What are bearings on a mountain bike?

What is a bearing? A bearing is used to reduce friction between two surfaces. You can find bearings in the front or rear hub in your wheels, inside the bottom bracket where the axle is connected to the cranks and in the frame where your headset sits. All these are applicable to either mountain bikes or road bikes.

What are crank bearings on a bike?

The crank bearings are part of the bottom bracket assembly that slots into the round bottom bracket shell on the bicycle frame. This part will contain the spindle that is the axle of the crankset; this part allows the bearings to move smoothly.

Are all bicycle crank bearings the same size?

While modern road cranks are compatible with many different types of bottom bracket shells, some combinations are better than others. Shimano (left) and GXP (right) crank axles share the same diameter — 24mm — however the end of each axle is quite distinct.

How do I know if my crank bearings are bad on my bike?

The sound should remain smooth, quiet, and even but if there are bumps, gaps, or any loud noises, this is a sign that the bearing is dry or worn out. This will call for either a bike bearing overhaul or a complete replacement.

What does a bad crankshaft bearing sound like?

Crankshaft bearing noise is also caused by low oil pressure which damages the bearing surfaces and could eventually damage the crankshaft itself. This type of noise is usually described as a rumbling or thumping sound deep in the engine when accelerating.

What causes bike bearings to go bad?

Or in the case of sealed-bearing hubs, either the bearing(s) is worn out, or the grease inside the sealed cartridge bearings in these hubs has been all used up over time. When this happens, since the grease takes up space inside the bearing, it can result in play in the bearings.

When should I replace my bottom bracket bearings?

There’s really no periodic time period for BB replacement. You run em till they die. If the bearings are smooth without any perceptable play, then they are fine. When things eventually get contaminated (if they ever do), then you’ll notice roughness, crunchiness or significant play in the bearings.

What does a bad bottom bracket sound like?

Most surprisingly, what often sounds like a bottom bracket creak is usually something else. Most of the time, the true cause is a loose chainring bolt. Tighten ’em up and that’ll quiet most creaks. Sometimes even when a bike is new from the factory, the BB isn’t tight and it creaks.