Buying guide for best bike derailleurs

Derailleur is the French word for a bicycle gear mechanism that moves the bike chain from one cog or sprocket to another. The derailleur also has a mechanism for taking up the slack in the chain as it moves to smaller cogs.

When should you replace the derailleur on your bike? That’s a judgment call. Derailleur failures normally don’t happen in some kind of catastrophic event. Instead, they gradually get worse, becoming incrementally harder or slower to shift. Other common problems include the chain falling off the largest chainring or cog onto the spokes or falling off the smallest cog and getting stuck between the cassette and frame. If your chain is making noises when you’re shifting, that’s also an indication of trouble.

Many of these problems can be fixed by adjusting the derailleur. Eventually, though, there comes a point when further adjustments won’t be enough to keep things moving smoothly, and you need to install a new derailleur.

A noisy chain is usually the result of the upper derailleur pulley being too close to the cassette. Use the B screw — usually found between the high-limit screw and the low-limit screw on the body of the derailleur.

Key considerations

Front or rear

There are generally two derailleur mechanisms for any multi-speed bike’s gear shifting apparatus: one in the front and the other in the rear. When replacing either of them, it’s important to get compatible mechanisms that work with each other as well as with your model of bike.

• Front: The derailleur for the front cassette (on the crankshaft) on your bicycle isn’t the same as the derailleur on the rear cassette on the wheel. The front derailleur will only have to change between two or possibly three chainrings at the most.
• Rear: The rear derailleur may have to change between eight or nine, and possibly even eleven, cogs on the back wheel. The larger cassette demands a different configuration than the smaller cassette on the front. When you’re selecting a derailleur, make sure you know if it is a front or rear derailleur as they are not interchangeable.

Chain length

The larger the cassettes on your bike and the greater the number of teeth on the rear cogs and front chainrings, the longer the chain you’ll need to accommodate them all. This will affect the derailleur you choose for your bike. Alternately, you can use a bike chain tool to lengthen or shorten your chain.

Type of bike

• Road bike: Road bikes normally have high gearing, with 52/39 chainrings on the crankset. Sometimes there will be a 50/34 chainring on it. Road bikes will seldom have more than two chainrings on the front. The rear cassette, by contrast, will be smaller than the ones ordinarily found on a mountain bike. You must get the correct derailleur for your type of bike.
• Mountain bike: On mountain bikes, the large chainring on the front will be in the 40s or 30s instead of the 50s. Additionally, mountain bikes often have three chainrings on the crankset. Given the differences, mountain bike front derailleurs can’t be used on road bikes and vice versa.

Features

Material

Steel was the bike derailleur material of choice for many years, but advanced manufacturing methods, such as cold forging, especially with aluminum, has reduced the cost and weight of the parts while increasing their strength. Today, derailleurs can be made with a combination of multiple materials, including carbon fiber, aluminum, magnesium, and steel.

Cage length

There are three different cage lengths; short, medium, and long. Long cage lengths are used when there is a large range of teeth between the largest cog on a cassette and the smallest. The greater the range, the longer the cage length will need to be. However, a medium cage length will be sufficient for most bikes. Never change your cage length unless you have a specific reason to do so.

Accessories

• Check your cables. When you’re changing derailleurs, you might as well use the Schwinn SW76193-4 Brake and Derailleur Cable Repair Set to replace the cables while you’re at it.
• Get the proper derailleur hangers. Not all derailleurs come with hangers. You’ll need to use the AUTUT 2pcs Universal Bike Derailleur Hanger to attach them to the bike. There are two hangers in the set along with the instructions.
• Load up on lube. Once you’ve got the new derailleur in place, lube up the chain with Finish Line DRY Teflon Bicycle Chain Lube.
• Make adjustments with a chain tool. You can use Oumers Universal Bike Chain Tool to help you repair the chain while you’re replacing the derailleur. You can remove, splice, and repair chains with one simple tool.

Bike derailleur prices

Inexpensive: Anything under $20 is considered the low price range for derailleurs. At this price, you will normally find rear derailleurs or inexpensive front derailleurs.

Mid-range: From $20 to $80 is the medium price for derailleurs. Most derailleurs, front and back, will be found in this range, from nine to eleven speeds in the rear and up to three in the front. You should expect long-lasting derailleurs of good quality in this price range.

Expensive: Over $80 is where you’ll find the high-end bicycle derailleurs. These will be the high-quality derailleurs for professionals made of the best materials and manufactured to the highest engineering standards.

Tips

• All the major manufacturers agree that cross-chaining — running the chain at extreme angles from front to rear — puts excess friction on the chain and moving parts. Translation: cross-chaining is bad.
• The low-limit screw on the derailleur adjusts how far it can move toward the lowest gear. If the chain is falling off the largest cog (the lowest gear) and getting tangled in the spokes, you can often adjust it to solve the problem with the low-limit screw.
• The high-limit screw does the same thing as the low-limit screw but at the other end of the scale. It adjusts how far the derailleur can move toward the highest gear. If the chain is falling off the smallest cog (the highest gear) and getting caught between the frame and the cassette, use the high-limit screw to adjust the derailleur.
• Slow shifting up and down the cassette can be due to a build-up of debris. Slow shifting can also be caused by the derailleur, hanger, or cassette becoming loose. To troubleshoot, clean the derailleur and chain, then check to ensure that everything is tight and properly aligned.

The numbers etched on the side of the chainring refers to the number of teeth on each chainring. For instance, 50x34 means there are 50 teeth on the large chainring and 34 on the small one.

FAQ

Q. What is a chainring?
A. That is the bicycling term for the toothed sprockets the chain wraps around at the front of the drivetrain on the crankset where the pedals are attached.

Q. What is the chain-wrap capacity of a derailleur, and how is it measured?
A. Chain-wrap capacity refers to the ability of the derailleur to take up the slack in the chain when it moves from one cog to another. Chain-wrap capacity is calculated by taking the number of teeth on the largest cog on the rear wheel and subtracting the number of teeth on the smallest cog of the rear wheel. Do the same thing for the chainrings on the pedals, and then add the two numbers together. The total is the chain-wrap capacity.

Q. Where should the front derailleur be positioned?
A. It should be positioned so the outer cage plate on the derailleur is in line with the outside chainring.