Chain wear. It’s something mentioned all too often in bicycle maintenance guides, but rarely correctly understood. It’s a dirty job, but let’s take an in-depth look into what chain wear is, why it matters and how to prevent it from costing you money in the long run.
For this, I spoke with representatives from Shimano, SRAM, KMC, Park Tool and Abbey Bike Tools to help reveal exactly when you should (or perhaps shouldn’t) replace your chain. Roll on this way as I pin down a few thoughts.
The pieces of a chain
A bicycle chain is made up of lots of individual pieces. These are the pin, outer plates, inner plates, bushing and roller. On most modern chains, the bushing is integrated with the inner plate and holds in the circular roller.
Each chain link is joined onto the next, alternating between outer plate and inner plate. A whole chain link is commonly thought as one segment of outer and inner plate together.
A chain has a 0.5in (12.7mm) spacing between pins. This is the chain ‘pitch’ and is an industry standard on multi-speed bikes. (Note: in this article we're only referring to standard ‘derailleur’ type multi-speed bicycle chains.)
What is chain wear?
Chain wear is commonly referred to as ‘chain stretch’, because the chain’s pitch grows in length as it wears. This is the most important type of chain wear, and the growth comes from the bushings wearing with the chain pins. Overtime, the inner diameter of these bushings increase and the pins groove out.
It’s often stated that a worn chain is when it reaches one percent growth from the original 0.5in (12.7mm) pitch.
Another type of chain is wear is ‘slop’. This isn’t as easy to measure, but this side to side chain wear will lead to slow and inconsistent shifting long before any pin wear is seen.
Why should I care?
Chain wear will lead to poor shifting and lost efficiency. Additionally, a severely worn chain is weaker and there’s nothing fun about a snapped chain under power.
Perhaps most importantly though, chain wear can cost you big bucks if left too long. This is because a new chain at a 0.5in pitch is designed to sit deep into the cog. As the pitch increases, the chain rolls higher up on the tooth and causes rapidly increased cog wear as the point of contact is reduced. Too much wear, and the chain will start skipping over the top of the cog.
“If you put an old worn out chain on a new cassette, you can wear out that cassette in just a few rides," says Nick Murdick, hard goods product line manager at Shimano America. "The chain is very efficient at making the gears match the pitch of the chain. So if you replace a chain before it’s worn out, the gears on the cassette and chainring last much longer.”
On this point, we’ve heard of WorldTour teams getting three seasons of use out of the same chainrings and cassettes, purely from replacing chains before they become worn.
Calvin Jones of Park Tool raises an important point in regards to costs of replacement parts. “It's also a consideration of the cost of the cassette and chain. A budget Shimano cassette is nearly as much as the cheap chain. Say both retail for $20. Why not just replace both (and get more wear)? But consider the nice SRAM XX1 cassette, which is about eight times the cost of a chain. [You should] replace this chain often.”
How do I measure for wear?
Measuring for chain wear is done with a chain checking tool or accurate ruler/tape measure. Which method you should use is the cause of much internet debate.
Using a ruler, a new chain should measure exactly 12 inches across 12 links, from middle of pin to middle of pin. The number most commonly agreed on for a worn chain is one percent elongation between links. In reality though, you want to replace the chain before this point.
So therefore anything past 12, 1/16 inches (0.5 percent) would be the time to replace a chain. And anything past 12, 1/8inches (one percent) has been worn to death and so a new cassette is likely needed.
Holding a ruler perfectly straight while lining it up to measure 1/8in is difficult, and with this, chain checker tools provide a far simpler and quicker 'go or no-go' result. Whichever way you choose to measure a chain, be sure to not include any Masterlink, quicklink or 'Powerlock' which may be installed.
Jones brings up the point that the parameters for chain wear have changed as drivetrains have. “Through the years, the replacement standards have changed," he says. "The chains are narrower now, and people are not weaker. Chains don’t last like they used to. Add to this rear sprockets are narrower and think don’t last like they used to. With six- to seven-speed (chains) a one percent wear was the norm, but that is no longer the case.”
