Ask the Experts

Q:  "My bike seemed to be adjusted fine and then all of a sudden, while I was out on a ride, my rear derailleur shifted into my spokes. Now I need a new rear derailleur, new chain, something called a derailleur hanger and a new rear wheel. How does this happen?"

 A:  This is a common repair but one that is mostly avoidable if you know what to look for on 

Photo 1 - What you should see - a nice straight derailleur and chain.

your bike.

Periodically, check the alignment of your rear derailleur. A rear derailleur is perhaps the most delicate and precise component on your bike, and as such, needs to be in near perfect alignment to work properly.

Photo 2 - What you don't want to see - a bent derailleur waiting to cause havok on your drivetrain.

When you look at your bike from the back, you should see the chain flowing nicely off the rear gears, or "cogs" and into the derailleur. There should be no bend in the rear derailleur (see Photo 1).

If, however, you see a bend in the rear derailleur, such as in Photo 2, you could have an issue where the derailleur overshifts into the spokes and causes extensive drivetrain and rear wheel damage.

So, how does this happen? Most modern bicycles come equipped with a replaceable rear derailleur hanger (see Photo 3). A derailleur hanger is designed to bend or break in the event of an accident so that the bike frame is not damaged or destroyed. There are over 100 different types, so if you need to replace yours, we'll need to know the

Photo 3 - Just one example of the many styles of replacable rear derailleur hangers.

make, model and model year of your bike if you do not have the remains of the part.

But, you don't have to have an accident to bend the derailleur hanger.  Dropping the bike on the derailleur, transporting the bike in the back of a car instead of using a bike rack, and shifting your bike under load can all bend the derailleur hanger and affect the alignment of the derailleur.

The way to solve this issue is to use a special tool called a rear derailleur alignment guide and bend the derailleur hanger back into the correct plane with the rear cogs.  This is a simple procedure and when we perform the repair we not only check the alignment of the derailleur, but we also readjust the rear derailleur itself.

Before your ride, take a second and glance at your rear derailleur.  Is it straight?  Happy riding!  If it's bent, save yourself an expensive repair bill and get the derailleur hanger realigned and your derailleur readjusted.

Our "Ask the Experts" column is a monthly feature that answers questions that we receive in our general e-mail inbox.  Have a question for us?  Send it to us at info@thebicyclewheel.net.  Each month we pick a question that we think is timely and relevant to our readers.