Why Single Speed? A combination of 'luck' and timing have led me to re-rig my commuter bike as a single speed. The 'luck' part was a pulley on my circa 1995 rear derailleur exploding. The timing part is the rise of single speeds in general. I've been noticing the rise in single speeds in the last couple of years as a bike commuter. They look so....simple and maintenance free!
I'm riding a 14 year old Kona Kula, once my singletrack steed, now my urban commuting stalwart. The key thing about converting a bike with vertical dropouts into a single speed is that you can't slide the rear wheel back and forth to get the perfect chain tension. You need a chain tensioner. A chain tensioner is like a derraileur-lite that pulls the chain taut. There are several brands out there, all of which make a simple, bullet proof device.
The other key thing about converting a standard bike into a singlespeed is what to do with your rear cluster. There are a number of freehub to singlespeed conversion kits out there that provide spacers and cogs to replace your freewheel.
I ended up choosing the Forte Singlespeed conversion kit, made by the Performance Bicycle house brand. This was the only brand I found out there that offered the freehub spacers and cogs, as well as the chain tensioner, for by far the cheapest price -- for $25 I got everything, including 3 cogs to experiment with. Compare that to the Surly solution, which was going to cost $50 for the chain tensioner, and $30 for the spacers, and $10+ for the cog.
It also had what I considered to be a key feature: it allowed me to adjust the horizontal placement of the tensioner. This was important because I had no idea where I would be placing the cog to line up with the chainring.
I also wanted to try using an original cog and chainring, since I had replaced them a year ago and they weren't completely beat down yet. The preferred way to go is to do a clean replacement, but that would require a new chain and front chainring, and I wasn't sure that I could find a replacement front chainring without a special order.
Installation was easy, and gave me a chance to clean my bike for the first time in 6 years!
- a cassette removal tool and chainwhip for freewheel removal.
- an allen wrench for the usual.
- a crank puller to remove the inner chainring on the triple.
- a chain tool to break and resize the chain.
This is where the horizontal adjustablilty of the Forte chain tensioner became really useful. It let me slide the tensioner cog over to the outside with an allen wrench.
Step 2: remove the freewheel using the chainwhip and the freewheel tool.
Step 3: install the chain tensioner where the real derailleur used to be.
Step 4: position the singlespeed cog -- using spacers to fill up the freehub around that cog -- and the chain tensioner cog so that they are inline with the chainring. This is important. If you don't line things up, the chain will derail. In the picture below, note the spacers around the cog. Because I installed my chainring on the outermost position, I've had to position the cog at the outer end of the freehub (with only one spacer between it and the cassette lockring).
Step 5: whip out the chain tool resize the chain so that the chain tensioner is engaged (i.e. it has tension).
I used a 16 tooth cog from my old freewheel, and my existing chain. This may not work because that cog was designed to be 'shiftable', and the ramps on the cog body may derail the chain. However, I wanted to give this a try before buying a new chain and front chainring.