Not long ago I ran over my son's bike when he left it blocking the garage door. (Its not like I *ever* told him not to leave his bike in that exact spot.)
Old bike wasn't salvageable, and he was due for a new one anyway. He chipped in $15 of savings and $100 later we picked up a 21" Mongoose from the big red box store. The bike came --poorly assembled-- with a front disk brake.
We spent two hours trying to get the caliper, caliper brackets/carrier and pads aligned.
Basically, since only one pad moves, there seems to be no way to align the brake caliper with the disk so that when the brakes are applied the disk *does not* deform. Is this how these setups are supposed to work?