When to replace a bike chain: how to measure wear and what distance figures are worth

Which wear limit applies to your chain

As the pins wear, the chain's pitch changes, as TOUR explains, and the distance between rivets grows. A gauge reads that growth as a percentage. These are the limits published on the pages we read:

The sources disagree at 11 and 12 speeds: Park Tool says 0.5%, while SRAM says 0.8% for its own chains. Park Tool points out that every maker has its own specs and that those take priority, so on an Eagle or AXS chain SRAM's figure is the one to use, and it applies only to SRAM parts. SRAM adds that replacing the chain too early can also wear the rest of the drivetrain sooner. Shimano recommends a gauge and regular checks during the season, but the page we read gives no percentage. For Shimano and other brands, look for the figure in their documentation.

What each percentage means in millimetres

Twelve inches is 304.8 mm. On an unworn chain, the 24th rivet from zero lands right on that mark; on a worn one, it lands past it. How far past depends on the percentage:

Park Tool's ruler mark, 1/16 in, is 1.59 mm, and 1.59 ÷ 304.8 = 0.52%. That fits its limit for 11 speeds or more, and it sits below the 2.3 mm of its limit for 10 speeds or fewer. Park Tool calls this a ballpark method, and the sums back that up: 0.75% and 0.8% are 0.15 mm apart (304.8 × 0.05 ÷ 100), less than one division on a millimetre ruler.

How to measure chain wear, step by step

Before you measure, Park Tool asks you to check that the shifting is adjusted and the chain is clean and lubed. As possible signs of a worn chain it lists slipping under load and the chain clinging to a chainring as you shift. If you notice either, measure. With a ruler:

1. Line up one rivet with the zero on the ruler.
2. Count 24 more rivets from there.
3. See where the last one lands: it should sit on the 12-inch mark.
4. If it is more than 1/16 in (1.59 mm) past the mark, Park Tool says it is time to replace the chain.
5. If it comes close, confirm with a gauge. This last step is our own judgement.

A gauge gives you a direct reading. Park Tool describes three kinds:

• Three-point: works on 5- to 12-speed chains, including 12-speed SRAM AXS, and marks 0.5%, 0.75% and 1%. Keep tension on the short section of chain, a step Park Tool calls crucial.
• Go/no-go: hooks onto a roller between inner plates. If the 0.5 side will not go in, the chain is under 0.5%; if it does, the chain is at least 0.5% worn. The other side checks 0.75%.
• With a readout: one stud goes between outer plates and the other between inner plates. Press the lever lightly up to its stop, without forcing it, and read the percentage in the window.

Shimano asks for regular checks during the season without setting an interval. Our own rule of thumb, with no source behind it: measure once a month if you ride every week, and again after a spell of rain or mud.

Why «how many km» has no universal answer

Park Tool gives no distance, and neither do the SRAM and Shimano pages we read. The distance figures that do exist come from tests or design decisions, and each has limits:

The sums: 12.7% of 0.5% is 0.06% wear, and 110.2% of 0.5% is 0.55%, already past that limit. Over the same distance, that is nearly nine times the wear (110.2 ÷ 12.7 = 8.7).

On the road, TOUR's figure describes a very favourable case. For MTB we found no distance from any maker. The closest thing is Zero Friction Cycling's 1,000 km dust block, meant to stand in for dry gravel and MTB: the 5 lubes with the least wear stayed at 2.6% of the allowance, and the 5 drip lubes with the most reached 71.3%. TOUR adds that small cogs and small chainrings load the chain harder, which is why 100 km is not always 100 km.

A made-up example: 150 km a week

This example is made up. Someone rides 150 km a week and goes by the 4,000 km Pedalytics reference, which warns between 80% and 90% of that figure. 4,000 ÷ 150 = 26.7 weeks, a little over six months.

• Warning at 80%: 4,000 × 0.8 = 3,200 km; 3,200 ÷ 150 = 21.3 weeks.
• Warning at 90%: 4,000 × 0.9 = 3,600 km; 3,600 ÷ 150 = 24 weeks.
• Reference reached: 4,000 km, at 26.7 weeks.

Measuring once a month, about 600 km between readings (150 × 4), that rider gets five readings before the first warning (3,200 ÷ 600 = 5.3). The reading is what decides. If the gauge shows the chain's limit at 2,000 km, it is time to replace it with 2,000 km still to go on the reference. If it shows half the limit at 4,000 km, the rider can keep going.

When it is time to replace it

Riding a chain past its limit wears cogs and chainrings sooner, and Park Tool reminds you that a new cassette costs far more than a new chain. TOUR adds that late replacement or poor upkeep multiplies the cost.

• Fit the new chain on your cassette and pedal hard, as a practical check: if it skips under load, see when to replace the cassette.
• Before you cut it, work out the number of links with the calculator.
• On Eagle, SRAM says that replacing the chain before 0.8% and cleaning it routinely does the most to extend cassette and chainring life. Here is how to clean and lube it.
• Log the distance at the swap in your maintenance schedule, so you can compare it with the next chain.

In Pedalytics

Pedalytics is not out yet: it is listed as «Coming soon». Each ride stores a snapshot of the setup and adds wear to the parts that were on the bike. The chain has a 4,000 km reference: the app warns between 80% and 90% and treats it as due on reaching that figure. A part can start as new, used with its distance, or unknown; if it is unknown, the percentage is a minimum.