OK, I'm going out on a limb here because I haven't paid much attention to the tires on my truck. Steel belted radials should only be run in one direction. If you get a flat, you should put the spare on and drive as short a distance as possible until you can get it fixed. That way you can use the spare on either side of the truck. It has been about 12 years since I worked as an auto mechanic so things may have changed since then. As I said in the beginning, I haven't paid much attention to my tires. I plan on replacing them ASAP. I'm not even sure if the Xterra has steel belted radials I just thought I'd give a reason to not put the spare in the mix.