Chain sizes look like secret code — 520, 525, 530, 420, 428 — but the system is simple once decoded, and it answers the eternal question of whether that "520 conversion" the forums recommend is worth it.
Decoding the number
First digit: pitch, the pin-to-pin distance, in eighths of an inch. A 5 means 5/8" pitch — which is why 520, 525, and 530 all fit the same sprocket tooth profile. Remaining digits: internal width between the inner plates. A 520 is narrower and lighter; a 530 is wider, heavier, and (within a quality tier) stronger. Small bikes run 420 and 428 — 4/8" pitch — same logic, smaller scale.
Why width matters
Wider chains put more bearing area on the pins and more plate metal in tension, raising tensile strength and wear life. Manufacturers spec chain size to the bike's power and weight with margin — a liter bike gets a 530, a middleweight a 525, a dirt bike a 520 where every gram of rotating weight counts.
The 520 conversion, honestly
Swapping a 525/530 bike to 520 chain and sprockets saves roughly one to two pounds of rotating, unsprung weight at the rear wheel — genuinely noticeable in how the bike revs and the suspension works, which is why racers do it universally. The honest caveats: you must use a premium 520 chain with a tensile rating suited to the bike (budget 520s on powerful bikes wear fast or worse), and expect somewhat shorter chain life than the wider stock size. For track bikes and spirited street bikes, worth it. For a loaded ADV tourer, the stock width's durability margin is the better trade — chain life on big bikes is covered in lifespan numbers.
Rules for any conversion
Chain and both sprockets must match in size — a 520 chain on 525 sprockets is a derailment waiting to happen. Convert as a full kit, which conveniently is how replacement should happen anyway. And gearing changes often ride along with conversions; plan them together with the gearing guide.
Size doesn't change care
A 520 and a 530 want identical treatment: clean all four faces (the CC360 is built for chains up to and including 520 — 525 and 530 owners need a larger brush), lube the inside run, keep slack in spec. A premium narrow chain maintained will outlive a wide chain neglected — width buys margin, maintenance buys miles.
Quick answers
What do chain numbers like 520 mean?
The first digit is pitch in eighths of an inch (5 = 5/8\") and the remaining digits code the internal width. 520, 525 and 530 chains share the same pitch and differ in width and strength.
Can I put a 520 chain on a bike that came with 525?
Yes, with matching 520 sprockets — it's a common weight-saving conversion. Use a high-quality 520 chain rated for your bike's power.
Which chain size is strongest?
Within the same quality tier, wider is stronger: 530 over 525 over 520. But a premium 520 can out-rate a budget 530 — tensile rating matters more than size alone.