*here comes Rowan*
hate to be "dad" n stuff n be all like "son you need to think of your future"
but ask any racer, ANY real racer... you shouldn't apply hippari (stretch) to tyres that have been running without stretch...
ie get new tyres
the rubber on the tyres will have heated up, cooled down, heated up, cooled down gotten wet gotten dry etc etc in the "normal" shape - applying stretch to that rubber will make them crack.