Ive got a problem with rear tyres 'degrading' after about 1000miles ? small cracks are appearing across the centre 1/3 of the tyre, had this on 2 tyres now, both pirelli diablo, anyone had similar problems with these?? tyre fitter reckons that the tyres are overheating then cooling too quickly? I could understand if i rode like rossi, but 300 miles on the last tyre has been too & from work at sensible speeds? helpful/ unhelpful comments appreciated