A sturdy mountain bike, a rugged tent, and an extensive knowledge of bicycle repair: That's what you'll have to bring on a two-wheeling trip along the Carretera Austral, since services are few and far between. Recently completed to the southern outpost of Villa O'Higgins, this is a discontinuous penetration road from Puerto Montt that passes through some of the most spectacular wild terrain in the country, if not on the entire South American continent. Increasing numbers of cyclists, some of them thru-riders from Alaska to Tierra del Fuego, are braving the changeable weather on this 680-mile road, which, except for a few paved sections around the regional capital of Coyhaique, is mostly gravel.