The length of a motorcycle chain is given in links (pitches), not in millimetres. It depends on the chain pitch, the tooth counts of the front and rear sprockets and the centre distance from the gearbox output shaft to the rear axle. The same formula works for every roller chain; on a motorcycle the chain adjusters then take up the difference between the calculated and the real centre distance.
TorqueMath · checked against the standards listed below and the calculator’s test cases · Updated
The link formula
X number of links (pitches), C centre distance, p chain pitch (same unit as C), z₁, z₂ tooth counts of the front and rear sprocket.
Round the calculated X down and up to the neighbouring even numbers. A chain with an odd number of links needs an offset (cranked) link, which is weaker and is generally not used on motorcycles. For both even counts work out the centre distance they need and check which one leaves enough adjustment within the permitted adjuster range. Do not simply choose the longer chain.
The result is a calculated starting length, to be checked on the motorcycle: fit the chain with the axle in the adjusters and set the slack the way the motorcycle maker specifies. On many bikes the chain is tightest at a particular swingarm position, so the slack must be set with that in mind.
Chain sizes: 420, 428, 520, 525, 530
For the three-digit codes listed here, the first digit gives the pitch in eighths of an inch. The other digits code the chain version, mainly the width series; take the actual inner width from the dimension table.
| Size | Pitch | Inner width | Typical use |
|---|---|---|---|
| 420 | 1/2 in = 12.70 mm | 6.35 mm | mopeds, small 50–125 cc bikes |
| 428 | 1/2 in = 12.70 mm | 7.94 mm | 125–250 cc |
| 520 | 5/8 in = 15.875 mm | 6.35 mm | enduro, motocross, many sport bikes |
| 525 | 5/8 in = 15.875 mm | 7.94 mm | middle-weight and large road bikes |
| 530 | 5/8 in = 15.875 mm | 9.53 mm | large and older heavy bikes |
Typical uses are only a guide. Always fit the size and type (plain, O-ring, X-ring) that the motorcycle and sprocket maker specify.
What a sprocket change does
The (z₁ + z₂)/2 term means that each extra tooth, front or rear, adds about half a link. Two more teeth on the rear sprocket therefore need about one more link. Because the count must stay even, a small change often fits the old chain and only moves the rear axle.
- Rear axle position: two links more or fewer move the axle by about one pitch, about 16 mm on a 520/525/530 chain and 12.7 mm on a 420/428 chain.
- Gearing: the ratio is z₂ / z₁. More teeth on the rear or fewer on the front give more pulling power and less road speed at a given engine speed.
- Wrap and wear: very small front sprockets (fewer than about 15 teeth) wear the chain faster and run less smoothly.
Measuring the centre distance and the old chain
- As a reference, measure with the rear wheel in the middle of the adjuster range, so a new chain can be tensioned and re-adjusted later. The actual fitting follows the motorcycle maker's procedure.
- Measure C from the centre of the gearbox output shaft (front sprocket) to the centre of the rear axle.
- Or count the old chain: in the usual motorcycle chain length, one pitch corresponds to one pin or roller position. On a closed chain count all pins once round, including the master link. Do not count inner or outer plate pairs.
- Calculate X, round up to an even number, and check the resulting centre distance against the adjuster range.
Replace chain and both sprockets together when the chain is worn, and follow the chain maker's wear limit and master-link recommendation. Many makers require a riveted master link on larger bikes.
Choose the master link for the exact chain model, not only the size: links from different chain models of the same size may not fit.
Worked example: 520 chain, 15 / 45 sprockets, 600 mm centre distance
- Pitch p = 15.875 mm (520), z₁ = 15, z₂ = 45, measured C = 600 mm with the axle in the middle of the adjusters.
- X = 2 × 600 / 15.875 + (15 + 45)/2 + ((45 − 15)/(2π))² × 15.875 / 600 = 75.59 + 30 + 0.60 = 106.19 links.
- Neighbouring even counts: 106 and 108 links. The calculator gives a centre distance of 598.4 mm for 106 links (1.6 mm forward of the measured 600 mm) and 614.4 mm for 108 links (14.4 mm further back).
- At 600 mm the calculated length is closer to 106 links. Which length is actually right depends on the permitted adjuster range, the intended chain tension and the maker's data, so check both before choosing.
- With a 47-tooth rear sprocket: X = 107.28; the neighbouring even counts are 106 (589.8 mm) and 108 (605.8 mm). The ratio goes from 3.000 to 3.133, so road speed at a given engine speed drops by about 4 %.
For the given values X ≈ 106.19 pitches. Standard lengths of 106 and 108 links come into question first, corresponding to centre distances of about 598.4 mm and 614.4 mm. Without the actual adjuster range neither length can be chosen definitively: check both on the bike.
Common mistakes
- Counting plates or pairs instead of pins. The link number counts pitches: one pin = one link.
- Always rounding up, or rounding to an odd number and fitting an offset link. Compare both neighbouring even counts.
- Measuring the centre distance with the axle fully forward or fully back, leaving no adjustment for tension or wear.
- Mixing 520, 525 and 530 parts: the pitch is the same, but the widths differ and the sprocket must match the chain.
- Fitting a new chain on worn sprockets. A worn sprocket wears the new chain quickly.
- The calculated link count is a starting value. Check it on the bike and set the slack as the motorcycle maker specifies.
Sources and standards
- ISO 10190:2008 – Motorcycle chains: characteristics and test methods. ISO 606 and ANSI B29.1 cover general roller chains and do not replace the motorcycle-specific requirements; choose chain and master link to the motorcycle and chain maker's specifications.
- Dimensions of 420–530 chains: chain maker's dimension tables (for example D.I.D).
- Link formula: standard roller-chain geometry, as in the chain makers' handbooks (e.g. Renold, Tsubaki, Iwis) and Roloff/Matek Maschinenelemente, implemented in our chain calculator, how it was checked.