are a number of ways to achieve the desired one-geared results ranging from the free to the spendy. We’re going for the middle ground here with a conversion kit from Forge. It’s £37 for all the bits you’ll need. We’ll point out the slightly bodgetastic but ofter free alternatives as we go along.

The very first job is to remove both derailleurs, shifters and associated cables. Just undo the obvious bolts and take them off. You can get the rear mech off the chain by taking out one of the jockey wheels, although we’ll be breaking the chain in a few minutes anyway. Then take the back wheel out and remove the cassette. We’ve covered this in a previous article if you don’t know how. Put the lockring to one side, you’ll need that. Once all that stuff’s gone, take a moment to heft it in your hands – your bike just got that much lighter…

The Forge kit includes a single Shimano sprocket intended for BMX. It fits on to the standard freehub splines but has deep teeth and no shifting ramps, ideal for our purposes. If you buy nothing else for your singlespeed project, buy one of these – they’re only three or four quid. It’s possible to use a sprocket out of a cassette but the shallow teeth and ramps can be troublesome unless your chainline’s exactly right. The kit also includes very smart aluminium spacers. You can get these from other companies too, or use loads of spacers out of old cassettes or some bits of PVC waste pipe cut down with a hacksaw.

Once your chosen spacers and sprockets are in place, use the cassette lockring to hold it all in place. The Forge kit aligns the sprocket with the middle chainring position. If you’ve got specific spacers generally the wider one goes on first, then the sprocket, then the other spacer. If you’re bodging, it’s easiest to aim for the middle position which should be 20mm in from the face of the locknut.

That’s the back end sorted. Now it’s time to remove redundant rings from the front. Refer to our chainring replacement article to find out how to take the drive-side crank off and remove all the chainrings. If you’ve got a chainset with the middle ring bolted on to the big ring and no spider or some other such nonsense you’ll have to get one of the spider replacements available or just leave a redundant chainring in place.

Assuming you’ve got a crank with a proper spider, your next step is to put one chainring back on. For off-road the “traditional” ratio is 2:1, so 32 front/16 rear, 36/18 and so on. Happily most middle rings are 32 teeth so the cheapest option is to reuse the existing middle ring. If you want or need to buy one, look for one with deep teeth and no shifting ramps. You’ll need shorter chainring bolts and collars (ask for single chainring bolts) although if you’ve got lots of washers hanging about you can bodge it. Fit the chainring in the middle ring position.

Put the crank back on. If you’ve left the chain in place offer it up around the chainring and sprocket. It’ll probably look something like this – without big chainrings and sprockets and a rear mech there’s loads too much. So it’s out with the trusty chain tool to split and rejoin the chain. Make it as short as you can without it pulling tight.

You’ll probably end up with something like this. If you’re really lucky you might find that your particular frame and chosen gear ratio magically give you just the right chain tension straight off. You’re looking for about 10mm vertical displacement in the top run of chain. Looser than that and the chain’s likely to fall off, tighter and the cumulative tolerances in the runout on the sprocket and chainring, alignment of BB axle, runout on the spider relative to the crank and so on are likely to give you intermittent tight spots as you pedal. Most bikes will need some help to attain the ideal tension.

The low-rent solution is to just use the old rear mech, using the limit screws to keep it in line (or find an old gear cable, feed it into the mech until the nipple that’s usually in the shifter sits in the barrel adjuster, clamp the cable, cut off the excess and use the barrel adjuster to move the mech in and out until it lines up) and shortening the chain so the cage is pulled right forwards. It works, but it’s not that elegant. Forge’s tensioner is a super-simple pulley on an arm – screw it to the derailleur hanger, tilt it to tension the chain and snug up the bolt.

Experiment with the tensioner pushing down (as above) or up (as right) on the chain. Up means that more teeth are engaged but you may find that one way runs quieter or only one way will work due to the shape of your frame or something. Forge also do a tensioner with a jockey wheel instead of the roller which will be slightly quieter than this one. There are several other devices available, including the Singulator which is spring-loaded and adjustable in and out.