There’s never a good time for your chain to skip, but it almost always comes at the wrong time, typically under a load when standing or climbing. It can be a subtle click, or a body dropping tremor. It takes you by surprise, and just for a moment, you’re not exactly sure what happened.
Chain Skip Will Happen Again
It can happen once, or sound like a series of pops in your drivetrain. The harbinger of bad news, it’s a sure bet it will happen again and again, getting worse as you add the miles.
Some cyclists confuse chain skip with shifting issues caused by poor tension on the cable, causing the chain to miss its intended target, skips, and then grabs hold of consecutive teeth as it was supposed to do the first time. This type of skip can be easily fixed by using the barrel adjuster to add tension to the cable. It’s a shifting issue, not a chain skip issue.
True chain skip happens when one component of a drive train has just been replaced, or the drive train has been used so much that the chain skips over the top edge of the cog teeth. The most common skip happens when you begin a climb in high gears, stand up on the pedals, and apply torque to the chain. The chain rides up the gear and slips up and over the tooth. It might skip one tooth or several before hooking up again.
Chain skip usually occurs in your favorite gear or gears, as these are the gears you use more than the others, and therefore wear out first.
Blaming skip on a stretched chain is misleading. Chains get longer when the holes in the links become elongated where pins pass through. Pins also wear to a certain extent, because pins do not have bearings that serve to reduce metal to metal friction.
Every time you ride your bike, your chain gets longer. It might be minimal, but it’s there in theory. New chains typically measure exactly one pin for every half inch. A chain that has thousands of miles ridden on it should have pins that match up on every half inch mark, but by the time you get to twelve inches the twenty-fourth pin will likely be past that marker. How much it is past will indicate chain wear and determine if you require a new chain all together.
As a chain elongates it wears the leading, top edge off of the cogs, because it doesn’t match up with them. Worn out gears look like shark fins or hook slightly on the worn edge, giving the gear the appearance of a table saw blade. In other words, the gears conform to the chain, resulting in the shark tooth sawblade appearance. Therefore, if you replace your chain regularly, gears shouldn’t wear out at a significant rate.
You’ve probably heard the term “chain suck.” It is also a product of worn chains and gears. Chain suck is a condition where worn chains fail to disengage from the worn gears. The chain rides back up the gear. It’s more common on mountain bikes, often locking up the gear. It’s characterized by a noisy clatter on road bikes, when the chain rides up and then disengages with a noisy clatter. If you hear it consistently, you will likely be having chain skip issues to accompany it.
What Causes Chains to Wear
Chain wear is caused almost exclusively by road grit that enters the chain when it’s oily. Grit adheres to the oil. It’s the ugly black stuff that gets on your calf, causing the badge of honor, the chain ring tattoo. The black stuff is oil colored with steel particles, most of which come from pin and sleeve wear, which causes the elongation of the sleeves in the links. The rate of wear is mostly a result of how clean the chain is.
Cleanliness and Lube
Chain and gear wear depends almost entirely on cleanliness and lubrication. For example, chains and gears operated in clean conditions, such as timing chains on vehicles, last for years, spin around millions of times, and go the equivalent of hundreds of thousands of miles before skipping is an issue. So theoretically, if you kept your chain perfectly clean, it would run for thousands of miles without excessive wear or skipping. But it’s impossible to keep it spotless without removing it, submerging it in solvent, and putting it back on. Almost nobody wants to go to that much effort.
Chain Expiration Date
Chain life expectancy depends on who you talk to, but it typically falls in the range of between 1,000 and 3,000 miles. Anywhere in this range is considered safe on gears. Bike shops recommend replacing your chain at these recommended miles. If you’re inclined to change your chain that often then do it.
Gears Conform to Chains
If you do run your chain longer than it’s expiration date, it means that your gears are conforming to your elongated chain, and it won’t necessarily result in skipping. Worn chains and gears can run smoothly and efficiently together, and the fact that your chain is elongated doesn’t mean that your chain will skip. If your bike isn’t giving you any problems with skipping, you can keep riding it if you want to, without changing your chain. If you get more than three or four thousand miles on it don’t worry about it. Just be aware, that you are wearing down your gears, and instead of just replacing your chain, you may been to replace your bike gears as well.
If you’re running an Ultegra or Dura Ace drivetrain — they can take a real beating for years. If you’ve neglected to change the chain, keep riding it until it skips, and then change your cassette, front rings and chain all at the same time. They all wear out together. Switching to a new chain without replacing the gears is a recipe for skipping when the drivetrain has excessive miles. However some riders report 15,000 miles on a single drivetrain without skipping.