A backwards tube is one of the main causes of carbon frame aspolosion. If you are riding steel or titanium, then you are probably OK. Probably.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"