Thanks, Denver. I, too, would be interested to hear what Jobst has to say about this.
I concur with the others that this is NOT a rim sidewall erosion issue.
This story reminds me of one of our early 1970s Bikecology customers. This teenager, who weighed about 250lbs / 115kg, promptly pretzled the OEM Rigida steel rim on his new Peugeot UO-8. To prevent recurrence, I rebuilt the rear wheel with 14 ga. spokes and a steel Schwinn rim.
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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