I have an old huffy 26 inch mountain bike. I changed the tire a couple days ago and now it has a pronounced wobble (side to side movement, not at the axle). Its like its misaligned somewhere but everything seems tight to me. At certain points the rim is dragging on the brakes. Any ideas?
Most likely situation is the wheel isn't full seated in the frame. With the bike standing upright on the ground loosen the wheel bolts and lean a bit on the bike which will force the wheel all the way into the dropouts. While still leaning on the bike tighten the wheel bolts. Be sure to alternate bolts when tightening. A lot of times people tighten one side first and the torque causes the other side of the axle to slide slightly out of the dropout resulting in a wobble.
Is the axle flush in the frame/fork?
Do you have rim brakes? If the rim is old and the brake surfaces already quite abraded, inflating with high pressure or installing a wider tire could have broken or deformed the rim walls.
Was the the wheel true (i.e. no wobble) before? How much wobble are we talking? 1mm? 5mm?