Drivetrain wear: What needs replacing and when?

By Christian Jensen - 08.03.2026

The drivetrain is one of the most important systems on a bicycle. It’s the collection of components that transfers power from your legs to the rear wheel — and because it’s constantly in motion, it wears out over time. High‑end components like Shimano XTR or SRAM XX often wear even faster due to their lightweight construction. Depending on your setup, replacing a full drivetrain can be expensive, which is why regular inspection is essential.

During spring maintenance, many riders discover parts that should be replaced. This guide will help you identify worn components and decide what needs attention. For Shimano users, I often recommend SLX as a cost‑effective and durable option. However, many online shops now price SLX close to XT, so I usually end up choosing XT. In addition to the drivetrain itself, it’s important that the rear hub and bottom bracket are in good condition.

Cassette

The cassette is the cluster of sprockets mounted on the rear wheel. Depending on the age and price of your bike, it may have anywhere from 5 to 11 gears, though modern mountain bikes typically use 9, 10, 11, or 12‑speed systems.

If you ride regularly, especially in races, a cassette can wear out within two years. Ideally, it should be replaced annually. Shimano SLX and XT cassettes usually last around two years, while XTR may wear out in a single season.

Signs of a worn cassette

• Teeth are rounded off on the trailing edge
• The chain slips under load
• Missing teeth (a clear sign it’s overdue for replacement)

Tools needed

• Chain whip
• Lockring tool
• Ratchet or adjustable wrench

Chainrings

Mountain bikes typically have two or three chainrings mounted on a spider, which is attached to the crank arm and bottom bracket. Although manufacturers combine these parts in different ways, the chainrings themselves are always replaceable.

Chainrings are larger than cassette sprockets and therefore wear more slowly. A common rule is to replace the front chainrings every second time you replace the cassette.

Signs of worn chainrings

• Teeth are sharpened or shaped like shark fins
• Shift ramps or pickup pins are worn or broken
• The chain skips when shifting to a larger ring

You can replace individual chainrings as needed.

Tools needed

• Hex/Allen keys
• Crank removal tools (varies by brand)
  • Modern Shimano cranks: internal hex
  • SRAM GXP: larger internal hex on the left crank arm

Jockey wheels (Pulley wheels)

The two small wheels on the rear derailleur are called jockey wheels or pulley wheels, typically with 11 teeth. These rotate far more times than your cassette, often 2–3 times as many, and are exposed to mud, grit, and impacts.

They don’t transfer power, so they don’t wear as aggressively as the cassette, but they do accumulate dirt and can develop play.

Replacement interval

Every 2–3 years, unless damaged.

Tools needed

• Hex/Allen keys

Shifters

Shifters themselves wear very slowly. The derailleur pulleys handle most of the movement at the rear, and the chain handles the load at the front. Shifters may only need replacement every four years, unless damaged in a crash.

Occasional cleaning and lubrication of internal springs and bearings can extend their life significantly.

Tools needed

• Screwdriver
• Hex/Allen keys

Chain

The chain is the fastest‑wearing part of the drivetrain. After thousands of rotations, the pins and rollers wear down, causing the chain to stretch and develop sideways play. This leads to poor shifting and, in the worst case, chain skipping under load.

A chain should typically be replaced twice during the lifespan of a cassette. Installing a new chain on a heavily worn cassette can cause skipping because the two components wear together.

How to check chain wear

Use a ruler with inch markings:

• Measure 12 full links (one inner + one outer link = one full link)
• If the length is 12″ to 12 1/16″, the chain is OK
• Between 12 1/16″ and 12 1/8″, replace the chain
• Beyond 12 1/8″, both chain and cassette are worn and should be replaced

Tools needed

• Chain tool (chain breaker)

Drivetrain Inspection Checklist