Are you leaving the bike with very flat tyres for a long period of time and then jacking the pressure up high? Sometimes I have seen similar when old tyres have been left empty with the weight of the bike on the folded sidewall, the rubber perishes and then splits when pumped up.
Are you leaving the bike with very flat tyres for a long period of time and then jacking the pressure up high? Sometimes I have seen similar when old tyres have been left empty with the weight of the bike on the folded sidewall, the rubber perishes and then splits when pumped up.