Originally Posted by JerrySTL

Over. The tire circumference is actually smaller so you are getting more revolutions for a set distance. These revolutions are being computed for a larger tire.

BTW: The best way to set the computer is with a roll-out measurement. Inflate the tires to the proper pressure; place the valve stem at the 6 0'clock position; mark the sidewalk with a piece of chalk or something; sit on the seat; and roll one revolution to where the valve stem in back at the 6 o'clock position; then mark it. Next measure the distance between the two marks with a tape measure. Most have CM on them. Enter that into the bike computer. If the computer takes MM just multiply the CMs by 10. Much more accurate.