What Happens If You Don’t Replace a Worn Drivetrain? 


If you want to enjoy top performance and get the best value from your bike, you’ll need to keep your drivetrain in good shape. Sometimes, that means replacing a worn drivetrain.

If you don’t replace a worn drivetrain, your drivetrain can begin producing unpleasant noises, and your chain might jam or suck backwards. At best, performance declines, and at worst, these issues can cause crashes and injury. 

On the other hand, following a solid replacement schedule will keep your drivetrain running smoothly and safely. There isn’t a single magic number for drivetrain replacement, so you need to be diligent and check your parts regularly. Let’s see what you need to replace and what to watch for to understand when the time has come.

Which components of a worn drivetrain can damage your bike?

The chain is the crucial point of failure that can directly damage your bike when something happens to it. However, it’s not the only part of a worn drivetrain to keep in mind. If the parts that the chain interacts with are worn out, they can contribute to more rapid wear and tear on the chain. 

In most cases, drivetrain operation is self-contained. That is to say, worn chains and sprockets usually manifest as worse performance without harming anything but the other parts of the drivetrain. However, drivetrain issues can cause jamming and contribute to crashes

Is it unsafe not to replace worn drivetrain parts on time?

There are a variety of potential consequences to not replacing worn drivetrain parts, and these can be hazardous. In extreme cases of wear and tear, for instance, the chain can break. This isn’t the most likely event, but it can happen and harm you and your bike in the process.

More common consequences of not replacing worn drivetrain parts include the chain jamming or sucking backward. In either case, these can jolt you to a sudden stop or throw you off balance, creating a serious risk of crashing. 

Besides safety concerns, though, there are other consequences to not replacing drivetrain parts. For one, you’ll notice a steady decline in performance and more awkward transitions when shifting. Worn drivetrain parts also begin to produce increasingly unpleasant noises as you ride. 

Which parts of the drivetrain do you need to replace?

It’s possible for any part of the drivetrain to need replacement. However, the part of the drivetrain that suffers the most wear and tear is the chain, and it’s the part that needs the most routine replacement. The other parts of the drivetrain that need the most regular replacement are the parts that the chain transfers motion to directly, namely the chainrings and sprockets. 

Wear and tear is an inherent part of riding a bike, and it happens to your drivetrain with every revolution of the wheels. As the metal parts rub against each other, tiny shards of metal break off the chain and sprockets and the parts deform ever so slightly. 

Proper lubrication and regular chain replacement will partly shield the parts of your drivetrain from this effect and extend the life of your entire drivetrain. You can track wear and tear with chain wear indicator that measures chain stretch (it’s a pretty inexpensive tool you can buy on Amazon here).

Mind you, chain stretch doesn’t mean the chain is literally stretching. Rather, the grooves within the chain elongate with time, and this warps the chain and the chainrings. When chain stretch reaches .75%, you need to at least replace your chains. By the time you reach 1% chain stretch, it’s necessary to replace the cassette as well. 

How often do you need to replace the chain and sprocket?

There’s a wide range of possible replacement times for the chain and sprocket. Your chain could need replacement in under 1,000 miles if you maintain it poorly. However, a well-maintained chain can last up to 2,000-3,000 miles of riding before you need to replace it. 

Besides maintenance, riding conditions make a significant difference. That 2,000-3,000 figure assumes dry, clean areas where less dust and moisture will get into the drivetrain. Particularly humid, dusty conditions can reduce that figure to 1,000-1,500 miles. In both cases, there’s enough room for error that you should be diligent about checking for chain stretch. 

If you’re consistent about replacing your chains close to .75% chain stretch, you won’t have to replace your sprocket immediately. Instead, you can replace your chains once or twice first. Once your sprocket needs to be replaced, or the third time you replace your chains, you can replace them together. 

It’s unlikely that a sprocket will remain serviceable once you’ve run through more than two chains. On that note, you’ll also need to replace the chains any time that you replace the sprockets

Do you need to replace the sprockets and chain at the same time? If so, why? 

The issue of replacing sprockets and chains at the same time is nuanced. For instance, you can sometimes replace chains without replacing the sprockets. However, any time that you replace the sprockets, you should also replace the chain. There are two reasons for this; worn-out parts cause faster wear on new parts, and chains are cheaper than sprockets

When you have a new drivetrain, both the chain and sprockets are fresh and interlock correctly. As they wear, they wear in proportion to each other. If you have one worn part and one new part, the new part will wear relatively faster. 

Replacing your chain as soon as you reach .75% chain stretch while keeping the sprocket sounds inefficient at first. After all, your new chain will wear out faster. However, the difference in price means that it’s acceptable to wear out a new chain if it means getting more life out of your sprockets

However, it’s never acceptable to do the reverse. If you run a worn chain on a new sprocket, it’ll wear down the more expensive, complex part and force you to replace it sooner. Even if your chain still has life in it, you should always get an entirely new chain to complement a new sprocket

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When it comes to Cycling to Work, SAM IS THE MAN because he doesn't just talk the talk, but he also walks the walk - or rides the ride, to be more precise... Come, pedal with me and be a HERO!

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