Singlespeed Conversion - Linux for Bikes

Singlespeed bikes are like Linux.

Eh?

A bit of background: I'm an IT administrator in my day job. I generally work with the usual suspects, Windows and MacOS. But being the geek that I am, when I want to try something different, I load Linux. Or, perhaps I'm working with an older and slower computer that I want to repurpose, again, Linux. Linux can be free, or if buying some prebuilt boxes, it can be quite expensive.

Sounds alot like singlespeed bikes right? Want to try something different than your geared bikes? Have an older bike that you want to fix but don't want to put much money into? What are the really cool kids riding

 these days? Singlespeed!

Specialized Stumpjumper Comp FS Singlespeed Conversion

Singlespeed conversion projects can range anywhere from free, to very expensive. I opted to keep my project as low cost as possible. My total conversion came out to just over $60. Here is a list of steps I went through to convert my Stumpy.

Tools:

chain whip

Shimano cassette lockring tool

chain tool

various allen wrenches

wire cutters

crank puller

Parts:

Performance Forte Team Brake Levers $14

Performance Forte grips $4

Performance Forte singlespeed conversion kit $25

SRAM singlespeed chain $11

brake cable and housing $4

short chainring bolts $5

I bought most of my parts from Performance.com using coupons and buying stuff on sale. The short chainring bolts I purchased from my LBS.

Determining your gear ratio:

Before disassembling anything, you will want to determine the gear ratio that you will be using. I didn't use any charts or fancy calculations. Instead, using my 32 tooth middle ring up front, I rode around and shifted around until I found a rear cog size that worked all around. In my case, I chose to go with the 16 tooth rear cog. Once you take your bike apart, you won't be able to do this so plan accordingly.

Once this step is done, you're free to start the disassembly of your bike. You'll likely be removing all of the cables, derailleurs, shifters, cassette, grips, and possibly barends. Since my cassette, derailleurs, and shifters are in great shape, I'll be using them on another project.

Crank:

My Stumpy came with the older style square taper bottom bracket. After loosening the bolts, I used my trusty crank puller to extract the cranks. After removing the inner and outer chainring, I reassembled the crank using the short chainring bolts. If you're really strapped for cash, you could grind the bolts 1-2mm. I opted to mount the chainring on the inner position, but depending on what type of hub you are using, you might have to mount the chainring on the outer side. After assembly, I reattached the crank to the bottom bracket.

Rear Hub:

In an ideal world, I would rebuild my rear wheel using a dedicated singlespeed hub, but since my existing wheels are still in great shape, I opted to use a Forté singlespeed conversion kit for use on Shimano hubs. The kit consists of various spacers, 3 cogs (16, 18, and 20 tooth), a locknut, and a chain tensioner.

Build quality seems pretty good, although I wish the package came with a greater variety of spacer sizes instead a whole bunch of small ones.

Using your freehub tool and chain whip, unlock and remove the old cassette from your rear hub. Now would be a good time to inspect and clean it.

Using the spacers, you will want to line up the selected cog so that it is in line with the front chainring. In my case this turned out to be about 2/3rd down the freehub.

Next you'll be installing the chain tensioner in the derailleur hanger. The Forté kit includes a way to adjust the horizontal position of the pulley.

The Chain:

Originally I reused the same Shimano 8 speed chain on the Stumpy conversion. Although I'm getting a bit ahead of myself here, I found that due to either improper chain length or wear in the chain, I was experiencing chain skip under high load. Rather than continue to fiddle with the existing chain, I opted to go with a brand new SRAM singlespeed chain. Your bike will be different than mine, but you'll want to get the chain as short as possible while at the same time allowing you to detach the rear wheel. As you can see from the picture at right, I was able to get the chain pretty tight, with the chain 

tensioner taking up the rest of the slack. In addition, I wanted to make sure that the chain wrapped around the rear cog enough so that a third of the teeth were being engaged. Incidentally, I have seen other bikes where the chain is parallel top to bottom. Mine was originally so, but as previously mentioned, I was experiencing chain skip.

Chainline:

After your drive train is assembled, you'll want to make one final check to see that your chain line is straight. If necessary, you may have to move the chainring to the outside, or move spacers in order to keep the chain line straight. You may also need to adjust the horizontal spacer on the chain tensioner as well. Remember, one of the advantages to riding singlespeed is the fact that your drivetrain is simple and efficient. If the chain is not straight, you'll cause premature wear and add unnecessary friction.

Brake Levers:

Originally I was going to use an old pair of Suntour brake levers to replace the old combination shifter/brake levers. I found out quickly that the Suntour units were not made to actuate V-type brakes (i.e. they don't pull enough cable). If I braked, I would end up hitting the grip with the levers. Once again I turned to Performance for a set of Forté Team levers. These are made to work with V-brakes and in my opinion, are constructed pretty well. All in all, they feel like my old XT levers, with just a slightly higher spring tension.

Conclusion

I must confess that when I first rode this post conversion, I suffered from phantom shifting syndrome. Coming from a 24 speed bike to a singlespeed is weird! The bike rides great, the drivetrain is much smoother. It's also alot lighter too.

So what's next for the Stumpy? Unlike the singlespeed purists out there, I won't be putting on a rigid fork. I did get a hold of a used Manitou Black fork though. I'll be putting this on in the coming weeks. In the meantime, I leave you with various links that I used for my research.

-Shel

http://www.sheldonbrown.com/singlespeed.html  (I just happen to have the same first name! Great reference)

http://www.cyclofiend.com/ssg/ (good reference photos)

http://forums.mtbr.com/forumdisplay.php?f=46 (you'll have to dig, but there's lots of good info)