Do you have an REI nearby where he can go try on shorts? They generally carry a nice selection of mountain bike shorts (liner and shell) in larger sizes. Also consider buying a good pair of technical riding shorts and just wearing them under regular shorts. I make sure the regular shorts have alittle stretch to them however; much more comfortable that way.
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Private docent led mountain bike rides through Limestone Canyon. Go to
letsgooutside.org and register today! Also available: hikes, equestrian rides and family events as well as trail maintenance and science study.