Vibration / pulsing in the lever when braking

Warning: braking and handling are safety matters — when in doubt, get it checked. When you brake, the lever or pedal pulses, "beats" at a regular rhythm, and you feel vibration coming up through the fork or the bars. This rhythmic sensation, which speeds up as you go faster and slows as you slow down, is characteristic: braking force varies with every wheel rotation because something in the disc/pad/wheel assembly isn't uniform. The most frequent cause is a warped brake disc (deformed, no longer perfectly flat); next come an excessively worn disc (below minimum thickness, which overheats and deforms), unevenly worn pads (a dragging caliper piston wearing one pad at an angle), and, not to be overlooked for safety, a loose wheel or wheel bearing play. The distinction comes from tests: do the pulses follow the wheel's rhythm (disc)? Are the pads worn evenly or at an angle? Is there play at the wheel (bearing)? Urgency threshold: light pulsing from a slightly warped disc still allows careful riding while getting it fixed promptly, but a badly warped/worn disc, or especially play at the wheel (bearing, a loosely tightened axle), are safety defects to address without delay. At the slightest doubt about wheel integrity or braking effectiveness, don't ride and have it checked by a professional. The rhythm of the pulses (do they follow the wheel?), pad wear (even or angled?), and any play at the wheel are the three observations that pinpoint the cause.