I have full-size spares on both my rides -- mounted under rear bed/hatch. One of them is mounted with the valve stem down -- so one can easily check/adjust PSI. I picked up a nail in my Sport Trac, so I swapped it's spare on last night. It was mounted underneath -- facing up, so you can't get to the valve stem. It only had 21# of air. When I put the spare back in place, is it OK to mount it with the valve facing down (towards ground)? I never go off road. The chances of it being damaged is slim. It's a pain to have to remove the spare -- just to check the air.