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What is the best way to convert a freewheel bicycle to a fixed gear? |
What is the best way to convert a freewheel bicycle to a fixed gear? If your bike has horizontal dropouts (1-2" long-ish horizontal/diagonal slots in the back of the frame that the rear wheel hub is mounted on), you basically just need to remove the front and rear derailleurs, shifters, cables, and your brakes (if you're feeling particularly bold) and purchase /build a rear wheel with a hub that supports a fixed cog. A wheel with a 32 hole hub is advisable to ensure durability. You may also need to replace your chainring (cog mounted next to your pedals), chain, and bottom bracket (the spinning axle upon which your pedals are mounted) in order to yield a comfortable gear ratio for your riding situation and ensure that your chainline is as straight as possible. When purchasing a cog, there are two things to keep in mind: the width of its teeth, and the gear ratio you want to ride. With regards to width, it's important to consider that most freewheel bikes use a 3/32" wide chain and chainring. You can buy a fixed cog in this width to match your original drivetrain, but some folks prefer the added strength of a 1/8" chain (generally available from BMX shops). In this case, you'll need to buy a 1/8" wide chainring, chain, and cog. Make sure you also purchase a lockring to fasten your cog to your new wheel! As far as gear ratios go, a 48 tooth chainring and a 16 tooth rear cog (3/1) seem to be standard for fixed gear bikes, but you may want to pick something with a less reducible ratio (i.e. 48/15 = 16/5) because this will distribute wear across your rear tire more evenly if you rely on skid-stops to brake. In general, the more teeth your chainring has and the fewer teeth your cog has, the more torque you will need to supply to turn the wheel. I ride a 41/15 in a moderately hilly city (washington, dc) and i find it to be a pretty balanced experience. When you attach your new chainring, you may find that the bolts that held your old drivetrain together (and which were probably mounted through two or three rings of various sizes) are too long to allow you to fasten the single chainring snugly against the star shaped mount on your pedal crank. If this is the case, you'll either need to use washers to close the gap or buy "short stack bolts" that are specially designed for a single chainring setup. Attaching the fixed cog is pretty easy; it threads onto the inside threads of your fixed hub CLOCKWISE (tightens to the right). The accompanying lockring tightens COUNTER-CLOCKWISE onto the outside threads and keeps your cog securely in place while you ride. Note that some fixed gear hubs have threads for a fixed cog on one side and a freewheel on the other or threads for two fixed cogs.. make sure you screw the cog onto the right threads! Chainline is a third matter important to the construction of a durable fixie. Once you've got your new chainring and cog attached, mount your new back wheel by sliding into the horizontal dropouts and yanking it far enough back that the chain is taut (i.e. you can only move it about 1/2" by applying pressure with your thumb) and tighten the bolts that hold the wheel in place. Be sure to keep the wheel straight (you can usually eyeball this pretty effectively) in the dropouts. Once the wheel is attached , stare down the chain from behind the rear cog ... does the cog line up with the chainring? If the chainline is pretty straight (within 1-2mm) you're probably OK.. If not, you may need to replace your bottom bracket with a shorter or longer part to better align the chainring and rear cog. This all may sound a bit overwhelming, but it's basically just a matter of trial, error, and tweaking until you feel like everything is aligned and running smoothly. Be extra careful throughout the process to keep your fingers away from the rear cog while the the wheel is turning.. you can easily crush your digits between the chain and cog if your hand slips! Source(s): sheldon brown's site, old bike repair manuals, a lot of trial and error the question is why? you have to get rid of hundreds of dollars worth of components and then buy hundreds of dollars worth of components . when you can spend the same amount or less and get a bike that is fixed gear brand new with out having a bike mechanic do the work. cross trainer bikes are mountain bikes that are fixed gear and they are less money because they don't have many components that is the way you might wanna go. One of the biggest things you have to consider is if your frame has vertical or horizontal dropouts. If your frame was made prior to the late 80's, you are in luck. Otherwise, it becomes a more expensive proposition. If the frame is older, you can start by taking off the derailleurs, shifters, etc. Next you need to remove the big chainring and bolt the small one back on with shorty or single chainring bolts. Next is the rear hub. Your best bet is to get a track or flip-flop hub and lace up a new wheel. If you have a freewheel you can also thread on a single cog and change to a solid axle. The final step is to tension the rear wheel so the chain is tight without any binding and then check that your chain-line is straight. If you have horizontal dropouts, you are facing a more difficult problem. You can not use a chain tensioner on a fixed gear bike like you can on a single-speed. You will simply bend it when you try to resist the rotation of the rear wheel. The only real option you have here is to get one of the White Industries Eno eccentric hub that has an eccentric axle that allows for 15 mm of adjustment. The problem is they are expensive. Hope that helps. |
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