A single-speed bicycle is often presented as an example of simplicity because it’s free of derailleurs, handlebar shifters, and the cables associated with them.
In addition, the mind of the rider isn’t preoccupied with selecting an appropriate gear. All you have to do is pedal.
And while that’s true for the most part, single-speed bikes still come with a surprising number of technical points that have to be respected for the proper operation of the machine.
As a result, a single-speed conversion is sometimes more complex than originally envisioned.
One of the problems that arise upon removal of the rear derailleur is the loss of chain tension. To battle the problem, people often resort to chain tensioners.
This leads us to the main topic of this article:
Is a chain tensioner necessary? And if so, when?
A pulley chain tensioner is necessary when the frame has vertical dropouts because they stop the wheel from moving forward and back.
In consequence, one cannot control the tension of the chain without a derailleur or a chain tensioner.
But if the frame has horizontal or semi-horizontal dropouts a pulley chain tensioner becomes unnecessary.
What Is The Purpose of a Chain Tensioner/Singulator?
One of the functions of a rear derailleur is to manipulate the chain tension when shifting to a different gear.
This happens through a spring mechanism and a pulley which reduces the chain tension when shifting and recovers it once the chain has moved to the desired cog.
Without this function, it would be impossible to change gears, and the chain of the bicycle would be dropping all the time.
In the image above, you see the dirty t-pulley of my abused rear derailleur.
The t-pulley is responsible for ensuring proper chain tension as the name suggests.
The upper pulley, on the other hand, is called g-pulley because it guides the chain onto a cog.
Once the derailleur is removed, there’s nothing to outstretch the chain, and it becomes very difficult to achieve proper chain tension.
You could, theoretically, tension the chain by using half chain links, but the process is slow, inefficient, and frustrating.
Another problem is wear and tear – over time, the chain wears off and lengthens. Before you know it, you will have to pass through the same extended procedure to readjust the chain tension.
Therefore, the fastest and most efficient way to turn a bicycle with vertical dropouts into a single-speed machine is to use a pulley chain tensioner also known as a “singulator”.
The chain tensioner attaches to the derailleur hanger and plays the role of a t-pulley stretching the chain and ensuring proper tension.
Chain tensioners come with either a push-down or push-up spring. In the first case, the pulley of the singulator is “inside the chain” and pushes it down like a regular rear derailleur.
The push-up option goes below the chain and pushes it up.
The push-down version is more popular because it accommodates more drivetrains and bicycles.
However, the push-up model has a distinctive benefit – it ensures more “chain wrap” over the rear cog and thus reduces the chances of teeth skipping.
Most singulators can be switched from a push-down to a push-up mode and vice versa by swapping the spring for the opposite one.
Using the Existing Derailleur As a Chain Tensioner
Chain tensioners often seem too expensive for what they are. The main reason for the high price is the “niche” nature of the product.
If you’re on a budget and don’t want to buy a singulator, the cheapest option to build a single-speed bike would be to use the existing derailleur by “dumbing it down” into a simple tensioner.
There are two routes to achieving this goal.
Option 1: Limit screws only
Step 1: Disconnect and remove the shifting cable going to the rear derailleur.
Step 2: Use the limit screws on the rear derailleur to align the pulleys with the rear cog.
The purpose of this part is to achieve a straight chain line. A crossed chain results in inefficient power output and places too much stress on the drivetrain components.
Step 3: Install the chain as you would normally do, but this time bring both sides together until the t-pulley is positioned forward.
If you do it correctly, the t-pulley of the derailleur will stretch forward as shown in the image above.
Mark that position on the chain and shorten it accordingly. If you think that the tension would be too great, add a link or two.
I highly recommend using a chain holding hook while doing this procedure. You could make one from an old spoke or the handle of a large file clamp.
If you want to be even more “ghetto”, you could skip replacing your cassette and chainrings too. You could simply leave the chain on the second ring at the front (if you’re running a 3x drivetrain) and in the middle of the cassette.
The downside of the “ghetto” approach is that you won’t get the weight savings and aesthetic points that come with a single-speed machine.
Option 2: Limit Screws + Cable
The second blueprint is a little more sophisticated and offers finer adjustments.
The method is largely the same as Option 1, but this time, the cable inserting into the rear derailleur is not removed but cut to a short piece.
That way you can still use the barrel adjuster at the back of the derailleur to micro-adjust the position of the pulleys.
The key to making this work is to use the stopper on the gear cable as an anchor as shown in the image below.
Notes: The gear cable in the image is not cut short because I plan to use it for something else, but otherwise, it should be.
Another benefit of this method is that you can have two cogs at the back of the wheel and switch between them by turning the barrel adjuster accordingly and spinning the pedals.
Of course, in that case, the bike wouldn’t technically classify as a single-speed model.
You can use any derailleur you want as long as you can attach it to your bike, but one with a short cage is preferred because it would offer more clearance and reduce the chances of catching an external object like a branch while riding.
Horizontal Dropouts Do Not Require a Chain Tensioner
Frames with horizontal dropouts allow the rider to create chain tension by sliding the wheel back.
This essentially eliminates the need for a pulley chain tensioner such as the one shown above.
There are two main type of horizontal dropouts:
The first one is known as rear facing dropouts or simply track ends.
