This article deals with the nuts-and-bolts of converting a conventional road or mountain bike into a fixed gear.
If you wonder why you might want to do such a thing, see my separate article:
The best set-up for a road fixed-gear is to build up a new rear wheel, using either a track hub or a flip-flop hub.
Track hubs have a stepped thread. The main thread that the sprocket screws onto is the same as that of a normal freewheel hub. Outboard of this, is another threaded section of slightly smaller diameter. This thread is a left (reverse) thread, and a special lock ring screws onto it. After you screw the sprocket on in the normal manner, and tighten it down securely, the lock ring screws down so that it presses against the outer surface of the sprocket. If the sprocket should start to loosen up, it will try to turn the lock ring counter clockwise...but that only tightens the lockring. As a result, the sprocket cannot be unscrewed by the chain, no matter how hard you fight the pedals.
|English/ISO||1.29" x 24 TPI|
|Campagnolo/Phil Wood||1.32" x 24 TPI|
|Old French||33 mm x 1.0 mm|
lip-flop, or double-sided hubs are threaded on both sides. Usually one side has a track-type threading, (with lockring) and the other side is threaded for a single-speed standard freewheel. It is possible to find them with track threading on both sides, but not easily.
The usual way to use a flip-flop hub is to have a fixed gear on one side, and a single speed freewheel on the other. Ideally, the freewheel sprocket would be one or two teeth larger than the fixed sprocket.
You would ride with the fixed gear most of the time (I hope!) and save the freewheel for longer rides, or for getting you home when you are tired. Having the freewheel a bit larger than the fixed sprocket gives you a lower gear when you are using the freewheel. This makes it easier to climb. Since you can coast when you are using the freewheel, the lower gear is no disadvantage on the descents.
Single-speed freewheels are commonly used on BMX bicycles, most shops that deal in BMX parts should stock them. The common size used for BMX is 16 tooth, other sizes may be hard to find, especially for 3/32 chain.
If you are going to use a flip-flop hub with a freewheel, you should have two brakes on the bicycle.
Note, there are two types of hubs called "flip-flop":
he cheapest way to convert a multi-speed bicycle into a fixed gear is to use the original rear hub, assuming that it is made for a conventional threaded freewheel. A fixed sprocket will thread right on, but there is no provision for a left threaded lock ring.
If you go this route, it is a good idea to use LocTite or a similar thread adhesive. You can use an old lock ring from a British-threaded bottom bracket as an additional safety measure, it is the same thread.
Although you can just screw on the sprocket and put everything together, the chain line will probably be incorrect. If you go this route, you will usually need to re-arrange spacers on the axle to correct the chain line, then re-dish the wheel so that everything will track correctly.
I should mention that there are those who say you shouldn't use a lockring. This theory is based on the fact that if the chain should come off the chainwheel and get caught, a sprocket without a lockring will just unscrew, rather than locking up the rear wheel.
My feeling is that it is better to use a lockring so that you can rely on being able to slow the bike down with your feet, especially if you ride with only one brake.If you don't use a proper track hub with a lockring, you really should have two hand brakes. If not, a front brake failure followed by a sudden extra effort at "resisting" could break the sprocket loose at the worst possible time, and you'd be toast!
The Quality part number is HU9020. Expect to pay $70-80, plus sprocket and lockring.
This device is mainly intended for use with disc wheels and the like. Although it works with most Shimano cassette Freehubs, it is expensive enough that it doesn't generally make sense unless you already have a very good wheel that you don't have any use for as a multispeed. Bruce Ingle, a fellow member of the Charles River Wheelmen used a Shimano cassette hub, which he immobilized by brazing the ratchet mechanism together.
I rode with a brazed-up cassette hub for quite a while, and it worked fine.
As a result, it is widely believed that quick-release axles are not suitable for fixed-gear use. This is false!
It is my belief that the velodrome rule dates back to long before the invention of the quick-release, when the choices were standard nuts or wing nuts. The protruding "wings" of wing nuts might constitute a hazard in a crash, and I believe that's why the rule was instituted. Since quick-release skewers don't have any sharp projections, that becomes a non-issue in practice.
If you are going to use a quick release with a fixed gear, you should make sure to use a good quality enclosed-cam skewer.
t is very desirable that a frame for fixed-gear use have "horizontal" rear dropouts: that is, the slots in the frame that hold the rear axle should run in a more-or-less horizontal direction. This allows you to move the axle back and forth as needed to adjust chain tension. This makes things much easier than if you try to convert a newer bike with vertical dropouts.
