The energy requirement for bicycle riding depends on the cross-sectional diameter of the tires. With the recommended inflation pressures the net O2 consumption is about 0.19 1/minute greater on 26" x 2-1/8" tires than on 26" x 1-1/4" tires. Other data and calculations take into account air resistance, inflation pressure, and characteristics of tread stock. Large tires, commonly provided on American bicycles and rarely on European bicycles, are undesirable for the person who uses a bicycle to get from one place to another with minimal energy expenditure.