Yes, they do! Although technically what the chains are doing is not “stretching”, they do wear out over time, which in turn affects the performance of other parts of your bike.
In fact, your bike’s chain wears out a little every time you take your bike out for a ride. Each time you pedal, the chain converts your leg power into rotations for the rear wheel. This pressure causes the chain to wear out.
The time it takes for your bicycle chain to get worn depends on a few factors: how it’s used, how well it’s maintained, and the quality of the chain itself.
To learn more about the mechanics behind chain wear and how to tell when it needs replacing, read on.
Why Bike Chains Stretch
To understand the process through which bike chains wear out, it’s important first to understand the chain’s parts. The individual pieces that make up a chain are the pin, bushing, outer plates, roller, and inner plates. In recent times, the bushing in the chain is combined with the inner link plates, and they hold the roller, which is circular.
Every chain link is connected with the next one, alternating between the inner and outer plate. One segment of chain containing an inner plate and an outer plate is normally thought of as one whole chain link.
The “pitch” of a chain refers to the space between each pin. On multi-speed, “derailleur” type bikes, the is usually 0.5 inches between the pins. (NB: Here, we are not referring to the workings of single-speed bikes).
Chain stretching occurs when the bushings wear with the chain pins. With time, the bushings’ inner diameter increases, causing the pins to groove out. While the actual length of the chain remains unchanged, the pitch does not stay the same length.
Ensuring the maintenance of your bike’s chain is not only a way to prolong the life of the chain but of your bike’s whole drive train. This is because your bike chain is very close to the ground and is exposed to harmful elements every time you take it out for a ride.
When to Replace a Worn Chain?
Bicycles certainly have a simple mechanism compared to other vehicles. However, it’s because of their simplicity that they’re prone to malfunctioning if even one part is damaged.
The drivetrain of a bike, specifically the rear cassette and the front chain ring, are designed to exactly fit the chain pitch. If there is even a small deviation, you’ll feel a loss of maneuverability. And the longer it goes untreated, the higher the chances of the chain slipping.
Simply a 1% increase to the bike’s pitch, the standard measure of which is about 0.5 inches (or 12.7mm), indicates that your bike’s chain has worn out or stretched. That’s when it’s time to replace it.
When your bike’s chain is stretched, the teeth on the cogs appear to be sharper, which means they are getting shorn away. Excessive wear results in a chain that slips or a rider who faces difficulty in shifting gears.
Thankfully, most chains come with a quick link, making it easy to replace them.
Is Chain Stretch Bad?
It most definitely is. Chain stretch not only decreases the efficiency of your bike by damaging drivetrain components but also makes it difficult to shift gears. Not to mention, being stretched weakens a bike chain, and that makes it much more prone to breakage.
Furthermore, you can save hundreds of dollars by catching the depreciation of your bike’s chain before it begins to damage other components of your bike. New chains, with 0.5-inch pitches, are intended to sit snugly inside the cog.
When the pitch will grow, the chain rolls will go higher up, resulting in faster and more pronounced cog wear. The higher the amount of chain wear, therefore, the higher the chances of the chain skipping over the cog’s top.
Putting a worn-out old chain on a recently bought cassette is a sure-fire way to ensure that the cassette wears out faster. That’s why it’s important to replace the chain before it gets a chance to wear out completely: the gears on both the chainring and cassette will be much more durable that way.
It can also cause your chin to slip right off the cassette and damage that fancy paint job you have on your bike.
How to Measure Chain Wear?
The only way to know if you need a new chain is to measure it at regular intervals. Measuring the wear on a bike’s chain is the first step in preventing damage to your bike’s entire drivetrain. So, measuring chain wear should be a part of your bicycle maintenance routine, along with applying chain lube.
Thankfully, chain checking tools (available at bike shops) are quite inexpensive, should you choose to buy a chain checker. Some people even use traditional tape measures and rulers.
This is what a chain checker looks like:
As you can see, a chain tool comes with two slots. The slots of the chain gauge fit into the gaps or the pitches of your bike chain links. If it doesn’t fit snugly into the chain links, that means you have to replace your chain links.
Some chain checkers come with a measurement marker on their bodies so that you’re not making shots in the dark.
If you want to use a ruler instead, that’s also possible. Lay your bicycle’s chain out and get a 12-inch ruler to measure the chain length. If the chain measures exactly 12 inches from the middle of one pin to the middle of another across 12 links, you should be good to go.
However, as mentioned before, if there is even a 1% discrepancy, that’s a sign that the chain is worn and you need a new one. So, if your measurement shows past 12, 1/16”, you know what to do.
And of course, if the measurement is past 12, 1/8”, that’s a severely worn chain. At that stage, you don’t just need a new chain, but a cassette as well.
Bike chain stretch is one of the things no one really warns you about before you get your first bike. But, we hope this article has helped you identify the problem before it grows any bigger.
If you have any worries about it and don’t feel like checking it yourself your local bike shop can check it for you in about 10 seconds!
Have fun out there!