The most desirable bikes for fixed-gear conversion are 1970's road bikes. These usually have horizontal dropouts, and usually don't have unsightly shift-lever bosses. Frames of this era also tended to have more generous tire clearance than newer sport bikes, providing more versatility in the choice of tires, and the use of fenders.
If you replace the 590 mm (26 x 1 3/8") wheels with 622 (700C) wheels, the bottom bracket gets raised a useful amount, providing good ground clearance. Using the larger wheels also allows you to install a better, shorter-reach brake caliper.
One of my favorite bikes is my 1916 Mead Ranger. This was originally built as a coaster brake bike with 28 inch single-tube tires on wood rims. It was wheelless when I bought it at a flea market, so I set it up with some nice quality '70s vintage 630 mm (27") wheels and modern tires. It's surprisingly pleasant to ride.
I have an old Bridgestone CB-3 set up for nasty winter conditions, with a 28/15. This gives a nice low gear, a 3.63 gain ratio (49" / 3.88 m) which will take me as fast as I care to go when the streets are snowy. A fixed gear this low makes the brake almost unnecessary: such a low gear lets me slow the bike down quickly by resisting, especially considering that it can't go very fast.
I have set up a couple of mountain bikes with flip-flop hubs, so that I get a fixed gear on one side and two different freewheel gears on the other. This is done with a double chainwheel and a two-speed freewheel. (The freewheel is actually an old 5- or 6-speed freewheel with 3 of the sprockets replaced by spacers.
In front, I have a 42/52 double, which I use with a 19 tooth fixed and a 20/30 freewheel. This gives 3 usable combinations:
|52/19||Fixed||5.45||71.2||5.70||General road use|
|52/20||Free||4.90||64.1||5.13||Road...when I'm tired, or hilly areas.|
Bruce Ingle, a fellow member of the Charles River Wheelmen, has gone me one better, and made a triple-fixed mountain bike. He used a Shimano cassette hub, which he immobilized by brazing the ratchet mechanism together. I am a bit nervous as to the long-term prospects for this hub, in particular the connection between the freehub body and the hub shell, but I think I will have to copy his setup. He's got:
ost newer bikes (made since the late-1980's) have "vertical" rear dropouts, where the wheel slides upward as you install it. These are a problem when you want to dispense with a derailer, because you need some way to regulate chain tension.
|Semi-Vertical Dropout||Vertical Dropout|
|With Hanger||Without Hanger||Raleigh 3-speed||Track Fork End
Not a dropout!
You cannot use a derailer on a fixed gear bike, even as a chain tensioner, because when you resist the rotation of the pedals, you would bend the derailer. This presents a problem if you want to use a frame with vertical dropouts as a fixed gear, because there's no easy way to adjust the chain tension. This is also true of chain tensioners sold for singlespeed coasting bikes, such as the Surly Singleator.
Even the chain tensioners used for downhill mountain bike racing are not strong enough to withstand the stress of resisting the pedals. These tensioners have to clamp on to the chain stay, which is more or less round. There is no way to make one that would be secure, short of installing some sort of brazed-on fitting.
Fortunately, most "vertical" dropouts are not exactly vertical: they usually have a bit of a slant to them. You may have to play games with chainwheel sizes. One of my fixed-gear bicycles is based on a Cannondale touring frame. It happens that there is just enough adjustment to make it work with my preferred 42/15 combination. If the chainstays were a bit different in length, I could replace the 42 with a 41 or 43.
Adding or subtracting a link in the chain will move the axle 1/2". Changing either sprocket size by one tooth will move the axle 1/8" (4 mm). Thus, if I wanted a 5.75 gain ratio (75" / 6 meter gear), I might first try a 42/15, this gives a gain ratio of 5.77 (75.6" / 6.05 m gear). If the chain was too loose, I could take up 1/8" (4 mm) of axle movement by replacing the 42 with a 43. This 43/15 combination would raise my gain ratio to 5.91 (77.4" / 6.19 m). Alternately, I could get the same axle position with a 42/16 --5.41 (70.9" / 5.67 m).
If I was not happy with these choices, I could add a link to the chain and switch to a 45/17 --5.45 (71.5" / 5.72 m) If I added two links to the chain, I could get the same axle position with a 48/18 --5.49 (72.0" / 5.76 m)
It is also possible to use a special "half link" or "offset link" to lengthen or shorten your chain by only 1/2".
