Personal experience with steel frame failures:
1960 Capo Modell Campagnolo (db 531) -- downtube cracked behind head tube, just past butting taper, but frame had been bent back and straightened and was thus being ridden on borrowed time
1971 Nishiki Competition (db CrMo) -- seat tube lug broke off of bottom bracket shell at 40K mi / 20 year mark.
1973 Peugeot UO-8 (plain gauge carbon steel) -- chainstay cracked between the tire and chainring clearance dimples
Personal experience with steel rear axle failures (always drive side, adjacent to bearing cone):
1 solid French axle, 120mm OLD
1 hollow (QR) French axle, 120mm OLD
1 hollow (QR) Campag. axle, 126mm OLD, 25 years old
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069