mmMeasure pin centre to pin centre on a tight run of chain.
Pins counted minus one.
Result
Elongation1.73 %
How it is calculated, with your numbers
- Length when new
nominal = pitches × p20 × 15.875 = 317.5 mm - Elongation
wear = (measured − nominal) / nominal × 100(323 − 317.5) / 317.5 × 100 = 1.73 %
Working uses the metric units the formula is written in.
- measured Measured length (mm)
- pitches Number of pitches measured
- p Chain pitch (mm)
- nominal Length when new
- wear Elongation
What it means
Chains do not stretch so much as wear: every pin and bush wears a little, and the chain gets longer. Measure a long, tight section, compare with the new length, and express the difference as a percentage.
Chain makers publish a service limit, often around 1.5 to 2% depending on the chain. Use your chain maker's figure, and replace the sprockets with the chain.
Assumptions and limits
- Measured under tension on the bottom run, not including the master link.
Sources
- ISO 606: Short-pitch transmission precision roller and bush chains (chain pitch per size).