Any part that is generally considered easily replaceable or a 'wear item' - tires, tubes, bearings, brake pads, spokes... is usually not covered by warranty unless it is a very early or unusual failure. A bearing wearing out after a year of use is unlikely to be covered, but a bearing that breaks in half after two weeks of riding probably will be. As OP found, companies will often give you the benefit of the doubt, especially for smaller or lower cost parts.