HOW TO SINGLE SPEED…
There are several methods of achieving a singlespeed bike. Many of the strange components needed won’t be found in your local bike shop as demand for these items is pretty low. However you can buy almost everything you need from me.
BUY A BIKE… simply buy a singlespeed bike, or a frame with horizontal dropouts. These dropouts allow you to pull the rear wheel back in the frame to achieve chain tension. I strongly recommend the use of a device like the Surly Tuggnut to ensure your rear axle does not slip in the dropout when you stomp on the pedals. The Surly device not only allows you to tune for perfect chain tension, it also opens beer.
CONVERT A REGULAR BIKE using a tensioner… Take off all the geared rubbish, and pop on a chain tensioner. These are like tiny rear mechs that take up the chain slack. Some have a jockey wheel and hang down like a mech - others use a roller and push the chain up, these are better if you ride rocky and rooty trails where mechs get mashed.
You can also use the blooming clever White Industries Eccentric Eno Hub, the bolts that mount the hub to the dropouts are not in the centre of the hub, they are offset by around 7mm, simply rotate the hub to get tension, then lock down the allen bolts. I have used one of these for several years on an offroad cross bike and it has worked very well, both as a singlespeed and as fixed wheel bike. You can buy these from me for £125.
You will also need to set up the rear wheel with one cog. You could buy a singlespeed specific rear wheel and use a screw on BMX style freewheel. An OK alternative is to take the geared cassette off the rear wheel and replace it with a single cog and some spacers. These can be purchased , or you could use the spacers from between the cogs on a few old cassettes.
When you strip down your chainset to one ring, you will no doubt find that the bolts that held two rings in place are too long to clamp down a single ring – but don’t panic, skinny bolts are available in the shop.
GETTING LUCKY: Everyone likes getting lucky... many beers have been consumed.. it's the end of the night and you're standards have never been lower and despite the stains, you're still attractive.... STOP, we're taking a different kind of lucky...
You may not need a chain tensioner, the distance between your drop outs and your bottom bracket may be spot on, and therefore allow you to run just a chain, a chainring and a rear cog… and get perfect tension. You can help yourself to get lucky, by playing around with the size of your cog and ring. For every tooth you remove will reduce the effective bottom bracket to rear axle length by 1/8 of an inch. So you take up the slack by using a bigger cog or ring and create slack by using a smaller cog.
There is a brilliant and super rare component called a half link. This is a single chain link that goes from wide to narrow within one link. Using this will make your chain half a link shorter or longer, equating to a 1/4 inch change in you effective bottom bracket to rear axle distance. Simply use a combination of these two techniques to get good chain tension. IMPORTANT BIT: Chains stretch when used, so your chain will get slacker. You should check the tension regularly and adjust your ring/cog sizes, remove/add a half link, or replace the chain to maintain tension.
THE PRINCIPLES OF SINGLE SPEEDING
WHAT GEAR? Standard singlespeed offroad gearing is 32 teeth at the front and 16 at the rear, AKA 32:16. This gives you a 2:1 ratio. Any other 2:1 ratio will feel the same such as 36:18 or 42:21. However if you live somewhere particularly steep use a slightly easier gear such as 32:17 or 32:18. On the road on a 700c wheel any big gear goes – I found 48:16 hard work, and 42:16 about right.
BIG TEETH: Just like Janet Street-Porter, jolly big teeth are a recipe for success. Both your front chainring and rear cog should have full size tall teeth. Many geary teeth are cut down to allow easier shifting of gears – you want your chain to stay on, not jump off (nasty violent and maiming injuries may follow).
CHAIN TENSION: The secret to a good reliable single speed is good chain
tension. A slack chain will cause you chain to skip off, often with hideous consequences (I have scars). A Surly Tuggnut or Spot Rocket tensioner prevents this by allowing you to fine tune the tension (it also allows you open bottles of beer)
CHAINLINE: When setting your bike up you should try to get the chainline as straight as possible. The chainline is the route your chain takes from the cog to the chainring. Get down on your knees and squint up close at the chain - looking along the bike. You want to get it as straight as possible by either moving your rear cog about (by playing around with the spacers if you are using an adapted hub), moving the front ring to the other side of your crank, or using a bottom bracket that's narrower or wider. Trial and error, you may get lucky first time.
VERY IMPORTANT BIT: All bloody hell will break loose when your chain skips off the ring. This always happens when you are mid sprint. All the resistance that you are pushing against with your entire body will suddenly disappear. You will throw your face at the ground, your bike over your shoulder, and your gentleman’s regions will always head straight for something sharp and metallic. Use tall teeth, check the chain tension, make sure everything is clamped down tight and wont slip, and you will live a long and frisky life.
DONT FORGET ITS FUN: Beyond the above I would also say you should always wear a lid, have fun, do big (environmentally sound) skids, don’t take any crap from motorists, and stop at a pub towards the end of your ride to replace lost carbohydrates.