Gears manage the ratio of force required to turn the pedals and move the bicycle. Those who have a single-speed bike may wonder if they can convert it to a multi-speed, with multiple gears doing the work.
Yes, you can add gears to a single-speed bicycle, as long as the dropouts can handle a multi-speed wheel hub.
By adding a gear shifter, the cyclist can easily navigate terrain that is neither flat nor paved. Consider that converting from a single-speed to a multi-speed bike may be an expensive and complicated option.
Single-Speed Gear Bicycles
A single-speed gear is a practical option for some bike riders. Those who use bikes for city commutes, casual riding, recreational riding and exercising, and beach cruising on wet and compacted sand will find a single-speed gear appropriate for their needs if they use their bicycles on flat surfaces and paved roadways.
Advantages
Lighter in weight, the single-speed bike takes less effort to pedal and has fewer mechanisms that can malfunction. These bikes generally require less maintenance and offer a more cost effective option compared to those that have multiple gears.
Disadvantages
Single-speed gear systems work poorly on shifting terrain and unpaved bike paths. Trying to ride a single-speed uphill on rocky terrain requires great effort and may damage the bicycle. Similar to lower gears on a vehicle, the single-speed gear cannot exceed a certain peak of speed, even if the cyclists peddle faster and with greater force.
Benefits of a Multi-Speed Bike
Bicyclists have greater flexibility with multiple gear options. “Easier” gears offer better control while riding uphill or on inclines, while those cruising downward on steep hills benefit from the restraint provided by “harder” gears. Gears in the middle offer suitable navigation on terrain and road conditions between these extremes.
Adding gears allows the bicycle to reach a greater variety of speeds. Cyclists can ascend steep elevations and hills faster and easier, making the riding experience less stressful and more efficient if the bike is used in areas with elevations and softer pavement, such as fields, woods, meadows, dirt, or sand. A bike without gears functions well on a flat and paved surface, but struggles to get through areas with substantial elevation change, road debris, or unpaved pathways.
A range of gears allows the cyclist to transition between easy peddling and having the ability to power the bike over inclines and obstacles the rider may encounter. Smaller cogs require more intense peddling but have the ability to increase speed quickly after starting from a full stop, since the chain travels less distance to complete a full turn of the cog. Larger cogs offer easier peddling but take more effort to get the bike to a faster speed quickly, since the chain has to rotate a greater distance to make a full turn.
An OLD and Crucial Factor
An important determinant when planning to convert a single-speed bike into one that has multiple gear speeds is the Over Locknut Dimension, or OLD. This measurement represents the distance between the outer portions of the lock nuts that occupy the rear hub. There are two lock nuts on the bicycle, and space between the outer sides of them is the usable part of the rear hub that is available for expansion.
OLD dimensions on different types of bikes vary. For example, many BMX bikes have an OLD of 110 mm. The OLD on many bikes with a single speed is approximately 120 mm. Road bikes with disc brakes have a wider OLD of 135 mm. For bikes with an OLD of less than 130 mm, there are generally two ways to add gears: taking advantage of the internal gear hubs or cold-setting the bike’s frame.
Using an Internal Gear Hub
Advantages
Generally speaking, a bike with an OLD of 120 mm has a frame that handles two or three speeds within a small area. This option of using internal gear hubs protects the bicycle gears from the elements and excessive dirt, dust, and moisture. The bicyclist also has the ability to shift gears even if the bike is stationary. This is an ideal option for bikes with a smaller OLD because it does not require a significant adjustment to the bicycle’s overall geometry.
A low maintenance option, the hub can be paired with a belt rather than a chain. This unit has a single shifter and does not require a rear derailleur. Multi-gear cassettes that may fit on bicycles with a large OLD will not work on these cycles. Gear hubs also give the bike a cleaner appearance, since there are fewer external parts visible. The hub system does require periodic lubrication to maintain peak efficiency.
Disadvantages
Using internal gear hubs to add gears to a single-speed bike model has some disadvantages. These hubs add a significant amount of weight to the bicycle’s rear wheel, something that affects performance for those who want a lighter bicycle. The use of the shifter cable makes it more of a challenge to replace the rear tire, since the cable must be disconnected before the tire can be removed.
