How do I know if my bike chain needs replacing?

Measure it with a chain-checker tool. When it reads 0.75% on a modern 11- or 12-speed drivetrain, the chain is worn out and should be replaced. A ruler works in a pinch: 24 links should measure exactly 12 inches pin-to-pin when new — if it's stretched past 12 1/16 inches, replace it.

How many miles does a bike chain last?

Most chains last 2,000 to 3,000 miles, but it ranges from under 1,000 miles for an e-bike or a rider in wet, gritty conditions to 4,000+ for a clean, well-lubed road chain in dry weather. Mileage is a better guide than time, which is exactly what Pedal Wrencher tracks for you.

What happens if I don't replace a worn chain?

A worn chain wears its cassette and chainrings into a matching worn shape. Fit a fresh chain onto that worn cassette and it skips under load. Replace the chain on time and you keep reusing the expensive parts for far longer.

Can I just replace the chain and not the cassette?

Yes — if you catch it at 0.75%. The whole point of replacing on time is that a fresh chain still meshes with a lightly-worn cassette. If you've ridden well past 1% wear, plan on replacing the cassette (and sometimes chainrings) at the same time.

When to Replace a Bike Chain (the 0.75% Rule and Mileage Guide)

A bike chain is a wear item — a chain of tiny bearings that lengthens as it grinds against itself under load. The trouble is that a worn chain doesn't just wear itself out; it quietly drags your cassette and chainrings down with it. Replace it on time and it's a cheap, quick job. Miss the window and one $30 part turns into a $150 drivetrain.

The 0.75% rule

Chain wear is measured as elongation — how much longer the chain has stretched compared to new. The number that matters:

Chain wear	What it means	What to do
Under 0.5%	Healthy	Keep riding, keep it clean and lubed
0.5% – 0.75%	Approaching the limit	Order a replacement chain
0.75%	Worn out (11/12-speed)	Replace the chain now
1.0%+	Overdue	Replace chain and likely the cassette

For modern 11- and 12-speed drivetrains, 0.75% is the replacement point. Those narrow chains and cassettes are less tolerant of wear, so some mechanics replace 11- and 12-speed chains even earlier, around 0.5%. Older 8- to 10-speed setups are more forgiving and can run to 1%.

Replace at 0.75% and a fresh chain keeps working with your existing cassette. Wait until 1% and the cassette teeth have worn to match the stretched chain — so a new chain skips, and you're buying a cassette too.

How many miles is that?

Wear is what actually matters, but riders think in miles, so here's the rough translation:

Riding style / conditions	Typical chain life
Road, dry, clean and lubed	2,500 – 4,000 miles
Mixed / all-weather road	1,500 – 2,500 miles
Gravel or mountain, dusty or muddy	750 – 1,500 miles
E-bike (mid-drive motor)	1,000 – 1,500 miles

These are ballparks. The single biggest variable is grit: a chain run dry and dirty can wear out three times faster than the same chain kept clean and lubed. This is why a mileage number beats a calendar reminder — 2,000 miles of dry summer road is nothing like 2,000 miles of winter grit.

Why mileage beats a calendar

"Change your chain every year" is bad advice because it ignores how much — and where — you actually ride. A weekend rider and a bike commuter putting in 150 miles a week will hit 0.75% months apart. The honest answer is: track the miles and check wear at the interval those miles suggest.

That's the whole idea behind Pedal Wrencher. It connects to Strava, counts the real miles on each bike, and emails you when your chain is due — so "check the chain" happens at 2,000 miles, not when you finally remember. Replaced it early? Add #pwchain to your next ride and it resets the gauge.