tyres
Main landing gear tyres on the B733 last about 3 months, depending on average weights. Nose gear tyres dont last that long as they are very suseptable to side loadings and flat spots causing vibrations. They are retreaded in Victoria, and have a life of about 5 years. Most airlines now only lease the tyres from the manufacturer, and pay what they use.
Sunfish is correct that heat and overloading is the big killer of tyres. Taxi at high speed at high weight is the worst condition for tyres causing high side wall tempratures that can destroy a tyre.