This article first appeared in Issue #1 of Single Speed Outlaw way back in 2001. There's been a few updates in products and technology since then so the article has been updated here to reflect that. Surely hundreds (if not thousands) of eager beavers have used these simple instructions to enter the world of single speed mountain biking. If you've been thinking of giving it a try yourself there's no time like the present. Break out the tool set, grab a beer and get to it!
Here it is, the mandatory "How to build a Single Speed for Dummies" article.
If you're not a dummy, read on anyway, you might not be as smart as you think.
If you want to make a fixed gear the process is nearly the same but you can not use a chain tensioner to pick up your chain slack. It will cause bad things to happen. Go to
Sheldon Brown's web site, he's got the fixed gear conversion process covered. And he has plenty of other good bike info that's worth a stop by.
Scrounge up a bike. No, don't steal it. Bad karma will come your way in the form
of rabid bikers hunting you down and beating you with old seat posts. We're going to
assume you are starting with an already assembled geared bike. Sorry, but this isn't
"Bike Assembly for Dummies". A frame with horizontal dropouts is best, but not mandatory.
Remove the shifters, derailleurs and their cables. Build a small fire. Burn these
parts. (You might want to wait on the rear derailleur).
Figure out what gear ratio you want to run. MTB - For 26" wheeled bikes, try starting with 2:1 (i.e. the front ring has twice as many teeth as the rear cog, such as a 32 up front, 16 in the rear). This works out to 52 gear inches (see this calculator to make your life easy). For 29er (700c) wheeled mountain bikes, add two teeth in the rear (32x18 instead of 32x16) to approximate a similar gear. Road - try something like a 2.8:1 (42/15) or 2.47:1 (42/17). If you've got parts laying around, use them first to experiment. They're free and you might be changing things depending on your terrain. I usually settle on a gear that I can barely turn up the hardest hills I ride.
Remove the extra chainrings from the crank. You only need one, so pick the one that
fits with your decision in #3. Get some BMX style chainring bolts (made for single rings) or use some spacers
with the ones you've got so everything fits together nice. Try the ring in the middle
position. You want a straight chain line when you are done messing with the back wheel.
Remove the rear wheel. Cassette - go to 5.a.Freewheel - go to 5.b.
Remove the cassette. Bust it apart to get the cogs and spacers. Save the lock ring.
Pick the appropriate cog for the decision you made in #3 (tip: cassette cogs are made to shift, you can use one in a pinch but you'll be better off with a non-ramped cog made for single speeding. Surly, Endless, Shimano and others make versions from steel to aluminum, cheap to expensive). Find some more spacers. If you don't have any, take your local bike shop guy a pizza or beer and ask him if he has any junk
cassettes you can cannibalize. Or, get a piece of PVC pipe that fits exactly over the
freehub body and cut to length as needed. Space the cog on the free hub so you have a
straight chain line with the front ring (You can eyeball it but a straight edge is much better). Put the lock ring on and reinstall the wheel.
Assuming this is a multi-geared freewheel, remove the freewheel. If not multi-geared,
what are you doing reading this - you probably already have a SS. Go to the LBS and get
a BMX freewheel in the size you decided on in #3. Thread this on and reinstall the wheel.
Shorten your chain. Horizontal drops - go to 6.a.Vertical drops - go to 6.b.
Double check the chain line, snug the wheel up so you have tension on the chain without
binding and tighten the rear wheel. Adjust your brakes if necessary.
You've got a little more work pal. If you are lucky, you can remove some links and the
chain will fit nice and snug (this is known as the "magic gear"). Hate to break it to you, but it probably won't, so here's
what you do. Shorten the chain as much as you can. Try installing a half-link, many times you can get a gear combo to work with this little device. If this doesn't work, you'll need a chain tensioning device
to pick up the slack and keep the chain on track.
Option 1:Surly, DMR, Soulcraft and Rennen and
Paul' all make single speed chain tensioners for these conversions.
Option 2: You can use that rear
derailleur you took off in #2 (didn't burn it yet did you?) and play with the adjustment
screws to get things aligned.
Option 3: Do it yourself - head over to the
Dragon Tongue SS page
for some instructions on building your own.
Option 4: Get an eccentric axle for your hub from Fixed Innovations. This will allow you to adjust chain tension with a vertical dropout.
Option 5: Build a new rear wheel using a White Industries ENO eccentric hub. This is the cleanest but most expensive option but it will allow you to adjust chain tension with a vertical dropout. Even without the eccentric axle feature, the White Industries hubs are a nice component for the money.
Get the chain tensioned, check the chain line and tighten the wheel.
Take it for a test ride. Readjust.
Have a beer. Go on another ride. Think about what little maintenance this bike will be.
Repeat #8 as necessary.
The rule of 4:If you get your bike to work without any type of tensioning device (either the "magic gear" or with a half-link), you can use the rule of 4 to change gearing. This means if you change your gear combo by a total of 4 teeth you should still be able to use the magic gear or half-link successfully. For example, if a 34x18 gear works, you should be able to use a 36x20 or a 32x16 with the same set up.
Magic Gear calculator: Use the Fix Me Up gear calculator to find a gear that will work without a chain tensioner on your vertical dropout bike.