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Modern 24-27 speed bikes are marvels of technology, and allow a cyclist to select the gear ratio that will make the most efficient use of his/her energy. If what you're after is getting the maximum possible speed/distance for the minimum effort (and there's nothing wrong with that!) you need a multi-speed bike...but, efficiency isn't everything!
If you're riding for sheer pleasure, or for exercise, you don't necessarily place that high a premium on output results, as measured in speed, distance or vertical climb. Instead, you may care more about the actual experience of riding your bike. In this case, you may be a candidate for a singlespeed bike.
Riding a singlespeed can help bring back the unfettered joy you experienced riding your bike as a child. You don't realize how much mental energy you devote to shifting until you relinquish your derailers, and discover that a whole corner of your brain that was formerly wondering when to shift is now free to enjoy your surroundings and sensations.
Paradoxically, a singlespeed is, in another sense, more efficient than a multispeed bike! While the single gear ratio will not be the "perfect" gear ratio for all conditions, in the conditions which fit the single gear, it is considerably more efficient mechanically than the drivetrain of a derailer bike.
A singlespeed bike dispenses with the weight of the derailers, shifters, cables, extra sprockets and longer chain. In addition, a singlespeed gear train runs the chain in a perfectly straight line from sprocket to chainwheel, and avoids the serpentine wind through the pulleys of a derailer. You can really feel the difference! A singlespeed is noticeably quicker and easier to pedal than a multispeed bike in the same gain ratio.
Singlespeed bikes are also considerably more sturdy and reliable than multispeed bikes. There's no derailer to bash if the bike falls over, catch on the underbrush or get overshifted into the spokes. The rear wheel itself is a lot stronger than one made with off-center (dished) spoking to make room for a whole bunch of sprockets on one side.
The one-speed revolution actually involves two different styles of bikes, singlespeeds and fixed gears. These are not the same thing, although they have much in common.
A fixed gear bike differs in that it does not permit coasting: when the bike is rolling, the pedals will turn, just as with a child's tricycle. To enjoy the one-speed experience to the max, a fixed gear is the best choice if you ride mostly on pavement. A fixed gear gives a degree of control and one-ness with the bike that is not equaled by a freewheeling bike.
This site also contains several articles dealing with fixed-gear bikes.
Fixed gear is not ideal for all circumstances, however. A fixed gear is not well suited for seriously hilly terrain, and, more importantly, is not good for technical mountain biking. A mountain biker in difficult terrain must be able to control when each pedal is down, to avoid striking a pedal on rocks, logs or other obstructions. Similarly, jumping over obstacles is much more difficult on a fixed gear. If your single gear is low enough for off-road climbing, it will be too low to spin on the descents.
You don't have to choose once and for all between fixed and freewheel, because the same bike can be both, if you use a reversible "flip-flop" hub.
Many cyclists interested in simplifying consider going to a singlespeed freewheel as a way to "test the waters" with the idea that if they turn out to like that, they might later convert to fixed gear.
This is generally the wrong way to approach it, in my opinion.
I STRONGLY recommend starting out with fixed gear. If it turns out to be a problem, you can easily convert to freewheel later if you want to...but my bet is you won't want to if you give fixed gear a good try (typically takes a couple of weeks of regular riding to get past the strangeness, but then it's quite addictive!)
Most folks who set up their bikes with a fixed/free flip-flop wind up using the fixed gear side pretty much all of the time. The freewheel option is mainly useful for when you have taken a longer-than-usual ride, and need to get home even though you're all tuckered out.
While coaster (backpedaling) brake bikes are also, mostly, single-speed machines, I don't recommend them for technical off-road use. Coaster-brake hubs have a good deal of internal friction, and coaster brakes have a number of serious drawbacks:
Short-reach caliper brakes and modern MTB rim brakes, either traditional cantilever or newer direct-pull styles can lock up either wheel at will, but also permit fine control over the modulation of each wheel's brake.
Flip-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.
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. The freewheel sprocket is larger than the fixed sprocket, providing a lower gear.
On an MTB, you use the fixed-gear side for most pavement riding, and save the freewheel for off-road use, or for getting you home when you are tired. Having the freewheel larger than the fixed sprocket gives you a lower gear when you are using the freewheel. This makes climbing easier. 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, but 17, 18, 20 and 22 tooth freewheels are available.
