Belt separation, the final stage of belt edge crack growth, is discussed to illustrate the influence of tire aging to durability. The resistance to crack propagation of aged rubbers correlates well with extension ratio at break λ_b, which is considered to represent the extent of crosslinking due to oxidative aging. Resistance to crack propagation falls with decreasing λ_b, i. e., with crosslinking during aging. Consequently, aging of tire causes deterioration of resistance to belt separation.
Reduced oxygen permeation through tire wall, by means of nitrogen inflation and use of halogenated butyl rubber for inner liner, leads to better durability. It is also found that lower temperature mixing leads to better aging resistance and tire durability.