from Rookie’s keyboard
Hello, friends
It’s time for another Bike Theory Class.
Today, I am going to talk about the possibility of equipping a single-speed bicycle with additional gearing.
Many people think that this isn’t in the realm of possibilities, but that’s not really the case. In other words, there are workarounds.
If the dropouts of the frame can accommodate a wheel hub designed for multiple speeds, then it’s possible to add gears.
If the frame is too narrow, however, one would have to look into internal gear hubs or consider “cold setting” the frame if it’s made out of steel.
Over Locknut Dimension
The most crucial factor is the Over Locknut Dimension or O.L.D. that the frame is designed for.
The term O.L.D. refers to the usable part of the rear hub and is essentially the distance between the outer sides of the two locknuts found on the hub.
The table below contains common rear O.L.D. dimensions and the bikes that they’re designed for:
| Rear O.L.D. | Bike Type |
| 110mm | BMX |
| 120mm | Track bikes + fixies |
| 130mm | Road bikes without disc brakes |
| 135mm | MTB, road bikes with disc brakes |
| 141mm | Boost hubs |
If the frame is engineered for O.L.D. under 130mm, you’re left with two options:
A. Use an internal gear hub
B. Cold set the frame
Internal Gear Hubs
Since most single-speed bicycles have an O.L.D. of about 120mm, the number of internal gear hubs that could accommodate such a frame is limited.
Below is a table containing 120mm O.L.D. internal gear hubs and the number of speeds that they offer:
120mm O.L.D. Internal Gear Hubs
| Model | Weight | Speeds |
| Sram Automatic 2 Speeds | 980g | 2 |
| Sturmey-Archer S3X Fixed Gear | 980g | 3 |
| Sturmey-Archer S2 Kick-Shift | 920g | 2 |
| Sturmey-Archer S30 X-RD3 | 1400g | 3 |
| Shimano SG-3C41 Nexus Gear Hub | 1120g | 3 |
| Sturmey-Archer S80 XRF8 | 1400g | 8 |
In general, most 120mm internal gear hubs are limited to 2-3 speeds because it’s difficult to pack more in such a small package.
If the frame is made of steel, it’s possible to cold set it so that it can accept internal gear hubs of greater width.
The Advantages of Internal Gear Hubs
The main advantages of a hub with internal gears are as follows:
Protection From the Elements
The internal gear hub acts as a capsule for the gears and ensures their proper functioning even in wet and dusty conditions.
Low maintenance
An internal gear hub requires little to no maintenance at least during the beginning stages
An Ability To Shift Gears Even When Stationary
Unlike a regular derailleur-based system, internal gear hubs allow cyclists to shift while waiting in traffic.
Belt-Drive Compatibility
An internal gear hub can be paired with a belt because it doesn’t use a derailleur. The main selling point of belts is that they require very little maintenance in comparison to chains.
Simplicity + Clean Look
Gear hubs make the bike look cleaner since there is only one shifter and no derailleur.
The Disadvantages Of Internal Gear Hubs
The main disadvantages of internal gear hubs are:
Weight
As you can see in the table above, internal gear hubs add serious weight to the rear wheel. This is a problem for people trying to keep their bicycles as light as possible.
More Complex Maintenance
In the beginning, internal gear hubs do not require as much attention as an “exposed” gear system, but they malfunction more often than one may think. And when that happens, the issue is usually difficult to fix unless you’re well acquainted with the hub in question.
Due to the complexity of the repairs, many people replace the internals of the hub and continue riding.
More Difficult Tire Replacement
The shifter cable connecting to the internal gear hub makes the process of replacing a tire more cumbersome – you have to disconnect the cable to remove the tire.
The Gearing System Is Part of the Wheel
When you use an internal gear hub, your entire gear system is part of the hub and therefore wheel. If the wheel is damaged, the replacement process will be more difficult, slower, and potentially more expensive.
If a problem occurs in an area with a poor supply of bike parts, it may be very difficult to get your gearing in order. Meanwhile, cheap derailleurs are readily available everywhere.
Note: Another problem is theft. If someone steals your rear wheel, they’re taking your gears with it.
Lack of Shifter Options
Gear hubs come with their own shifters. You don’t have the luxury of choosing your own.
Low Range of Gears
Even a cheap derailleur set-up offers a greater gear range than the average internal gear hub.
Frequent Chain Tension Adjustment
The chain will have to be adjusted more frequently because there isn’t a derailleur to stretch it out.
Cold Setting a Frame
Another option is to spread the dropouts apart until the frame can accept a wheel with a hub designed for gears. The process is known as “cold setting a frame”.
Sheldon Brown describes the method here.
“Cold setting” is an option only if the frame is made of steel and in decent condition. In all other cases, the frame would lose its integrity and will become dangerous to ride.
Steel can be bent (cold set) without notable loss of structural integrity because its ultimate tensile strength is notably higher than its yield strength.
The ultimate tensile strength of a material describes the amount of stress that it can withstand before losing integrity and eventually breaking.
The yield strength, on the other hand, is the point beyond which the material permanently deforms.
For example, Chromium-vanadium steel has a yield strength of about 620 MPa whereas its tensile strength is 940 MPa.
