How to do a Singlespeed Conversion

For about a year I've been wondering what the attraction to singlespeed was. Why would anybody want to remove their gears and have to resign to one ratio that probably wouldn't ever be optimum? What's the appeal in being neither ever able to go up hills or fast on the flats?

Well after reading a few forum posts in mtbr.com and some content from Sheldon Brown, I could see the answers clearly:

1. Simplicity. There's a lot to be said for 'keeping it simple'. It's elegant, clean, and not much can go wrong.
2. Speed. Yep, speed. All the singlespeeders I ever rode with blasted past me. I could never catch them and I wanted to find out why.
3. And the most obvious one, weight.

 Conversion kit, including cog and lockring

So I took a trip to Fab's Cycle (Singapore) and picked up a singlespeed kit. This is simply some aluminum rings (in a variety of sizes), a lockring and a cog. The one I got was 18t.

You will probably also need a chain tensioner, as your rear derailleur will be removed, you'll need something to keep the chain taut and from falling off.

I couldn't find one when I did my conversion initially.

Step 1: Remove lockring
To do this you will need a chain whip and a cassette lockring tool, along with a wrench.

Goodbye cassette, we won't ever need you again.

It may be tight, but crank the wrench counterclockwise with your other hand on the chainwhip to prevent the cassette from spinning. The lockring will come off.

Step 2: Pull the cassette off
Now here's where I ran into my first problem: The cassette's cogs had dug into my soft aluminum freehub body, gouging itself in. I had to rally yank on the cassette to get it off.

Step 3: Put the spacers and cog on
Once the cog cassette is off, all you have to do is slip a few spacers on and then add the cog. But those grooves in the freehub body prevented me from sliding the cog on.

Cassette partly off.
Notice how the three biggest cogs are all connected. 

Cassette off.
Notice the grooves in the freehub body.

 

The cog wouldn't fit!

...and it slid right on.

A bit of filing...

Tightening the new lockring.

And the final result.

Somewhere along the way you have to remove your front and rear derailleurs, and maybe front chainrings (unless you're already on 1x9 or 10).

It's obvious from the image above that the chain is too loose. If you are lucky and your chainstay is just the right length, and you have chosen the right cog sizes, your chain may fit perfectly. But finding this 'magic gear' is hard.

There are a few solutions to this - get a tensioner, buy an eccentric bottom bracket, or get a frame with horizontal droupouts (ha!). I chose the first.

With the tensioner.