What's the width of your current saddle? Start out 10 mm wider and if that's not enough go wider and if it's too much go narrower. A demo program is key.
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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"