| What is "Chain Stretch"? When do I need to change my chain? --->Ride it 'till it breaks theory --->New Chain Before the Old One Causes Damage theory Compatibility- choosing a chain Sizing & cutting to length Installing the chain Fixing a broken chain trailside. What is chain stretch? "Chain Stretch" is the gradual lengthening of a chain over time. In fact, the chain is not actually stretching, but due to friction, the connections between links slowly wear and become looser which adds to the overall length of the chain. The cogs on the bike can tolerate a certain amount of this, but if a chain is run too long, the teeth on the cogs will start to wear so that they mesh with the new chain length rather than the standard chain link spacing. Chain and cog combinations that wear together like this will typically work fine until such a time as one of the components needs to be replaced. i.e. if you want to change your chain or put on a new cassette to change your gear ratio you will need to replace the whole system. Problems cause by chain stretch usually present when you break a chain and replace it. The new chain will tend to skip off of the cogs, especially the smaller ones. Depending on the amount of stretch that occurred before you changed the chain, you may be able to get away with not changing your big ring, and sometimes even your granny ring if you don't use it much, but your cassette will need to go. Other than knowing symptomatically that your cogs are worn, you can often notice a shark-toothed look to the teeth that is caused by one side of each tooth being worn more than the other. |
|
| When do I need to change my chain? There are two schools of thought on this. The one that you will get from most shops is that you want to change the chain often enough so that it wont destroy your cogs. The second school says, just ride the chain until it breaks, and just replace what you need to then. I will examine both strategies below, both have their advantages. Ride it 'till it breaks theory This theory takes the bet that you can ride the bike long enough without breaking the chain, that the cash you save in not buying new chains will outweigh the cash you have to spend on all Chainrings and cogs when the time comes. This is often the case with road bikes, and even on mountain bikes if you run a high quality chain and make sure you are good about shifting before climbs so that you are not forcing shifts under high torque. The drawback is that you wont be able to swap out rear wheels unless you swap out the cassette as well. So if you have race wheels and training wheels, or race in races with a wheel van, this will be a problem. Personally I only use this theory if I miss a chain change. Once the damage is done, you can't undo it, so you may as well go with it. New Chain Before the Old One Causes Damage theory If you have multiple sets of wheels, like to change your gear ratios, or want the ability to take a spare wheel on the fly, you must use this approach. So, how do you know when it is time to change your chain. The best way is to purchase a chain checker. Park has some inexpensive chain checkers that are worth their weight in gold. A chain checker is a tool that has two little pins that fit between the links of your chain, and then widen so that they can measure the length of that section of chain. Depending on that length it will tell you that the chain is either "new","good", or "needs to be replaced". If you don't want to buy the tool, you can also measure a section of the chain with a ruler to determine how stretched it is. (I will have to look up what you are looking for here and post it later). This method works, but it introduces some human error that I don't want to mess with. Some people will also give you mileage or time estimates like: "Change a MTB chain every year","Every 3000 miles on a roadbike" etc.etc. I find that people throw around a lot of numbers like this, but the stretch on the chain is dependant not only on hours ridden, but also on the quality of the chain, the conditions (muddy or dry), and probably even the type of lubricant you use. So it is far better to use a chain checker or ruler than rules of thumb. Tip: SRAM chains use a "power link" that allows you to take a chain off and put it back on without weakening it. Other chains can be put back together using a "Quick Link". When you replace a chain, save the old one until after you have had a few rides on the new one. In the event that you accidentally left the old one on too long you will have all sorts of problems with the new one that can be resolved simply by putting the old one back on. This will allow you to replace the whole setup whenever you are good and ready. |
|
| Compatibility- choosing a chain All the major brands of chains are compatible with Rings, Cogs, and derailleurs from the other brands, provided you have the right width. i.e. If you have a nine speed setup, make sure you have a 9 speed chain. A chain too wide will not be able to settle in between the cogs, and one too narrow has the potential of jamming in between the Chainrings. So, determine how many cogs are on your cassette, and use the appropriate chain. (i.e. 8 cogs in the rear = 8 Speed chain) |
|
| Sizing and cutting to length
You will hear a number of methods for sizing a chain, hear are the basics. The third one is the best one, so I will talk about it the most. 1. Cut the chain to the same number of links as the one you took off. This is fine if you still have the chain, and it was sized correctly to start with 2.String the chain around the smallest cogs and through the derailleurs, Then cut the chain to a length so that the chain just barely clears from rubbing on itself where is wraps under the rear derailleur. This works ok, but can lead to making the chain too short which could damage your rear derailleur when you shift into the big-big combination. 3. the best one Wrap the chain around the largest cog in both the front and back without running it through the derailleurs. Pull the chain tight, and determine the spot where the chain comes together. Once you have this spot make the chain two or three links longer depending on which link you need to attach the ends correctly. Once you have the length you can cut the chain, string it through the derailleurs and connect it. If you get the chain rub as described in the second option, it can be removed by adjusting the B-Screw tension on the rear derailleur. (Note: The B-screw is the small screw that pushes against the derailleur hanger. When you tighten it down it pulls the derailluer towards the back of the bike which will take some slack out of the chain. It should be noted, that this is not the purpose of the B-screw, but a side effect. If, in order to get you chain to stop rubbing you need to tighten the B-screw so much that you lose crispness in your shifting, you may want to check that your derailleur has a high enough tooth capacity to accomidate the gear ratio you are running.)  Chain sized by using large rings and adding a link pair |
|