It all starts here — whether you want to convert your single-speed to a fixed-gear or add a new gear ratio to your current fixie — pick a cog to suit your needs and abilities.
The less teeth a cog has the higher the gear ratio — harder to pedal, faster. Odd numbers of teeth (esp primes) give you more skid patches & help tires last longer. 17t is a popular, balanced choice.
Flip your bike over onto the handlebars/seat or throw it on a repair stand so it is easy to work with.
Nearly all track hubs are threaded on both sides so you can have two cogs handy on one wheel. This bike already has a freewheel — we'll add a fixed cog so it has both single-speed & fixed options.
Grab your 15mm hex wrench…
…loosen the rear wheel nuts and remove the rear wheel from the bike.
If you haven't already opened a cold one, now's a good time. This is a hard step to miss because all bike tools have bottle openers integrated into them in one way or another.
Scrub down the threads on your hub so they clean are shiny - like new. You don't want any stray bits of dirt f#€&ing up your precious hub threads. Seriously. Get that s*!t clean.
While you are at it, give the whole wheel a good scrub down. Microfiber cloth works wonders on getting grease and grime off.
Hell, just give the whole bike a proper wash & detail. Fixies are at least 50% fashion. What's the point if your ride's not looking tight?
Time to add the new cog & lockring. One side of the cog (shown here) is made to fit flush with the lockring. The other side faces the spokes & has a spacer to help line the chain with the crank.
Apply a liberal amount of grease to the theads of the cog and the lockring…
…and add a nice coat of grease to the hub threads as well. You want everything to go on smooth while providing a good seal to water & grime.
Time to add the cog. Start by screwing the cog onto the hub by hand. Righty tighty. Smooth & easy. Never force it. If something jams, stop and inspect. Better to seek help here than dethread your hub.
Using a chain whip, tighten the cog firmly onto the hub. No excessive force, just nice & tight.
Start the lockring onto the smaller set of threads by hand as well. It screws in the opposite direction — lefty tighty.
Tighten the lockring with a matching tool. Most look like this and work with a variety of notch patterns. Check with your local bike shop if you're not sure which tool works with your ring.
Put the rear wheel back on, this time so that the new cog lines up with the chain.
Slide the rear axle back in the dropouts until your chain is nice and tight. If your new cog is significantly larger or smaller than your old cog you may need to adjust your chain size first.
Go find some friends & learn some fixie tricks! Enjoy your new set-up and ride safe.