Pretty sure they are rubber. I smack them with a hammer, and it bounces back, and they still work perfectly. Maybe its because I rotate them when I should and check the pressure in them?
I could rotate tyres all I want, but i'll never get more than 12K combined out of any tyres that are on the front of my ST My pressures are also spot on
Guess it's down to a complete lack of power going through your tyres