MTB Bearings

How to choose your MTB bearings

A bearing is not chosen by bike brand, but by its dimensions. These are stamped on the side of the worn bearing, or can be measured with a vernier calliper. Once you know the part number, any reputable manufacturer will do.

Reading the part number

• The part number encodes three dimensions in millimetres : inside diameter, outside diameter, width.
• 6902 corresponds to 15 x 28 x 7 mm, 6802 to 15 x 24 x 5 mm, 6903 to 17 x 30 x 7 mm.
• The suffix 2RS means two rubber contact seals: this is exactly what you need on an MTB.
• The prefix MR indicates a bike-specific dimension outside standard industrial sizes — for example MR-2437 for 24 x 37 x 7 mm.

Which quality grade to choose?

• ABEC 3 : the standard choice, more than adequate for an MTB hub and offering the best lifespan-to-price ratio.
• ABEC 5 : tighter tolerances, smoother unladen rotation, advantageous for racing.
• Ceramic : superior efficiency and good performance in wet conditions, but at a vastly higher cost.
• On an MTB, sealing matters more than precision : water and mud are what ruin bearings, not rotational speed.

Where they are found on an MTB

• Front and rear hubs, including inside the freehub body.
• Bottom bracket.
• Frame pivots on a full-suspension bike.
• Headset, and jockey wheels on models with cartridge bearings.

Replacement

Always replace bearings on the same hub in pairs: the second one will soon fail as well. Use a bearing puller and a press rather than a drift and a hammer, and never strike the inner race, as this marks the tracks of the new bearing. On Shimano loose-ball hubs, replacement involves fitting new ball bearings and fresh grease.

To find out more: How to maintain your MTB hubs

See also: MTB hubs · MTB bottom brackets · MTB headsets