A bent rim on a car can cause a number of problems. Bent wheels on the front end of a car can, over time cause the alignment to come out of adjustment because of excess vibration. Excess vibration can also, in extreme situations, cause lug nuts to loosen and come off while driving. Your local tire shop can fix very minor bends in steel wheels. Alloy wheels will require specialized service techniques and machines. In most circumstances, unless the bent wheel is an extremely expensive custom wheel, it will be more cost effective to replace it, instead of paying to fix it.