Why do larger people go downhill faster?

Surface as well as cross sectional area of an object (a human body) increases more slowly than its weight (volume). Therefore, wind drag, that is largely dependent on surface, is proportionally smaller for a heavier and larger object than a smaller one of similar shape and composition. A good example is dust at a rock quarry that remains suspended in the air for a long time while the larger pieces such as sand, gravel, and rock fall increasingly faster to the ground. They are all the same material and have similar irregular shapes but have different weight to surface area ratios, and therefore, different wind resistance to weight ratios. This applies equally to bicyclists coasting down hills if other factors such as clothing and position on the bicycle are similar.