PARIS  They’re clunky, heavy and ugly, but they have become modish  and they are not this season’s platform shoes.

A year after the introduction of the sturdy gray bicycles known as Vélib’s, they are being used all over Paris. The bikes are cheap to rent because they are subsidized by advertising, and other major cities, including American ones, are exploring similar projects.

About 20,600 Vélib’ bicycles are in service here, with more than 1,450 self-service rental stations. The stations are only some 300 yards apart, and there are four times as many as there are subway stations, even in a city so well served by its metro system.

In the first year, the city says, there have been 27.5 million trips in this city of roughly 2.1 million people, many of them for daily commutes. On average, there are 120,000 trips a day. And on July 27, at the conclusion here of the Tour de France, 365 lucky Vélib’ riders will be chosen to ride along for a while and cross the finish line.