Derailleurs - Helpful advice to keep your bike shifting happily

I love derailleurs. Derailleur adjustments are my favorite part of a bike tune-up. Without derailleurs, your bike would be a single-speed; and nothing against single-speeders, but I think that just makes for a sad time. 

An improperly adjusted derailleur can ruin a ride, or stop a ride from even happening on what is probably the most beautiful day of the week. Because, let's be real, inconvenient things seem to have a knack for occurring on the best days of the week.

The purpose of this blog is to get you familiar with derailleurs so, should you find yourself at a moment in time where a shop mechanic is not available to help you out, you can get your bike shifting again (or at least well enough to get yourself home).

Even though there are mountain bike and road bike specific derailleurs, derailleurs usually all function in the same way. Varying designs may make derailleurs look unfamiliar between component brands, but if you get familiar with the general parts, you'll start to notice they all actually seem fairly similar.

Most Rear Derailleurs will have the following:

View fullsize

• Mounting Bolt - this attaches the derailleur to the bicycle frame. 
• Low Limit Screw - this limits the chain from shifting off of your largest cog and into your rear wheel
• High Limit Screw - adjusted to allow the chain to shift into the smallest cog, center chain placement relative to the smallest cog, and prevent chain from falling off and into the frame of the bicycle
• Cable Anchor Bolt - this is the bolt responsible for keeping the shift cable in place, it also is responsible for holding the cable tension.
• Derailleur Cage & Pulleys - Rear derailleurs contain two pulleys. A Tension pulley keeps tension on the chain as it moves through the drivetrain, and the Guide Pulley stays true to its name and guides the chain from cog to cog as you shift
• Barrel Adjuster - Sometimes found on the rear derailleur. If it's not on the rear derailleur, there will most likely be one placed on the rear shifter or in the shift housing. This is used for getting that last bit of cable tension adjustment that just isn't possible at the cable anchor bolt. Think of it as fine tuning your shift cable tension.
• B-Tension Screw - this screw is responsible for adjusting the tension the derailleur is placing on the chain; there are specific guidelines to follow for this adjustment based off of your type of rear derailleur. Guidelines can usually be found on manufacturer's websites (or you can ask one of us here at the shop) :)

Most front derailleurs will have these parts:

View fullsize

• Mounting Bolt - this attaches the derailleur to the bicycle frame. Height and angle adjustments occur here to properly line up the derailleur with you bike's chainrings
• Low Limit Screw - this limits the chain from shifting off of your little chainring and falling into your frame.
• High Limit Screw - adjusted to allow the chain to shift into the largest chainring without letting the chain overshift and falling off of the big chainring
• Cable Anchor Bolt - this is the bolt responsible for keeping the shift cable in place, it also is responsible for holding the cable tension.
• Derailleur Cage - There are Inner and Outer parts to this; the Inner Cage sits closer to the frame of the bicycle, the Outer Cage sits further away from the bicycle. The cage is responsible for physically moving the chain when shifting is engaged
• Barrel Adjuster - Not usually seen physically on the front derailleur of road bikes, but sometimes placed in the housing of the front shift cable or somewhere on the downtube of the frame. On mountain and hybrid bikes, it can usually be found on the front shifter. This is used for getting that last bit of cable tension adjustment that just isn't possible at the cable anchor bolt. Think of it as fine tuning your shift cable tension.

It probably seems like there are a lot of parts to try and remember. And you might be thinking, "There's no way I'll remember all of these things. How is this supposed to help me work on my bike?"

It will take a few times of trial and error to get derailleur adjustments right, but understanding some of the scenarios in which your derailleur isn't working will help you greatly.
 

Things that will cause shifting issues:

View fullsize

• Cable Tension (pobably the most observed issue):
  • Cable is either too loose or too tight
  • If your cable is not shifting into the big chainring in the front, or the largest cogs of your cassette (on the rear wheel), this can be an indicator that you do not have enough cable tension
    • this can be adjusted with the barrel adjuster and/or physically pulling the cable tighter at the cable anchor bolt
      • when adjusting the barrel adjuster, you'll know you are turning it to tighten the the cable by seeing the inner plastic piece emerging from the outer dial
  • If your cable is not shifting down into your little ring in the front, or into your smaller cogs of your cassette, this can be an indication that your cable tension is too high
    • this can be adjusted in the same ways as if your cable tension is too loose, except at the cable anchor bolt you will be letting in some slack in the cable tension, OR at the barrel adjuster you'll be turning the dial so the inner plastic piece winds back into the outer dial.
• Limit Screws are not properly adjusted:
  • The High & Low limit screws prevent the derailleur from shifting the chain off the of the drivetrain and into the frame/wheel, or causing the chain to overshift off of the big chainring
  • When the limits are not adjusted properly what is usually seen is chain-dropping or the derailleurs are unable to shift the chain into the large chainring/cogs.
• Derailleur Hanger is Bent (rear derailleur):
  • The derailleur hanger is the piece that holds the rear derailleur to the bicycle frame. It is meant to fail first in the case of a crash to help prevent bending the derailleur
  • If this is bent, the derailleur will be out of proper adjustment/alignment in relation to the cassette
  • A bent derailleur is usually good for one session of bending it back (best done by a bicycle technician)
    • If you're a mountain biker, taking an extra derailleur hanger (specific to your bicycle) out on the trails with you is usually a smart idea. It's more likely that you'll damage/bend a derailleur hanger on the trails than on the road; just more things in the trail to get flung up and hit your bike, as well as more opportunities to dump your bike if you're feeling rambunctious
• B-Tension not properly adjusted:
  • because the B-Tension is so specific to the drivetrain, this should be already set up for you when you purchase a bike. However, sometimes things can happen, and the tension can come undone. Just a good thing to know if you cannot find issue with anything else wrong with your derailleur setup
• Derailleur itself is damaged or bent:
  • Newer derailleurs have become burlier, and the mountain bike derailleurs seem to hold up to a decent amount of beating. However, a crash can ruin a derailleur. Front derailleurs can also become damaged or bent from shifting too hard into the big chainring; the cages will become splayed and then the limits get out of adjustment

Running through these scenarios as a checklist can help you (in most circumstances) figure out if and what is wrong with your derailleur and whether or not you want to attempt fixing it yourself, or have your friendly local bicycle technician run through and discus the issue with you and your bike.

I've made these drawings and descriptions into blog because when I first began working on bikes and completing these adjustments, I felt lost. I wished for a helpful picture to keep handy if I couldn't remember what screw did what or why the cable tension wasn't cooperating with me. I didn't always love doing derailleur adjustments. It took me a while to figure out the problem-solving matrix, and understand scenarios that can make derailleurs do crazy things. But now that I know these adjustments, I want to help others understand them and not feel nervous when they realize their bike isn't shifting properly all of a sudden. I hope that this is a helpful guide to anyone that reads it. Also, keep an eye out for our maintenance clinics by checking out our event page! We offer co-ed and women's only clinics!

- Kelly

*All pictures are by Kelly Paduch and may not be used without her express permission*