There is an advantage to Philadelphia's trailing all the U.S. cities that have already launched bicycle-sharing programs as an exciting new form of public transportation. Now the Nutter administration can learn from their experiences.

As Mayor Nutter's aides begin their quest to put a fleet of rental bicycles in place, the public is asking a number of crucial questions: How many bikes? What areas of the city should host docking stations, where cyclists pick up and park their two-wheelers? What will be the sources of funding to cover the initial costs to get the system up and running?

The mayor's plan, announced Friday, relies on $3 million in city funding, with as much as twice that amount coming from private sources and state and federal grants to buy bikes, set up stations, and establish the program.

The city would field a modest fleet of just 650 bicycles in 2014 - bikes that would be free to ride for the first half-hour and cost a metered rate after that under a system where riders pay a periodic membership fee. The following year, the system would grow to 1,200 bikes with 120 docking stations across Center City, north to Temple University and west to the University of Pennsylvania.

That's an impressive plan, putting rental bicycles within reach of the thousands of Philadelphians living and working downtown. Joining the ranks of metro areas where bike-sharing already has taken hold can only enhance the city's attractiveness, especially to younger residents.

In one major city after another, though, officials are finding that it makes sense to think big. And by some experts' reckoning, Philadelphia officials run the risk of thinking too small.

A bike-share system ideally should extend beyond Center City, both as a means to boost ridership and to defuse any downtown vs. neighborhood issues to which City Council no doubt will be sensitive. Some bike-share advocates envision a footprint stretching as far north as Temple Hospital and south to the Navy Yard - tailor-made for commuter cycling to the subway at Pattison Avenue.

Such a plan could require doubling the planned fleet, along with the number of docking stations. But a more expansive system may be just what the city needs - a system that transit-dependent suburban communities (think Jenkintown) would seek to partner with at some point.

While the city's bike-share system is still in the planning stages, it's worth exploring whether a larger system makes sense. At least, it would be prudent to build the capacity to expand quickly if it becomes clear that bike-sharing, as expected, becomes the next cool Philly thing.