How much will adding 16 lb to my car affect ET/mph(rotating weight)

Locomotion thanks for all of that,
adding weight is something i'm considering. What is the least expensive way to add weight.(safely) with the price of lead. A lead bumper is out of the question.:D
Each tire/wheel combo weights 8 lp so it 16 total. the 32 was double weight to get translate it to car weight to us the 100 per a tenth .100 rule
Fill the spare tire with water.