Singlespeed Conversions

Why ride a Singlespeed?

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!) a multi-speed bike is what you need…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 drive train 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 pullies 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 catch on the underbrush or to 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.

Singlespeed vs Fixed Gear

The one-speed revolution actually involves two different styles of bikes, singlespeeds and fixed gears. These are not the same thing, althogh 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 equalled 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 reversable “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.

Freewheel vs Coaster Brake

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:

  • You can only apply the brake forcefully in two crank positions.
  • If your foot slips off the pedal, you can’t brake at all.
  • If your chain breaks or falls off, the brake fails.
  • If you don’t have a hand operated front brake, you can’t stop as short as a bike that does have one.
  • They are very awkward to get started, since you can’t easily rotate your cranks to a good starting position.
  • Wheel removal/replacement is more complicated, due to the need to attach the brake arm to the frame, and the fact that you can’t get a coaster brake with a quick release.

Coaster brakes are OK for beach cruisers, and flatland applications in general, but not a good choice for sporty bikes, nor for rolling or hilly terrain.Modern MTB cantilevers, either traditional center-pull 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.

Hubs for Singlespeed Bicycles

There are four ways you can go, as far as hubs are concerned. You can use a cassette hub, a multi-speed freewheel hub, a single-speed BMX hub, a singlespeed MTB hub, or a flip-flop hub.

Flip-flop Hubs

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 would be larger than the fixed sprocket, providing a lower gear.

You would 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 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, but 17, 18, 20 and 22 tooth freewheels are available.

Note, there are two types of hubs called “flip-flop”:

  • Fixed/free, this is the type I speak of above, with a “track” side and a freewheel side.
  • BMX type…BMX flip-flop hubs have two different freewheel threads, a standard one on one side, and a special smaller-diameter freewheel thread on the other, designed to work with special small freewheels (14, 15 teeth.) These are now quite rare, but if you are calling around looking for “flip-flop” hubs, make sure you get the right kind.

Conventional Freewheel-type Hubs

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 chain line is likely to only work with your granny gear unless you re-space the rear axle and re-dish the wheel.

Cassette Hubs

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 use. The best choice for this is to use BMX cassette sprockets. These sprockets are quite inexpensive, and are available in a range of sizes. They have taller teeth than sprockets designed for derailer use.

image

Singlespeed Cassette Hub Conversion

Disc Brakes

Disc brakes are increasingly popular for off-road use, and 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 rear disc brakes 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 reason to avoid front disc brakes, but I strongly advise against getting a rear disc setup for a singlespeed.

Solid-Axle vs Quick Release

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 fork end. 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.

If you use a good quality (Shimano is the best) skewer , tightened securely, it will hold just fine in any type of dropout or fork end .

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.

Frames for Singlespeed Conversion

Mountain Bikes

A fixed-gear mountain bike may be the ultimate in heavy-duty urban transport, and, if you are adventurous enough, you can even take it to the woods. Mountain bikes tend to have adequate ground clearance, although most, alas, have vertical dropouts.bridgestone CB-3 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 singlespeed this low makes the brake almost un-necessary: such a low gear lets me slow the bike down qickly 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 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:

Gain Inches Meters
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.
42/30 Free 2.64 34.4 2.75 Off-road.

The 52/30 and 42/20 combinations are not usable due to chain length. I change gears manually…yes, I have to stop to do it, so I don’t do it that often.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:

Gain Inches Meters
48/20 Fixed 4.65 62.4 4.99
42/26 Fixed 3.13 42 3.36
36/32 Fixed 2.18 29.3 2.34

Vertical Dropouts

Most 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.

dropout image dropout image dropout image dropout image
Horizontal Dropout
Campagnolo 1010
Horizontal Dropout
Short
Semi-Vertical Dropout Vertical Dropout
Spoke divider
dropout image dropout image dropout image dropout image
With Hanger Without Hanger Raleigh 3-speed Track Fork End
Not a dropout!

Most newer frames made for derailer use have vertical dropouts. This is convenient when you’re actually using a derailer, but this 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, 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 to them. 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:

Hub with flatted axleI 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 supporting 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.

Hub/Frame Spacing

Most mountain bikes have 135 mm spacing between the rear dropouts. Fixed gear hubs are commonly avaialable in this spacing, 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 relase.

Drive Train

Chainline

Old English Derailer 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 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.

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

Chain Tension With Straight Chain

Ideally, a singlespeed should have a frame with horizontal dropouts or track-style horizontal fork ends.With this type of frame, the chain tension is regulated by moving the rear axle back and forth in the fork ends. If the chain is too tight, the drive train will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding. If the chain is too loose, it can fall off, usually at the most inconvenient possible time.

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.

Chain/Sprocket Life Extension

If you want to get the maximum life from your chain and sprockets, select even numbered sizes when possible. See my Chain Life Extension Article.

Chain Tensioners for Vertical Dropouts

If you’re converting a ’90s mountain bike to singlespeed, chances are that it has vertical dropouts, and you’ll most likely need a chain tensioner of some sort. There are two different sorts of chain tensioners that you can use. image

Adjustable Tensioner

Adjustable Tensioners

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 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 hangr.

Spring-Loaded Tensioners

These are like partial derailers, with a single spring-loaded pulley. They attach to the derailer hanger of your dropout. Like many purpose-built singlespeed parts, they are often rather expensive considering how simple they are. If you plan to use different gear ratios, for instance with a flip-flop hub, a spring-loaded tensioner is the best choice.

Recycled Rear Derailers

You can also use your old rear derailer as a chain tensioner, but it is heavier than you need, introduces more friction, and detracts from the looks of the bike. You need to adjust the high-gear limit stop for the correct chain line.

Good Luck

If you are lucky, you may be able to get a frame with vertical dropouts to work as a singlespeed without a chain tensioner. You will probably have to be a bit flexible in your gear choice. I address this in detail in my Fixed-Gear Conversion article at “#vertical.”

Not For Fixed Gears Nor Coaster Brakes

Chain tensioners are only usable with freewheeling hubs. They must not be used with fixed gears or coaster brakes, because these allow chain tension to be applied to the lower run of chain when you backpedal, and no chain tensioner is built to withstand this force.

Big or Small?

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 48/16 all give the same 3:1 ratio. Which to choose?

Bigger Smaller
Good:
  • Slightly less friction
  • Longer chain/sprocket life
  • less chain tension
  • Slightly lighter
  • More log-jumping clearance
  • More chainstay clearance
Bad:
  • Slightly heavier
  • Chainstay clearance may be a problem on some frames
  • Rapid chain/sprocket wear
  • Greater chain tension (increased liklihood of the axle slipping in the frame)

These differences are mostly pretty minor. Most riders will be best served by a chainring somehere 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

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:

  • Your weight
  • Your strength
  • Your endurance
  • How far you’ll be riding in a day
  • How hard you’re willing to push
  • How much baggage you’ll be carrying
  • The steepness of the terrain
  • The nature of the road (or off-road) surface

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 you speed will be limited by the tendency to “spin out.”

Flip-Flop Fixed/Free Singlespeedshercules

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.

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