Ask Matt Archive

Don’t get bent out of shape!   7/19/09

I repair a lot of bikes with rear shifting problems. In many cases the cause of the shifting problem is a bent derailleur hanger. The derailleur hanger is the small part of the frame that the rear derailleur bolts to. With the increasing number of gears on the rear wheel, shifting tolerances are becoming tighter and tighter, which requires high precision in all areas of the drive train. If you are having problems shifting it may be that your rear derailleur hanger is bent or broken. It is important that the hanger is straight and parallel to the cogs on the rear wheel. If it is not, then it won’t line up with the gears. If that is the case, then no matter what you do with the cable, you won’t achieve smooth shifting action.

When most bike frames were made of steel, there was no need for replaceable derailleur hangers. Steel can be bent safely many times before it breaks, so bent hangers could easily be bent back straight. When aluminum frames first became popular they did not have a replaceable hanger. This led to a problem because aluminum does not stand up well to being bent many times. With aluminum, even just one good bend will break it. Early aluminum frame owners were not happy when one bad crash would cause a broken hanger and they were left with scrap metal instead of a bike. Hence, the replaceable hanger was born. Now instead of scrapping the bike just the broken hanger can be replaced.

There are many ways a derailleur hanger can get bent. Crashing is the most obvious way. If you see any marks on the derailleur after a crash, that could be a sign that the derailleur hit the ground and possibly bent the hanger. Other less obvious ways a hanger could get bent are by laying the bike down on the drive train side or by loading the bike in the trunk of a car. If you don’t have a bike rack, be very careful when putting your bike in the trunk so as not to bend your hanger. Even if you have a brand new bike, don’t assume your hanger is straight. Having built thousands of bikes, I have seen plenty of hangers that are bent right out of the box.

If you have a bent hanger there are two ways the issue can be corrected. One being to bend the hanger back straight and the other is to replace the hanger. A Derailleur Alignment Gauge (DAG) can be used to bend the hanger back straight. This is a fairly straight forward procedure but best left to your mechanic. As I mentioned before, aluminum can’t always be bent back safely. If the hanger can not be bent back straight and you have a replaceable derailleur hanger (many modern bikes do) replacing it is your only option. Once you replace it, it is best to double check the new one to make sure it is straight also.

If you have questions please feel free to contact me and I will answer them.


What to do if you break your chain?    5/27/09

What to do if you break your chain? Have you ever been on the trail having a great ride and then you try to shift and the chain breaks? This is what you need to do to keep the ride going and the mojo flowing. These methods also work if you are on a road bike so keep reading.

There are two major manufacturers (SRAM and Shimano) of chains in the biking world. Yes there are others, but I am going to concentrate on Shimano and SRAM. They are the most popular and chances are you have one or the other on your bike.

First, you have to know or figure out what kind of chain you have before you hit the trail. The name of the manufacturer should be on the chain. If you have a Shimano chain, you will need Shimano chain replacement pins. If you have a SRAM chain, you will need a SRAM Powerlink.  Unless you are riding a unicycle, you have a chain, so you should have a chain tool. You may already have one on the mini tool in your seat bag. Now that you know what kind of chain is on your bike, and have the appropriate tools and spare parts available you will be prepared to fix a broken chain while on the ride. Below are instructions for fixing the chain, as well as important information on what needs to be done afterwards:

Instructions for SRAM owners: The first step is to remove the broken links with a chain tool. You want to remove enough links to end up with the inner link exposed on both ends of the chain. Now install the Powerlink. Each half of the Powerlink will attach to the end of the chain. Then connect the two halves of the Powerlink to each other.

Instructions for Shimano owners: The first step is to remove the damaged links. Remove the links so there is an inner link on one end and an outer link on the other. Use the Shimano replacement link to join the two ends together. Insert the smooth end first. You will use the chain tool to push the pin through the hole in the links. As you push you will feel a series of tight and loose points. Watch as you push the pin so you don't push it too far. Once you have the chain joined, break off the back half of the pin.

No matter what chain you have, now that the chain is shorter there are two things you need to keep in mind. First, don't shift into the big ring/big cog combo. The chain will be too short to go into this gear. If you do this then there is a very high risk of damage to at least the derailleur. Second, go buy a new chain (hopefully from me) and trim it to the correct length.

If you have questions please feel free to contact me and I will answer them.

what's a snake bite?    3/22/09

What is a snake bite in the cycling world? A snake bite is a type of hole in your tube caused by an impact with a stationary object (i.e. curb, pothole). The tube is pinched in between object and rim and results in two small holes in the tube that resemble a snake bite. The best/easiest way to address this issue while you are out on the ride is to replace the tube with a new one. You may not want to patch the tube on the ride because there might be a seam near the holes preventing a perfect seal with a patch. Once you get home, you can attempt to patch the snake bite with a large patch that covers both holes. Then, check to make sure the patch is airtight. You can do this by letting the glue of the patch cure, inflate the tube and submerge it underwater. Bubbling would indicate a leak and you should trash that tube.


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