You can find those on track bicycles, BMX bikes, dirt jumpers, trial bikes, and some mountain bikes.
If you want to have a single-speed bicycle or a fixed-gear, a frame with track ends is the best option because it offers the most safety and convenience while completely eliminating the need to use singulators.
A bike frame with track ends may not need a spring-loaded chain tensioner, but some people like to use chain tugs (image below) that wrap around the axle and allow you to pull rear wheel back with a bolt and nut mechanism.
This device, which is sometimes called a chain tensioner, makes it a lot easier to adjust the chain tension and prevents the rear wheel from moving forward into the dropout.
The second type of horizontal dropouts is technically “semi-horizontal”.
We can find it on old-school road bikes, usually from the 60s and 70s.
While those frames are technically designed for a bicycle with a rear derailleur (note the derailleur hanger), many people use them for single speed conversions because they allow you to slide the axle back and tension the chain without tensioners mimicking the t-pulley of a rear derailleur.
In general, the longer the dropouts, the better because they give you more room to work with.
Since single-speed conversions are pretty popular right now, old road frames with semi-horizontal dropouts tend to have a higher price. Of course, another big factor is the old age and low availability of such frames.
The Downsides of Using Semi-Horizontal Dropouts
Forward-facing, semi-horizontal dropouts are technically not designed for single speed conversion. It just happens that they come with that option.
Subsequently, they have some downsides when used for that task. Those would be:
1. Possible Wheel Slipping
During hard pedaling when sprinting or climbing a hill, the chain exerts a lot of force on the axle. Due to this factor, it’s not uncommon for the wheel to move forward over time.
Hence why it’s recommended to inspect the area frequently and tighten the track nuts if necessary.
Note: Single-speed bikes use axle track nuts with built-in washers to increase the friction between the nut and the dropout. (image below).
Some say that quick-release skewers work too, but more often than not, people report rear wheel slipping when using a quick release for a single speed conversion.
If the nuts get loose as a result of very poor maintenance, the wheel may even drop out and create an accident.
For that reason, it’s highly recommended to get an expert opinion when making a single speed conversion yourself, especially if it’s your first time doing it.
It’s also worth testing the bicycle on “dry land” (away from traffic and pedestrians) before committing to it.
Of course, the wheel may come forward even when the frame has rear-facing dropouts (track ends), but the chances of it slipping out are lower.
2. Lack of Chain Tensioners/Chain Tugs
Most chain tensioners a.k.a. chain tugs that push against the frame to increase the chain tension and secure the rear wheel in place are designed for track frames with rear-facing dropouts.
I’ve heard of people modifying existing ones and even making their own chain tugs designed to work with semi-horizontal, forward-facing dropouts, but more often than not, it’s a custom project with a varying degree of success.
Honestly, I couldn’t find an official chain tug product that claims to work with forward-facing dropouts. This isn’t a surprise since the demand for such a chain tug is too low to justify mass production.
That’s unfortunate because a chain tug increases the safety level of the bicycle and facilitates chain tension adjustment.
3. Retro Look, Ancient geometry
Conversions bind you to retro frames that do not have the tight geometry of a track frame and often look old and beaten.
This property is appealing to many, but some people prefer a modern look.
Also, in some circles, you would be judged for riding a “mixed” bike.
It’s up to you to decide whether any of this matters to you.
The Benefits of Conversions
Even though single-speed conversions aren’t perfect, they come with the positives listed below:
1. Low price
One of the main driving factors behind single-speed conversions is the low price.
If you find a decent road frame for cheap and already have some of the needed tools and components, you could end up with a sweet ride for a low price.
2. The pleasure of building it yourself
A bike assembled by you will likely hold more sentimental value than a genetic unit bought from the local store.
3. Anti-theft properties
A “weird” bike with no gears and an old beaten frame deter thieves. Subsequently, converted bikes could make very decent town beaters.
4. Fender Eyelets
Some of the old road bicycles come with eyelets allowing you to install long fenders with struts without having to do some sort of shenanigans.
5. Easier rear wheel removal
A track frame requires you to first remove the chain from the rear cog before taking out the rear wheel whereas horizontal dropouts allow you to take the wheel right off.
Also, if you’re running a fender on a frame with track ends, you may have to detach it to remove the rear wheel.
This happens because track ends require you to slide the wheel backward and out, and the fender may be restricting that motion.
One of the ways to circumvent this issue or at least soften it is to install quick-release attachments to the struts of the fenders.
Those are technically designed for the front fender. Their purpose is to detach if something gets stuck between the fender and the front wheel.
However, you can buy separate ones too and use them for the rear fender.
They facilitate the removal of the rear wheel by making it possible to quickly “unplug” the rear part of the fender.
Road Frames With Vertical Dropouts Require Chain Tensioners
If the frame has vertical dropouts, then it will require a chain tensioner.
Pulley Chain Tensioners Do Not Work For Fixed Gear Conversions
The chain tensioners replicating the t-pulley of a rear derailleur aren’t suitable for fixed-gear conversions because the stress on the system is too great during skids.
As a consequence, rear derailleurs and dedicated pulley chain tensioners break when used on a fixed-gear.
For that reason, frames with vertical dropouts aren’t suitable for fixed-gear conversions.