Meanwhile, 6061-T6 aluminum, a material often used for bicycle frames, has a yield strength of about 276 MPa and tensile strength measured at 310 MPa. Since the numbers are really close, cold setting an aluminum frame is never recommended.
If the difference between the hub’s O.L.D. and the dropout distance is very close, it’s possible to spread the frame a bit and install the wheel without cold setting the tubes.
This approach seems very tempting due to its simplicity, but it does have some notable drawbacks, namely:
1. Drop out misalignment
Cold setting a frame is a 2-phase process. During the first one, the frame is widened. During the second, the dropouts are realigned. When you don’t cold set the frame and simply force in the wheel, you’re automatically skipping phase 2.
Or in other words, the dropouts won’t be aligned. The result is uneven stress on the hub and the axle.
2. Constant stress on the chainstays
Avoiding the cold setting process results in constant chainstay tension.
3. Inconvenience
If the frame is not cold set, you will have to manually open it every time you change the wheel.
Using a Derailleur
Converting a bicycle with a dedicated single-speed frame to multiple gears operating with a derailleur requires the largest investment in terms of parts and labor.
Moreover, those frames are less likely to have O.L.D. wide enough to accommodate a geared hub.
But if the spacing is sufficient or the frame is suitable for “cold setting”, then a conversion to a gear system using a rear derailleur will technically be possible.
Below is a list of the required parts:
1. New wheel with a hub designed for gears
A new hub and consequently wheel will be needed because single-speed hubs aren’t designed to accommodate cassettes.
2. Derailleur + hanger
Obviously, a new rear derailleur will be needed for the conversion too.
The installation of the derailleur will necessitate the purchase of a special hanger which puts the derailleur in a position from which it can encompass all rear cogs.
Most dedicated single-speed frames do not have a built-in derailleur hanger or special bosses where you can install one.
This leaves us with two options – to purchase a derailleur that comes with a hanger or to find a way to add a derailleur hanger to the frame.
If the frame is a track one (fixie) it will have rear-facing dropouts. In that case, one of the possible solutions is to buy chain tugs with an added derailleur hanger.
What are chain tugs? The original function of chain tugs is to help the rider adjust the tension of the chain.
3. New chain
Single-speed bicycles use a significantly thicker chain than geared models.
The inner width of a single speed chain is about 3.175mm whereas that of multi-speed chains varies between 2.38mm and 2.18mm depending on how many gears the bicycle has.
More gears require a narrower chain because the spacing between the rear cogs is smaller.
In consequence, a single speed-chain is just too thick and wide to operate properly with a derailleur.
4. New chainrings
Single-speed chainrings are designed for chains with greater inner width and are therefore thicker than the multi-speed ones.
For that reason, the chainring will also have to be replaced even if you don’t plan on adding a front derailleur to the bicycle.
5. Shifters
At least one new shifter will be needed. If you are running flat handlebars, the investment wouldn’t be substantial, but if you are on drop bars, the price of shifters goes up significantly.
This is especially true for the so-called brake-shifters which integrate shifters and brake levers into one to allow drop bar users to comfortably switch gears without excessive movements.
If you want to use your existing brake levers, a popular choice would be bar-end sifters which are very common among touring cyclists.
6. Shifting Cables +Housing
New shifting cables and housing will also have to be added to the buy list.
7. Bolt-on cable stoppers
Single-speed frames do not have cable routing for gears. There are two main ways to circumvent this problem:
- Run a cable from the shifter all the way to the derailleur and zip-tie it to the frame.
This solution is simple and cheaper, but many won’t consider it aesthetically pleasing.
2. Purchase cable stoppers that can be mounted to the frame’s top tube via-bolts.
8. Tools
If you plan on doing the conversion yourself, you will need tools that you may not currently have.
Below is a list of tools needed for the job:
- Variety of Allen keys
- Wrenches
- Cable and housing cutters
- Screwdrivers
- Dropout Alignement tool
Note: Regular cable cutting pliers don’t do a good job as bike cable and housing cutters. Specialized cutters are required to make a clean cut.
Internal Gear Hub
Conversion with the help of an internal gear hub could also be very expensive due to the price of the hub.
Here’s a list of the needed components:
1. Internal gear hub
2. New wheel or re-lacing of the old wheel
2. Shifter
3. Shifting cable + housing
Re-converting a Conversion
If the frame is originally designed for more than one speeds but has been purposefully converted to single-speed, a conversion back to multi-gears is substantially easier because the dropouts are already wide enough to accommodate a hub designed for gears.
Having said that, “cold setting” may still be required if the frame is built for fewer gears than the number you want to add.
Here’s a plan of attack and the parts that will be needed:
1. Cold setting (only if you want to fit a hub with more gears than originally intended)
2. New derailleur
3. Derailleur hanger (potentially). The derailleur hanger on older multi-speed frames is often part of the frame.
4. New chain
5. New shifter
6. New chainrings
Summary (image)
Final Words
If the frame is originally engineered for one gear, the investment could become substantial and lacks financial sense if you don’t already have the needed parts.
In some situations (e.g., a strong desire to continue using a certain frame because it fits you well), a conversion to a geared system may be a well-defended decision.
Until next time,
Rookie
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