Split Rim on 1958 Ford Mainline Ute

[rotorwrench]

I can't tell for sure from the photograph but there appears to be a small pucker in the edge. It likely cracked whenever that happened and the crack grew from stress & fatigue. Any tire puts pressure there in turns but radial tires add a bit more leverage to the mix and therefore more pressure in a hard turn. Wheel rims can corrode in that area too from moisture seeping in so that doesn't help.