Spin Each Wheel for True and Smooth Bearings

Lift each end of the bike and spin the wheel, watching the rim pass a brake pad or the frame. A slight side-to-side wobble can be trued by a shop for little money; a big buckle or a flat spot points to a bent rim and possibly a new wheel. Feel and listen while it spins, too. The hub should turn quietly and freely, with no grinding or rough patches. Squeeze neighboring pairs of spokes as you go around: one that feels slack, or one that is missing altogether, explains a wheel that won't stay straight.