Countering Jones’ comment to some extent, Murdick claims the latest Shimano 11-speed chains are far more durable and resistant to length growth compared with previous generation 10-speed and earlier chains.
What is the best chain checker?
There are strong opinions on what style of chain checkers work, and which ones cause premature wear readings. There are articles dedicated to this (such as this), with the general idea being that most chain checkers are susceptible to false reading by taking into account roller movement by pushing the pieces in opposite directions.
Chain checkers from the likes of Shimano and Pedro's isolate roller wear by measuring pin wear in the same direction and are thought be truly accurate across all brands and speeds (6-7-8, 9, 10 and 11) of chains.
“There's really only one dimension that is universally agreed upon: the pitch, or distance from one pin to the next (.5in)," says Murdick of issues over measuring wear. "The diameter or the roller both inside and out, the diameter of the rivet pin, the size of the hole in the inner chain plate which the pin passes through, and the amount of space between the pin and the plate, and the plate and the roller can vary quite a bit from one model to the next.
With most chain wear indicators, he goes on, you’re measuring the elongation of the chain, plus a reduction in thickness in the rollers, and that’s on top of any dimensional difference that is part of the design of the chain.
“The numbers on many chain wear indicators can [also] muddy the waters a bit because they might be indicating millimetres of elongation, percentage wear (as in a chain that is elongated a certain predetermined amount is 100 percent worn), or percentage stretch (as in a chain is worn when it is one percent longer than it was when it was new)," Murdick adds. "So if a tool says that you should replace a chain at .50, it could be talking about any of those three things."
Daniel Slusser of SRAM backs this viewpoint. “Roller movement can dramatically affect readings," he says. "Some tools that can’t differentiate between pin wear and roller movement can lead to brand-new chains reading as worn. Most chain checkers on the market skew conservatively like this, ensuring that your chain reads as worn before you do damage to your cassette.”
Abbey Bike Tools is one cycling tool company that doesn’t make a chain checker.
“The checkers that I don't like are the ones with some kind of a sliding or pivoting indicator," says Abbey owner Jason Quade. "These are dependent on hand pressure to take a reading and, depending on how much pressure that is, they can be way off. While the checkers that take into account roller play, like the Shimano TL-CN41, are a great idea, I haven't found the results between them and Rohloff (drop in type) style tool to be very different.”
Confusing? Put simply, I’m of the opinion that any chain checker is better than no chain checker. Despite what many say, my experience shows that most checkers do what they need to. Either way, check your chain checker on a new chain and make sure it’s not wildly incorrect and costing you unnecessary chain replacements. And remember that most chain tools are 'drop in' style; in other words they don't need to be forced into the chain.
I compared Shimano’s CN-42 checker against the likes of a Park Tool CC-3.2 and a KMC Digital gauge. They measure similar on the modern 10/11 speed chains I checked, signalling wear at about the 0.75 percent point. For example, measuring a well-worn 11-speed Shimano Ultegra chain allowed the Shimano CN-42 checker to drop in and tell me it was worn. It also allowed the 0.75 percent marking on the Park Tool CC-3.2 and older CC-3 to drop in. And my trusted KMC digital checker showed 0.89mm – just after the point of where KMC strongly recommends replacement.
For me, I like the drop-in gauges that give some indication of where the chain is at for its wear, as opposed to something like the one-sided Shimano which just says yes or no with no indication of how long it has been worn for and just how bad it is. And although expensive, I also like the digital gauges from Feedback Sports and KMC. Yes these gauges are affected by roller diameter variances, but I'd much rather replace a chain that's suspected of wear than replace an entire drivetrain later on.
So how often should I replace my chain?
Unfortunately, riding distance is not an accurate indicator of chain wear, and keeping a check on measurement is the only answer. Both Shimano and SRAM refuse to give a gauge of distance.
