The bottom drawings show the anthropometric relationship between shod foot length and tread depth. Ninety-five percent of users with heavy winter boots have a shod foot leangth of about 9 in, or 22.9 cm, or less. The 9.5 in, or 24.1 cm, tread presently in common use allows comfortable tread contact for only 5 percent of the users, while the foot of the larger user overhangs the tread by more than 5 in, or 12.7 cm, certainly a cause for concern, especially for old and physically disabled people.