Another possibility would be to do a little bit of filing at the back of the dropout to let the axle move back just a bit.
It is also possible to grind or file a flat on each end of the axle to allow a bit more adjustment, like this:
I used a more drastic solution: on my Bianchi Osprey. I cut the rear axle short so that it didn't protrude past the surfaces of the locknuts. Thus, only the quick-release skewer went through the dropouts. Since the skewer is quite a bit thinner than the actual axle, this gives me considerably more adjustment room.
If the skewer is properly tightened, the axle is held in place by the friction of the locknuts being pressed against the inside of the dropouts. If this were not the case, horizontal dropouts would not be usable, since the forward pull on the chain creates a larger force against the axle than supporting the rider's weight does. Just to be on the safe side, I carried a spare skewer along with my spare tube.
I rode that setup for a couple of years with no problems, but later got a deal on a Bianchi B.a.S.S. purpose-built singlespeed frame that fits me better, is notably lighter and has horizontal track-type fork ends, so I'm no longer using that setup.
Quite a fine adjustment is possible positioning a "ghost chainwheel", as shown on our home-built tandem pag. It does reduce drive efficiency slightly. The closer it is to the rear hub, the more slack it takes up, the smaller the risk of its falling out, and the less likely it will rub on the chainstay.
Eric House has prepared a whole web site devoted to the problem of finding sprocket combinations that will work with vertical dropouts. He has developed charts and Java applets that show the options available for particular chainstay lengths.
Frames built originally to be used with 5-speed freewheels usually have 120 mm spacing between the rear dropouts. Fixed gear hubs are commonly available in this spacing, although they are more commonly found in the narrower, 110 mm spacing which is standard for track hubs. If you are using a newer frame, with wider spacing, you may want to replace the axle. You may want to replace the axle in any case, because fixed gear hubs generally come only with solid axles, not quick release.
any track bicycles use a wider chain than is common on multi-speed bicycles. Derailer-type chain has a nominal internal width of 3/32". Single-speed bicycles, including most track bicycles, use the wider 1/8" size. You can buy fixed-gear sprockets in both widths.
(Some people mistakenly refer to the width as "pitch", speaking of "road pitch" or "track pitch". This is a malapropism. The pitch is the distance between the rollers, and all modern bicycle chain has the same pitch, 1/2"/12.7 mm.)
I generally prefer using the 3/32" (derailer) size. The 1/8" size is slightly heavier, but doesn't seem to perform any better in my experience.
For the true retro fan, another option is 1" x 3/16" chain. This used to be common on track bikes. This requires special sprockets with only half as many teeth as standard 1/2" pitch sprockets. Serious old-time trackies used "block" chain, which had no rollers. This is no longer available. Roller chain is still sometimes findable in this size.
Even more obscure is the 10 mm pitch chain promoted by Shimano in the early 1980s. The idea was to save weight by making everything littler. An idea whose time never came.
erailer bikes can work fairly well even with the chain running at a considerable angle, but this should not be done with a fixed-gear setup. It is quite important to get the chain line just right.
I usually check the chainline by installing the hub in the bike, with no chain installed. By placing my head just in front of the chain wheel, I can sight along the chainwheel and see back to the rear hub, to see if the chainwheel lines up exactly with the rear sprocket. If it doesn't, I re-arrange spacers or change the bottom bracket axle as necessary. You might also hold a yardstick or other straightendge against the side of the chainwhee, reaching back to the sprockets.
Usually, on a bike that came with double chainwheels, the inner chainwheel will be more in line with the rear sprocket. If you wish to make the bike a pure fixed gear, you can buy a set of shorter "stack bolts" (the 5 bolts that hold the chainwheel(s) to the crank spider). You may find it easier to locate these in a shop that deals in BMX bikes.
Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.
This takes a little bit of your hands learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.
Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.
Once you have the chainrings centered and secured, adjust the position of the rear axle to make the chain as nearly tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible.
You need to pay more attention to chain wear on a fixed-gear bicycle than on others, because the consequences can be more serious if the chain falls off. If the chain is badly worn, adjusting it just short of binding will result in rough running and low efficiency, because the chain will not engage the teeth of the sprocket evenly. Check the chain for wear, readjust the position of the rear hub and replace the chain as needed.
If you have a local bike shop that stocks fixed-gear stuff, you are in a lucky minority, and I urge you to patronize them.
If you don't have such a shop nearby, check out:
|Fixed Gear Parts from Harris Cyclery|