When not making tools, Jason Quade is a pro-race mechanic. “It's impossible to estimate chain life in distance," he concurs. "There's just simply too many variables at play. At the 2015 Tour of Alberta there was a particularity nasty day of racing over dirt roads while it was raining. The soil was fairly gritty to boot. That single day of racing wore out nearly an entire field's worth of chains in 162km.”
Drop-in style chain checkers can be bought cheaply. Bearing Quade's comments in mind, it's worth using one every few weeks in your general chain lube/wipe maintenance.
The likes of KMC, SRAM, Park Tool and Abbey Bike Tools all agree that the 0.5 percent marking on most chain checkers is a safe point to replace the chain before cassette wear becomes an issue. You can push it out toward the 0.75 percent, but you risk overcooking the situation depending on the checker.
This sits perfectly in line with my personal preference for replacing modern 10-11 speed chains anywhere from 0.4mm on the KMC digital checker, or 0.5 percent on the Park Tool CC-3.2. For me, the likes of the Shimano CN-42 checker (despite its known accuracy across brands/speeds), Park’s older CC-3 and others don’t provide this earlier indication and will only show wear for what I deem too late in order to guarantee against cassette replacement.
What about that chain ‘slop’ mentioned earlier?
Some riders who don't put a lot of torque into their drive train will wear out the chain rollers before wear becomes apparent on a traditional chain checker. "Think of petite riders, or riders that may be of average size but spin a higher cadence," says Quade. "These riders will wear the roller down (side to side, not OD/ID) and the chain gets sloppy side to side but isn't 'stretched'.”
Murdick backs this. “As chains wear, they develop more lateral flexibility, which comes from friction between the inner and outer plates," he says. "That can affect shifting even before the effects of elongation are felt. In fact, the differences in initial lateral flexibility on a new chain vary greatly between chain manufacturers and that does have an effect on shift quality and durability.”
As for a solution, Quade says it’s not so simple. “These chains can be harder to spot for a home mechanic who isn't putting a new chain on somebody else’s bike on a daily basis," he adds. "This wear can cause some pretty sloppy shifting, which is perhaps the easiest way to spot it. The chain will lag behind shifts, similar to the feeling of dirty cables or a B-tension adjustment that's to far out.”
What if my chain is already worn?
Exactly how much wear your chain has will dictate your available options. On terribly worn drivetrains, the teeth of the cogs will begin to look hooked from the chain wearing high on them. If you’re at this point, replacing just the chain simply isn't an option.
Some riders will choose to just let everything wear out until their bike starts skipping gears, but your risk of a snapped chain increases with this. Others will replace chain and cassette, and hope the chainrings are in a re-usable condition. If you do this, any shifting issues, chain suck (where the chain doesn't disengage from the bottom of the chainring) or chain dropping will signal that the chainrings aren’t happy.
“If you're running a basic stamped steel cassette you could probably go past one percent wear and be fine," says Quade. "[But] if you're using an aluminium weight-weenie cassette it could be toast at a 0.5 measurement – the important thing to do is to test your bike after a chain swap.
"When the cassette is worn to the point it won’t mesh with a new chain, it can create a safety issue. So a [quick] spin after you've swapped the chain is never a bad idea. Never allow a new chain to wear into a worn cassette.”
Chain wear is very much like tyre choice or chamois cream – and everyone has an opinion. It’s easy to obsess over the minor details of when a chain is worn, and what chain checker does what. Heck, even temperate plays a role – a chain left in the sun matched with a cold checker will read wrongly.
In the end, though, whenever you’re in doubt over chain wear, replace it – it’ll save you money in the long run.
“We could nerd out on the importance of measuring the chain by tensioning the chain the same way it’s tensioned when riding, or whether it’s better to take our measurement inside the chain circle or outside," says Murdick. "Can you extend the life of your chain by flipping the circle inside out?
"But again, these details are pushing the conversation too far for all but a rare few," he concludes. "The most import thing for any rider to take away is that in the long run, the cheapest way to take care of your drivetrain is to keep the chain clean and lubricated, and replace it before it wears out.”
Perhaps the bigger question is what brand to choose. But we can leave that one for another time.