The garages are filling, the crews and drivers arriving and final preparations underway for the second most important day of the year for the 2012 Le Mans 24 Hours race entrants, the “Official Test Day” this Sunday, June 3.

The Le Mans circuit is a stunning 8.462 miles in length, but includes a number of public roads that limit the availability of the full circuit to the single Official Test Day and a pair of mid-race week practice and qualifying evening sessions in advance of the June 16-17 race.

Each entrant has a very long checklist of things to accomplish in the limited track time on Sunday. New drivers must become oriented to the circuit, new cars shaken down, set-ups tested and compared, gearing confirmed, brakes and tires evaluated, fuel mileage determined and team procedures locked down.

Like the start of baseball’s spring training, hope springs eternal for each team. Is this their year?

For the defending champion Audi Sport and Corvette Racing teams, Test Day pushes the trials and successes of 2011 deep into the background. A new race will be run and last year is ancient history.

Test Day is especially important for the newest cars, the Audi R18 e-tron Quattro and the Toyota TS 030 Hybrid. In addition to all the usual areas of focus, the hybrids must recognize and assess the recently announced braking zones for energy recovery.

Drawing particular attention will be the experimental Nissan DeltaWing, the special 56th entry for this year’s race.

Sunday will leave some teams enthused, others frustrated and more than a few scrambling. There is just a small window between the test day and the start of Scrutineering seven days later to assess the results, make major changes, re-evaluate strategy and fix any problems.

The Le Mans 24 Hour race countdown begins with a calendar and ends with a stopwatch that begins flashing times on Sunday.