Nuts ‘n’ Bolts – Ten Dollar Fixed Gear Conversion

[[image:fix_mini.jpg::inline:1]]I know that what I am about to discuss here will raise some purist hackles, but for those who have a UBBTS (Universal Bike Boom Ten Speed) and want a quick, dirty, and cheap fixie conversion, read on.

Published October 22, 2007 by C.I.C.L.E.
By Harv :: Photos: Harv and Alice

[[image:fix1.jpg::inline:1]]Another popular theme at the Bike Oven is the request for a fixed-gear conversion. Preferably at a very low cost. I know that what I am about to discuss here will raise some purist hackles, but for those who have a UBBTS (Universal Bike Boom Ten Speed) and want a quick, dirty, and cheap fixie conversion, read on. If your rear wheel drop-outs are more or less horizontal, you can easily do the conversion. You need to be able to move the wheel horizontally in the dropouts to adjust the chain tension.

Basically, you just remove the derailleurs and the freewheel and install a track cog and a lock ring onto the hub. You then remove one of the chain rings and run the remaining ring in the inner position on the crank to get a decent chain line. If you can score an old bottom bracket lock ring from a junk bike, you can get away with about a 10 or 15 dollar cash outlay. Whenever a cartridge bottom bracket is used to replace an old cup, spindle and ball type, there is a lock ring left over with the removed parts. So your Local Bike Shop should be sweeping them up off the floor and tossing them in the trash. Track cogs in a range of sizes from 13 to 18 teeth are available from bikepartsusa.com for about $10 plus shipping. Be sure to get the 3/32 cog so that you can use your original chain and chain ring.

Remove the rear wheel, then remove the original freewheel. At the Bike Oven we clamp the freewheel remover tool (after retaining with axle nut or skewer) in the bench vise and then turn the wheel counter clockwise to break the freewheel free. Then thread on the track cog, tightening it all the way by hand or with a chain whip, The bottom bracket lock ring follows next. Tighten the lock ring against the cog with a lock ring tool and a chain whip or "Monster Cog Wrench" described in a previous Nuts 'n' Bolts. For extra security if you are NOT going to retain both brakes, apply some Locktite thread locking compound. But I recommend that you retain at least the front brake. I also recommend you go to a nutted solid axle if your rear axle is the hollow quick release skewer type. Kits with a solid axle, cones, lock nuts and 15mm axle nuts are available for a few dollars.

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Select the chain ring that will give you the gearing you prefer. Place it (if not already there) at the inner position on the crank spider. The chain line can be moved inward by reversing the crank spindle if it is the loose type (not cartridge). Crank spindles are usually asymmetrical because of the two or three chainrings which must be accommodated on the drive side. Reversing will tighten up the drive side chain line, bringing the single ring inward. Further tweaking of the chain line can be done by spacing out the chainring or changing the bottom bracket spindle size.

For chain ring bolt spacers you can use standard 3/8 inch lock washers after tightly clamping them in a vise to flatten them out as much as possible. I prefer these methods over changing rear axle position and re-dishing the wheel. This way, you can easily revert to the original multi-speed configuration if you decide that fixed gear riding is not for you. And you don't have to mess with re-dishing an old wheel which may have seized spoke threads and may require different length spokes.

All that is left is to shorten your chain to fit the new setup. Allow for some adjustment. Rotate the crank slowly, find the tightest position of the chain and adjust for about a half inch of total up and down movement of the chain. Too loose and the chain may come off, too tight and you may bind or break the chain. After tensioning the chain, turn the crank slowly (watch your fingers, don't pinch them between the chain and a sprocket) and check the chain tracking over the cog. If the chain tends to climb the cog teeth and you hear a clicking noise, stop – you have an alignment problem. This could be the wheel not straight in the frame, a bent frame, or a chain line problem. Don't continue until you resolve this situation. Ride around and recheck the chain tension. If the range of adjustment is insufficient to allow proper chain tensioning, you may need to add a half-link (also called an offset link) into the chain, either with or without a master link.

If your bike does not have horizontal dropouts, you can gain some chain adjustment capability by slotting out the existing dropouts with a rat tail file. Slot them out horizontally toward the rear of the bike. It does not take much, an eighth of an inch would do quite a bit of adjusting if you get the chain length as close as you can by trimming off links and using the half-link trick if necessary.

Another tip on adjusting chain tension on a fixie, a single speed, or a hub-geared bike: Hand tighten the nuts just enough so that the axle does not slip loosely in the dropouts. Pull the wheel back until you get the desired tension in the chain. Incrementally and alternately, tighten the axle nuts by pulling the wrench on the drive side nut starting at the 4 o'clock position of the wrench and ending no farther than the 8 o'clock position. Then pull the wrench on the non-drive side nut starting at the 10 o'clock position and ending no farther than the 2 o'clock position. What this will do for you is keep a rearward force on the axle and prevent the chain from pulling the axle forward and upsetting the critical tension you have so carefully set.

A brief foray in bicycle engineering might be apropos here. Ideally, the rear axle will be clamped in the frame at the point where the chainstay and seatstay axes intersect. Otherwise there would exist a bending moment tending to whip the rear frame triangle to one side and giving the rear wheel some steering input when pedaling hard. So try to keep this from happening by not allowing the axis of the rear axle to drift too far off the ideal position.

The above will give you an idea of whether fixed gear riding is for you. If it is, you may want to upgrade your rear wheel to a track wheel and your crank to a track crank, or a BMX crank if you want to save some money. If you go this route, you can change to 1/8 chain and 1/8 inch wide cog and chain wheel. Good prices on BMX cranks, chain rings, and solid axle kits can be had from niagaracycle.com

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