Stiff / hard-to-turn steering

Warning: the steering is a safety-critical system — steering that catches or resists, especially in corners and at low speed, is dangerous. Deal with it quickly, and if you have any doubt, get it checked by a professional. The handlebar resists abnormally, catches at center, or takes unusual effort to turn. The most common cause involves the steering head bearings: when worn, they develop notches (a "tight spot" wears into the center position, where the bike spends most of its time rolling straight); when overtightened (excessive preload), they stiffen the rotation. A dry or oxidized steering head (from lack of grease) causes the same stiffness. More simply, a cable (throttle, clutch, brake), a hose, or a wire routed incorrectly can pull on the handlebar at full lock and restrict it, and a badly underinflated front tire makes the steering heavy, especially at low speed. You tell them apart with tests: with the front wheel lifted, do you feel a tight spot at center (bearings)? Does a cable pull taut at full lock (routing)? Is the front pressure correct? Causes tied to the bearings and steering head are classified expert-only (safety-critical part, steering geometry); cable rerouting and tire pressure are things you can handle yourself. Urgency threshold: steering that catches or binds can catch you off guard in a corner or during a maneuver and cause a fall — don't ignore this symptom. Start with the free checks (pressure, cable routing) before considering work on the steering head, which is a job for a professional.