Drivetrain Wear… it happens
Cranks turn, cogs wear, chains stretch; that is the story with all bicycles. But it is often a misunderstood reality of cycling. Everything the chain touches will wear due to friction. The chain too will wear (stretch) causing the teeth on the various cogs (front chainrings, rear cassette, and dérailleur jockey wheels) to sharpen, and the half circle between teeth to widen into a crescent moon. Yet, when it comes time to replace the drivetrain, most riders are unpleasantly surprised by the need and the cost. No matter how much we try to reassure them that this is normal wear-and-tear associated to the sport, most cyclists still regard replacing their drivetrain as a grudge purchase akin to paying your TV licence.
What causes wear (more than normal), what can help reduce it, what symptoms indicate a worn drivetrain, how can you check it, how can you manage it, and how do you resolve it when there is a problem? These are the questions we hope to answer. And even though we write this article from the perspective of a mountain biker, the explanations will apply to road bicycles too.
What causes extra wear and what can help reduce it?
Power. Heavier/bigger riders and stronger riders will put more power through their drivetrain. This will increase friction and stretch, and reduce the life of a drivetrain. Try provide consistent and circular power to the pedals, and use your gears to select the best rhythm for pedalling.
Dirt and Lube. A dirty drivetrain will wear quicker. A clean and lubed drivetrain will last longer. Special, inexpensive chain cleaning devices exist which keep your hands clean and make your chain spotless. Dry Lubes are better for Dry and All-Round conditions, and Wet Lubes are better for Wet Conditions. Also, wet chain lubes look after a chain better than a dry chain lube, but they attract more dirt too, which over time can end up being worse for your drivetrain. Therefore, lazier people (who don’t wash their bicycle enough) should use a dry lube, whereas the fastidious cyclist will get better life out of their drivetrain using a wet chain lube. Remember, after applying a wet lube, rotate the chain a few times and wipe away the excess lube with a clean cloth. Over lubing your chain can attract dirt and clog up the drive train and can be as bad as not lubing.
Trail conditions. Muddy and Dusty trails will cause your chain to clog up with dirt wearing out your drivetrain faster. River crossings can often wash away your chain lube. And long distance rides can use up the lube on your chain leaving it unprotected later on in the ride. The solution is always to try to keep the chain clean and lubed. Carrying a small bottle of lube on the trail can be very effective.
Bad Shifting. Shifting under power, short burst climbing in too heavy a gear, cross chaining, and too many shifts without pedalling are all examples of bad shifting. This will put the chain under unnecessary duress and will stretch the chain and wear the cogs unevenly. Try focus on smooth shifting and pre-emptive gear changes. This will make you faster and improve the life of your drivetrain.
High Pressure Washing. Using a high pressure washer to clean your bike is one of the worst tortures you can put your bicycle through. Not only does it ruin bearings and suspensions, it also strips the chain of all lubrication. High pressure is often used at multi-day stage races. Either try to avoid it, or make sure you thoroughly lube (but not over lube) your chain after it is subjected to the abuse of the wash park.
What symptoms indicate a worn drivetrain?
There are a few things that you might notice when your drivetrain is worn beyond its capabilities. Firstly, visually you will notice that your chain fits loosely to your large front chainring, and the teeth on your cogs will be sharp rather than squared off as they are when new. This includes the teeth on your front chainrings, rear cassette, and dérailleur jockey wheels. If you haven’t noticed these signs, then you may notice slipping when pedalling hard, chainsuck, or ghost shifting (your gears shift erratically, not obeying your shifter but randomly changing at weird times). A noisy drivetrain or a loose slapping chain when descending are also symptoms, but the worst symptom is breaking the chain under normal pedalling.
How can you check your drivetrain wear “scientifically”?
Thankfully there are chain measuring tools you can buy that give a good indication of how worn your drivetrain is. The conundrum is that only the chain is measured to determine the wear of the entire drivetrain. The chain marries the rear cassette when it wears and therefore it is safest to always replace both. The front chain rings and jockey wheels can usually last 2 chain and cassette replacements. The most popular chain measuring tools are the Parktools CC-2, CC-3 and CC-3.2. The CC-3.2 is the current offering from Parktool and it should be available at most bike shops. It measures the drivetrain at 0.5 (50%) and 0.75 (75%). Other chain checkers will show up to the 1.0 (100%) wear mark. What this means for your drivetrain is explained below.
How can you manage your drivetrain and how do you resolve it when there is a problem?
Now here is where we get to the useful stuff, but note that opinions on drivetrain management will differ. I am sure many will argue with our recommendations below and that the component manufacturers will recommend more conservative replacement intervals, but with over 7 years of drivetrain replacement experience in our workshop on bikes with numerous types of components, uses and customers, plus over 50 years of combined bicycle ownership experience, we have a very rounded opinion on what is best for your bike, your wallet and your riding pleasure.
When your chain measures between 0.25 and 0.5, rotate the chain or do nothing. Where you rotate 3 or 4 chains regularly, this is a technique to save money on expensive cassettes, such as the new XX1, by maximising the life of your cassette and chainrings.
When your chain measures between 0.5 and 0.75, you can usually get away with just replacing the chain. This is probably a one-off and the new chain will wear a bit quicker than the original because it isn’t going onto new parts, but it will get more life out of your cassette and chainrings. Then next time you’re ready for a chain replacement, the cassette will probably need replacing too.
When your chain measures between 0.75 and 1.0, you normally replace the chain and cluster. The front chainrings and dérailleur jockey wheels will usually last for 2 chains and cassettes (measured between 0.75 and 1.0) before they too requiring replacement.
Finally, when your chain measures above 1.0, your chain is toast and most likely your drivetrain is completely worn out too. The front chainrings, dérailleur jockey wheels, chain and cassette will require replacement. There are no quick fixes or short cuts. Replace it all, or replace nothing and ride it until it is unbearable or keeps breaking… then replace it all.
After any part on the drivetrain is replaced, it is important to test ride the bike in race simulated conditions especially before any big ride. This also implies that you shouldn’t replace any part on the drivetrain too soon before a race, unless it is critical to do so or the whole drivetrain is replaced. Another important piece of advice is not to cut corners; late replacement or inferior cheaper parts will only lead to unpleasant riding and delayed rather than resolved problems. If you fit a new chain on parts that are too worn, you will notice slipping when pedalling hard and maybe chainsuck too. The slipping can be caused by both a worn out cassette or worn chainrings.
With the wide use of both Triple and Double chainrings, the wear rates on these two systems seem to have there own unique characteristics. Doubles seem to allow for both the small and large ring to wear quite evenly requiring replacement at the same time. Triples are a bit different in that the middle ring usually requires replacement sooner than the big and small ring. Less fit riders will require their small ring to be replaced along with their middle ring, earlier than the big ring.
The costs involved in a drivetrain replacement are as follows: chain from R300, cassette from R450, chainrings from R550, jockey wheels from R200, and labour from R400.
So what route do we recommend? The first important advice is to regularly clean, lube and measure your drivetrain. Our policy is to accept wear-and-tear and to only replace the chain and cassette at the 0.75 measurement for the “first drivetrain” and then replace the entire drivetrain at the 1.0 measurement for the “second drivetrain”. So go buy a chain checker and a chain cleaner for yourself; they’ll save you money, improve your riding experience and provide peace of mind plus a maintenance schedule that works for your pocket.