When you think of your bike’s shifting, you probably think of the chain, cassette, and the shifters themselves. But none of that would lead to anything without the help of the derailleur.
If you do get in an accident that leads to a broken derailleur, you’ll likely be looking at spending upwards of $100 to replace it. The derailleur itself will cost around $50 and the hangar that holds it will cost around $15. If you bring it into a shop, you’ll also need to pay for the labor, which can be anywhere from $40-$60 depending on your location. (Source).
It’s more common for just the hangar to break, especially for mountain bikes, which is why a lot of new bikes will come with a spare derailleur hanger. This can be simple to replace on your own, but you could also bring it right to the bike shop and have them do it for you since you already have the part.
Which Leads to The Question: What Is a Bike Derailleur?
Before we jump into the maintenance and replacement of derailleurs, it’s helpful to understand their function on the bike.
A bike can have one or two derailleurs: the front derailleur and the rear derailleur. Both of them serve as systems to guide the chain to different gears. All bikes that have shifting will at least have a rear derailleur, so we’ll start with that one. (All technical information is courtesy of Park Tool, with sources linked below.)
As it sounds, the rear derailleur controls the shifting on the back sprocket. While there are quite a few different styles and models, they all share the same general design and provide the same function. They are secured to the bike with a mounting bolt to the frame’s derailleur hanger. There is an upper pivot and a lower pivot which connects by a linkage system to form a parallelogram (Source).
In addition to the pivots, the rear derailleur will have two pulleys: the lower pulley and the upper pulley. The lower pulley or “T” pulley (short for tension) pulls backward and gives tension to the lower portion of the chain. The upper pull or “G” pulley (short for guide) helps to guide the chain into the correct sprockets.
Most bikes will have mechanical derailleurs, which have a cable secured by a pinch bolt. Pulling the cable (by using the shifters) moves the cage inwards while a return spring moves the derailleur in the opposite direction once the cable is released. There are also electrical systems (called electronic shifting) that eliminate the need for a cable and use a small motor paired with Bluetooth instead.
Bikes that have more than one chainring in the front will have a front derailleur. Like rear derailleurs, these have a cage that forms a box around the chain which is attached to a parallelogram-shaped linkage system. Mechanical derailleurs utilize cables to move the linkage system, which then guides the chain.
For front derailleurs, shifting can only occur if the rider is pedaling. To shift outward, the chain is flexed to the right and starts to rise up due to the pedaling. The chain stays on the right track with the help of shift ramps and other modern features. (Source)
Shifting inward works in a similar way. The cage pushes the chain from behind and continues to push in until the chain essentially “falls off” the larger ring. The smaller ring then catches and engages the chain.
If your derailleur isn’t properly indexed, you may end up dropping your chain during the shifting process. Because chains stretch over time (and due to repeated use), you’ll need to periodically adjust your cables.
On a side note, find out How to Choose the Best Cassette for Triathlon? What You Should Know!
Do All Bikes Have a Derailleur?
No, not all bikes will have a derailleur because they only use one speed. These bikes are often called single-speed bikes, fixies, or fixed geared bikes. These types of bikes were incredibly popular about a decade ago, though they’re a bit less common now. They are typically used by people who are looking to just commute around and don’t want to deal with the (perceived) hassle of shifting.
A fixed-gear bike doesn’t have a flywheel. This means that you’re constantly pedaling as you move, keeping your legs permanently engaged.
These terms just started getting used so casually that they got confused with the more common single-speed bikes. A single-speed bike has only one chainring in the front and just one rear sprocket, making it a one gear ratio. These bikes will still have a flywheel, which allows for coasting while biking (Source).
The simplicity of these bikes is their greatest appeal, especially for casual riders. They are also far less expensive than most road bikes which make them accessible to more people. It can also be a great choice for people who bike commute in the winter because there are fewer components to worry about. Another popular single-speed bike category is BMX. These bikes are small and mostly used for pump tracks, tricks, and hitting the skatepark.
How Often Should You Replace Your Derailleur?
In general, the derailleur should last almost as long as the bike itself, so you shouldn’t need to replace it unless you get in an accident and it breaks. Certain components of it will likely need to be replaced over time, though, especially the cables and jockey wheels.
The jockey wheels serve a super important role but are often overlooked. Remember the “G” and “T” pulleys from the rear derailleur? Those are the jockey wheels. If your bike has been well-maintained, a good jockey wheel can last for years, but it’ll need to be replaced eventually.
If the teeth on your jockey wheels are heavily worn, it will negatively impact your shifting and can ultimately lead to more costly repairs in the future (Source).
Keep an ear open for any noises coming from the derailleur as this may be a sign that the jockey wheels have worn out. You can also visually inspect them for signs of wear.
Can You Use a Bike without A Derailleur?
Technically, yes, you can ride your bike without a derailleur. This would essentially turn it into a single-speed bike. If you find yourself on a ride with a broken derailleur or hangar, you can do some quick maintenance to get moving again without it. All you’ll need is chain tool, Allan keys, and (preferably) a quick link. (Source)
If you have a chain tool, you can simply remove the chain. Otherwise, you’ll need to break it off. Next, you can remove the derailleur. Once that’s off, you’ll be able to find the gear that allows for your chain to stay straight (this will usually be the middle gear).
Now you can reattach the chain using either your chain tool or a quick link. Of course, this setup won’t be as strong as your previous (unbroken) setup, so be careful with applying too much pressure as you pedal back home.
Derailleurs serve a vital function for bikes with multiple gears, but they aren’t required for all bikes. Just keep in mind that removing the derailleur means removing the ability to change gears, which can make climbing hills or pedaling into the wind even more challenging.