Note, there are two types of hubs called "flip-flop":
The cheapest way to convert a multi-speed bicycle into a singlespeed is to use the original rear hub, assuming that it is made for a conventional threaded freewheel. A single BMX freewheel will thread right on. Unfortunately, the chainline is likely to only work with your granny gear unless you re-space the rear axle and re-dish the wheel.
It is easy to convert a Shimano cassette Freehub ® for singlespeed use. The simplest way is just to remove the derailers, shorten the chain and thread it onto the chainwheel and rear sprocket of your choice. This is less than ideal, however, because you've got the extra weight of the unused sprockets to deal with, and the chainline will probably be crooked. The sprockets used on multi-speed cassettes are designed for easy shifting, which is not a good thing on a bike that isn't supposed to shift!
The better way to convert a cassette Freehub ® is to remove the 7-, 8- or 9-speed cassette and replace it with a single sprocket. You will also need a bunch of spacer washers to hold the single sprocket in place. You can often get a suitable number of spacers by taking apart a couple of discarded, worn-out cassettes.
Having a single sprocket sandwiched in a stack of spacers makes it easy to get the sprocket properly aligned for perfect chainline with whichever chainwheel you choose to use in front.
You can use one of the old sprockets from your taken-apart cassette, but it you are less likely to have accidental derailment if you use sprockets made for single-gear us, with longer teeth. BMX cassette sprockets are best. These sprockets are quite inexpensive, and are available in a range of sizes.
Disc brakes are increasingly popular for off-road use. They don't depend on good rim true, and don't get contaminated by mud. A number of high-end ready-made singlespeed bikes are supplied with front and rear disc brakes. In my opinion, this is not a good thing.
Personally I consider a rear disc brake a very poor choice for a singlespeed. It would preclude you from using a flip-flop hub. Also, as the chain wears and the axle is moved backward to take up the slack, the relationship of the disc to the caliper will change. That can't be good.
Singlespeeds are generally not practical for terrain so steep as to require dual disc brakes. There's no such problem with a front disc brake, but I strongly advise against getting a rear disc setup for a singlespeed. (There are different problems -- be aware of them. See information in the article on skewers and Jobst Brandt's article about brakes.)
Conventional wisdom is that you need a solid (nutted or "bolt-on") axle hub for fixed-gear or singlespeed use, and that a quick-release will not hold the wheel solidly enough in a horizontal forkend. This is not true, however.
Since most newer bikes have vertical dropouts, people have gotten used to wimpy aluminum skewers, and often don't adjust them as tightly as they might.
A quick release is a considerable timesaver in switching a flip-flop wheel around, and having a QR means that you don't need to carry a big wrench to be able to replace a damaged inner tube.
I have set up a couple of mountain bikes with flip-flop hubs, so that I get a singlespeed 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.|
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 Forkend
Not a dropout!
Most newer frames made for derailer use have vertical dropouts. This is convenient when you're actually using a derailer, but causes a complication when you wish to simplify your drive train, either to singlespeed, fixed-gear or an internal-geared hub. The simplest way around this is to install a chain-tensioning pulley of some sort. This is not an option for fixed gears or coaster brakes, but is the easiest solution for freewheeling bikes. Even for singlespeeds, though, it is nicer to be able to do without a klugy and inelegant chain tensioner.
Fortunately, most "vertical" dropouts are not exactly vertical: they usually have a bit of a slant. As a result, it is sometimes possible to use this type of frame. To make it work, 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 is the equivalent of moving 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)
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 have been experimenting with a more drastic solution: on my Bianchi Osprey, I have cut the rear axle short so that it doesn't protrude past the surfaces of the locknuts. Thus, only the quick-release skewer goes 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 the rider's weight does. Just to be on the safe side, I am carrying a spare skewer along with my spare tube.
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. Check him out at: fixin/. He is also supplying hubs with special eccentric axles to facilitate fine tuning chain tension.
It can be difficult or impossible to use a frame with vertical dropouts with a flip-flop hub.
