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will be run at fairly low pressure 80pis
80psi is not "fairly low"
Cracked rubber is usually a sign of age embrittlement, and where the rubber leads, the nylon carcase threads usually follow. That said, I've seen much worse being ridden, and the fact that it's separated at the join probably says more about how badly the two-shot moulding was done in the first place than the level of deterioration since.
gbj_tester-
Thanks, that seems sensible. In terms of the strength of the tyre (resisting the pressure from the inner tube) my hunch was that the carcass does the heavy lifting and it's too much of a coincidence that the crack is at the colour boundary. Presumably the risk you're referring to is of the carcass also being old and brittle rather than a cascade failure of the rubber then the carcass.
ffm
What's the general opinion on tyre sidewall cracks? This appears to have parted between the tan and black sections. It will be run at fairly low pressure 80 psi but might see some loaded and/or towpath use.