Q: Can 16 inch tires / rims be used on a car that came stock with 17 inch tires / rims?

Hi there - the answer is "possibly". There are 4 technical questions which must be affirmatively answered first to go forward with this swap. First - do the wheels you acquired have the same bolt pattern as your stock wheels (i.e. same # of bolts, and same bolt hole circle diameter - 100mm, 5" or whatever)? Second - do the newly acquired 16" wheels fit over your brake calipers and discs with at least 1/4" clearance everywhere? Most likely they do, but some cars have very large diameter discs these days, which require large diameter wheels. Third - do the new wheels (with a representative tire size you intend to use) bolt squarely to the hubs without rubbing against any suspension bits (i.e. strut tower, tie rod end, sway bar links, etc.)? Fourth - do the new wheels have the same size (or larger) center hole, which matches the diameter of the hub, so that the wheel center carries the load of the vehicle, and not the wheel lugs? If the wheel hole is larger than the hub, you can likely purchase concentric rings which fit between the hub and wheel, centers the wheel, and enables direct weight load transfer to the wheel. If all of these questions have the correct answer, YES, you can safely use your newly acquired wheels, even though they are 1" smaller in diameter. Happy motoring!