Bike Chain Wear Calculator (Chain Stretch Percentage)
How worn a bicycle chain is, from the measured length of a number of links, with the length at which common wear limits are reached.
Results
What this tool does
A chain does not really stretch: its pins and bushings wear, and the pitch between rivets grows. Hold a ruler against the chain, line up a rivet with the zero mark and read how far past 12 inches (304.8 mm) the 24th rivet falls. Many shops replace a chain at about 0.5 % wear on narrow modern chains and around 0.75 % on older, wider ones, because a chain left to wear further drags the cassette and chainrings out with it, which costs far more. Measure a chain under slight tension, or lift it off the chainring.
Formula
wear % = (measured length − n × 12.7 mm) ÷ (n × 12.7 mm) × 100 (pitch of a bicycle chain = ½ inch = 12.7 mm)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
cn | Number of pitches measured (24 = 12 inches) | — |
cm | Measured length of those pitches | mm |
CW | Chain elongation (wear) | % |
ST | Verdict | — |
PP | Average pitch (new = 12.7 mm) | mm |
EX | Extra length compared with new | mm |
L5 | Length at 0.5 % wear | mm |
L7 | Length at 0.75 % wear | mm |
Worked example
- Number of pitches measured (24 = 12 inches)24
- Measured length of those pitches306 mm
- Chain elongation (wear)0.39 %
- VerdictWithin the normal range
- Average pitch (new = 12.7 mm)12.750 mm
- Extra length compared with new1.2 mm
- Length at 0.5 % wear306.3 mm
- Length at 0.75 % wear307.1 mm
Limitations
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.