Most mountain bikes have 135 mm spacing between the rear dropouts; most newer road bikes, 130 mm. Flip-flop ear hubs are commonly available in these spacings, although they are more commonly found in the narrower, 110-120 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 singlespeed hubs generally come only with solid axles, not quick release.
erailer bikes can work fairly well even with the chain running at a considerable angle, but this should not be done with a singlespeed setup. It is quite important to get the chainline 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 chainwheel, I can sight along the chainwheel and see back to the rear hub, to see whether 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.Most older one-speed hubs, such as BMX, fixed-gear and coaster-brake hubs have a chainline of about 40-42 mm (centerline of the frame/hub to center of the sprocket.)
The wider chainstays on mountain bikes often don't let you place a medium-sized chainwheel that close to the centerline of the bike, so there is a secondary de-facto standard chainline of about 52 mm for singlespeed mountain bikes. Stock MTB triple cranks usually have the outer chainring at around 52-57 mm; the middle is normally 47.5-50 mm.
If you convert a cassette Freehub ® to singlespeed, you can put the rear chainline anywhere you want to match that of the desired chainring.
There is more detailed information on chainline in my Chainline Article
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 chainring 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. I 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 drivetrain 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.
If the chain is badly worn, adjusting it so it is just short of binding will result in rough running and low efficiency, because it will not engage the teeth of the sprocket evenly. Check the chain for wear, and replace it as needed.
Adjustable tensioners are set for the particular chain length/sprocket combination you will be using, and then tightened up to hold the pulley in the correct position. These are mainly intended for use on (yuck!) downhill bikes, and are designed to supplement a derailer to keep increase the chain tension, reducing the risk of accidental derailment.
Some, such as the no-longer-available Tektro unit shown above, are also useful for singlespeeds. If you have a pure singlespeed, without a flip-flop hub, this type is adequate, and may even be very slightly more efficient, because there is no spring loading on the chain. I used to like the Tektro unit, but it proved a bit too delicate in practice, and clamping onto the chainstay isn't all that secure. I now prefer units that attach to the derailer hanger.
Once you have decided on your gear ratio, then there's the question of which of several different equivalent sprocket/chainring combinations to use.
For instance, 36/12, 39/13, 42/14, 45/15 and 48/16 all give the same 3:1 ratio. Which to choose?
These differences are mostly pretty minor. Most riders will be best served by a chainring somewhere in the 30s for technical off-road use, 40s for road or bike path use, low 50s for track use.
Since 42-tooth rings are very commonly available on road cranksets, this size is particularly popular for conversions.
If you use a flip/flop hub, running smaller sizes gives you a bigger gearing difference for each tooth difference on the flip flop.
Gearing is a very personal matter, and it is difficult to give good specific recommendations for someone I haven't actually ridden with.
The best gearing for you depends on a large number of variables, including:
There is no magic formula for this, only experimentation will let you determine what gearing suits your needs.
You might find my online gear calculator useful for comparing with your present gearing.
Generally, for street use, with a freewheel, I would recommend a gain ratio of around 5-5.3, for instance, a 42 tooth chainring with a 16 or 17 tooth sprocket.
You'll see other sites recommending "2:1" gearing, which typically gives a gain ratio of about 3.7. That's good if you are going to be riding off road on steep mountain trails, but a gear that low is maddening on the flats and particularly on pavement, because your speed will be limited by the tendency to "spin out."
With a double-sided hub you can build a bike with both a fixed gear and a freewheel gear. To change from one to the other, you must remove the rear wheel and flip it around, then re-install it. See my separate article about this option.
Unfortunately, singlespeed riding is somewhat of a fringe activity from a commercial point of view, and those who have not learned to love it tend to write singlespeeders off as nuts and fanatics.
If you have a local bike shop that stocks singlespeed stuff, you are in a lucky minority, and I urge you to patronize it.
If you don't have such a shop nearby, check out:
Singlespeed Parts from Harris Cyclery
More information -- and, do you really need to coast? See also:
Sheldon Brown's Fixed Gear and Singlespeed Articles
Chain Life Extension
Singlespeed Cyclocross by Tarik Saleh
1 x 1 / Surly
On One (UK)
SingleSpeed Drivetrains from Surly
|Articles by Sheldon Brown and others|
As far as I know, this was the very first Web page ever about converting geared mountain bikes to singlespeed!