13 Inch Tires??

http://www.discounttire.com/dtcs/infoTireMath.dos

This will let you make a comparison between 2 different tire sizes.

Going from a 175/80 to a 155/80 will give you a lot smaller tire.

Slip over to any Big Chief Tire outlet and talk to them.
I always used the one at Lem Turner and Dunn Ave. They always treated me right.