Standard steel for the spare.Check your OEM valve stems for the slow leak.It is a good idea to have all the OEM stems replaced with better grade steel stems..
Rich& Helen N.Ridgeville,Ohio.
F-350SD, Lariat, V-10,4:30 Diff, tow command Long bed, Crew Cab Dually, 06 3400RL
Mor-Ryde Pin Box