I have a 2001 Yukon that has the original Firestone spare tire. It looks in good conditikn with no visible cracks, dry rot, or other degradations, and it holds its pressure, but it IS 20 years old. It has probably ever been on the road once. Should I just replace it with a new one, or could this tire still be a reliable spare? Some places I go, it might have to survive 50 miles of gravel roads and 150 miles of highway before being removed again.