How to Make a Fixed-Gear Bike in 7 Easy Steps
There’s a reason why single-speed and fixed-gear bikes have become so ubiquitous. For commuters who rough up their rides, the simplicity of a single-speed makes it tremendously easy to clean and service without extensive bike knowledge.
But besides the logistical ease, there’s also something special about a bike with one gear—it just feels freeing (unless you’re trying to conquer a giant hill). That intimate connection between rider and road makes a person fall in love. As the late Sheldon "Coasting Is Bad For You" Brown wrote, "There is an almost mystical connection between a fixed-gear cyclist and bicycle: it feels like an extension of your body."
If you have an older bike you want to make fixed-gear, here’s how to do it.
Remove your rear wheel and look at the dropouts—the slot where the rear axle goes. If the dropouts are horizontal or diagonal, you’re good to go. If they’re vertical, you could make it work, but it’d be better to go with a different frame.
Measure between the dropouts. Most old frames have a dropout spacing of around 126 millimeters. If it's more, that could be an issue if you're using a standard fixed-gear wheel. You can resolve this by cold-setting (bending) the steel dropouts closer together—a double-black diamond move you probably shouldn't try—or simply replacing your hub with one a wider one.
If you already have a wheel made for single-speed or fixed-gear riding, it'll have a spacing of 120 millimeters. Older frames with horizontal dropouts usually have a 126-millimeter spacing so there's going to be six millimeters you're going to have to make up for (which you do with spacers between the cog and locknut).
I have a common flip-flop hub (both coasting and non-coasting cogs) so I tried a spacer on each side at first. Unfortunately, when I tested the wheel in the frame, the wheel was too far left, so I put both spacers on the coasting side and things lined up. You might have to experiment, and it's important to remember to put the spacers right up next to the cog, between the two nuts that touch the frame.
If nothing works or you don't have a long enough axle, you'll have to replace it or redish your wheel. Both are double-black diamond moves best left for a seasoned mechanic.
You could also re-use your old wheel with all the gears, but it's pretty complicated and you can find cheaper wheels pretty easily. If you want to know more about that, check out Sheldon Brown's essential notes.
If you don't want to ride with impossible gearing, you're going to want to do something about that enormous chainring in the front. You could keep the 50 or 52-tooth behemoth, but it's nicer to put something a little smaller on. I found a cheap 48-tooth ring for my relatively-flat commute and swapped them out. If the rings won't come off with just an allen key, you can use a quarter held in place by a pair of vice grips to grip the nut from the other side so the bolt unscrews.
Pro-tip: You can also use this time to ditch the small ring. It's only weighing you down.
Remove all the unnecessary shifting hardware from your bike. Derailleurs, shifters, cables—they all can go. Get that weight off the bike and off your mind.
Since you've changed your front gearing and removed your derailleur, your chain will be far too long. Use a chaintool to shorten it. You want to be able to push the bike back in the dropouts and have your chain pretty taught, so don't leave it too loose.