Other limitations exist when selecting the internal gear hub option. The hub accommodates fewer gears than even a low-end derailleur gearing system. It is possible to get a hub with more than three speeds with a hub system, though this system tends to be more complicated to maintain. Since the internal gear hubs have their own shifters, the user cannot add a more sophisticated shifter to the bicycle. The gear system is a piece of the overall hub installation—making it, in effect, part of the wheel. If the wheel suffers from damage, replacing or repairing the hub is a complicated process.
Maintenance needs tend to increase over the span of the hub’s useful life. Although maintenance requirements are minimal at the beginning, after significant use they have a tendency to malfunction. Also, lacking a rear derailleur, chains used with an internal gear hub system have a tendency to need frequent tension adjustment since there is not a derailleur to stretch the chain.
Drive Belt Compatibility
Since gear hubs do not require a derailleur, they work well with a drive belt for those who prefer that option over the use of chains. An important advantage of drive belts is that they tend to require fewer repairs and less maintenance than chains used with gear systems.
Cold-Setting the Bike Frame
A second option to add gears to a single-speed bike involves the process of cold-setting. This process involves the spreading of the dropouts so they can handle a wheel that has wider gear hubs and an attached derailleur gear system. Cold-setting must be done in a tactful manner to preserve the structural integrity of the bicycle frame. Before cold-setting a frame, the cyclist should make sure they have the appropriate tools and understand that this action may void the frame’s warranty.
Two Cold-Setting Approaches
There are two ways to perform the cold-setting process. One involves an attempt to spread the frame slightly, installing the wheel without doing a full cold-set. This option may work if there’s a slight difference between the dropouts and the hub’s OLD. If not done precisely, however, the dropouts may become misaligned, resulting in the need for constant chain-tensioning and making it a challenge to remove the wheel from the bicycle.
The second cold-setting option involves the use of a threaded rod and nuts. This is a safer and easier way to cold-set the bicycle. By threading the nuts, the dropouts are pushed outward in a way that preserves equal measure between them.
Both cold-setting options require that the bicycle has a steel frame that is in satisfactory condition. The bending of steel in decent condition can occur without the overall bike frame losing structural integrity because of steel’s tensile strength, its ability to handle stress without breaking. If the bike’s frame is made of materials other than steel or is not in good condition, a cold-setting should not occur, since this process has the potential to compromise the bike’s integrity and make it dangerous to use.
Derailleur Systems
After cold-setting a bike, a derailleur drivetrain system may be added that will offer an alternative to an internal gear hub. Although derailleurs are often found on the rear part of the bicycle, there are front derailleurs as well. When the cyclist pushes the spring-loaded arm toward or away from the handlebars, the chain shifts onto different cogs to meet the needs of the rider as they peddle. The metal frame derailleur holds the gears and works with a shifter, the lever used to change the gears through upshifting and downshifting.
Rear Derailleur Advantages
The presence of a rear derailleur system offers some advantages for a cyclist. The most obvious advantage is that these systems can have a much wider gear range, up to 30 speeds. This gives the rider much more flexibility to adjust gears to meet the demands of the terrain. Weighing less than gear hubs, derailleurs are more power efficient, allow for faster acceleration, and permit cyclists to attain higher speeds.
Derailleurs provide a greater mechanical advantage. Unlike the hubs that tend to lose much of the drive power as the energy generated is diffused, derailleurs move energy through the gear system with greater efficiency. Derailleurs are also much friendlier drivetrain systems, easier to fix with bike tools than gear hubs. Mid-range derailleur systems are an affordable option compared to gear hubs.
Rear Derailleur Disadvantages
There are some disadvantages to using a derailleur setup. They tend to be more fragile and are more susceptible to the elements, dirt, mud, and moisture. Unlike the gear hub that allows for the changing of gears while stopped, the derailleur system requires the bike to be in motion with the cyclist peddling for shifting into a different gear.
The bicycle must use a chain rather than a belt drive. Depending on road conditions and frequency of use, the chains used in derailleur systems require regular maintenance and tend to last for a shorter period of time.
Top image: © Eli Duke | Creative Commons