Heres a head scratcher for Mr Bornman or......

[HomerSimpson]

Just a quick note on the compounds used for road tyres (someone said something about these being fancy polymer compounds):  they are all still by and large butyl rubber (some are rubber blends, but essentially all are butyl).  Butyl has a low gas permeability, and more importantly does not oxidize very easily (unlike natural rubber or butadiene rubber for example).  Chances of your tyres degrading before they are worn through are pretty slim.  Having said that, I have one old tyre in my garage which spent about 12 years on an old Peugeot Rapport (from 1988 to 2000) which is pretty much a collection of rubber crumbs held together by dirt and brittle fibres.

[GoLefty!!]

Correct Homer, the casings simply work harden.

SOme tyres with higher silica content due tend to crack up faster than thopse tyres using carbon black is filler in the rubber.