Nick Mangold's future the focal point of Jets' O-line rebuild

With free agency approaching (March 9), we're analyzing the biggest needs on the New York Jets' roster and examining possible upgrades:

Position: Offensive line

2017 cap hits of top returnees:

Pending free agents: Ben Ijalana, Wesley Johnson (restricted).

Key stat: A good way to measure the run-blocking strength of an offensive line is how it performs on first down. The Jets didn't fare well, averaging only 3.8 yards per rush (21st in the NFL).

Money matters: They began the offseason with a $42 million cap charge for the line, a ridiculous amount of overspending. Since then, they've lowered the number by $14.5 million, releasing Ryan Clady ($10 million savings) and Breno Giacomini ($4.5 million). If Mangold returns, he probably will have to take a pay cut. His base salary is a non-guaranteed $6.1 million, plus another $600,000 in bonuses.

Big picture: The Jets took care of a major piece of business by signing Winters to a four-year, $29 million extension. They're set at guard with Winters and Carpenter, but everything else is up in the air. Let's start with the tackles. They have no experienced left tackles under contract, and right tackle belongs to Brandon Shell and Brent Qvale, neither of whom is proven. The big question involves Mangold, one of the best centers in franchise history. Mangold, 33, is a second quarterback on the field, but he missed eight games with a serious foot/ankle injury that wasn't healing as quickly as he had hoped. It would be a painful cut, but the Jets could end up cutting their longest-tenured player. By opening day, the Jets could have three new starters.

Free-agent market watch: Ricky Wagner (RT), Andrew Whitworth (LT), Russell Okung (LT), Matt Kalil (LT), Riley Reiff (RT), Andre Smith (RT), Mike Remmers (LT), Byron Bell (RT), Kelvin Beachum (LT), Joe Hawley (C), A.Q. Shipley (C).

Also could become available: Austin Howard (G/T), Sebastian Vollmer (RT), D.J. Fluker (RT).

The game plan: The hunch is the Jets are eyeing a three-pronged overhaul: Sign a left tackle (Ijalana is a possibility), draft a left tackle in the second or third round and release Mangold, handing the center position to Johnson. He's not as sturdy at the point of attack as Mangold, but Johnson can function in a zone-blocking scheme. Shell gets first dibs at right tackle. Look, it's not the ideal plan, but it's a start. It could take a year or two before the line is up and running at peak efficiency.