At face value, the signing of former San Diego Charger Ricardo Mathews to a one-year deal is a good depth move at backup defensive tackle.

In the bigger picture, the Pittsburgh Steelers are moving boldly in a direction that hardly guarantees success -- outside of Cam Heyward and Stephon Tuitt, there are no sure bets on the defensive line.

The Steelers are banking on one of two recent late-round picks -- tackle Dan McCullers and end L.T. Walton -- to emerge as significant contributors to ensure that Heyward and Tuitt get adequate help.

And that’s even if the Steelers draft a tackle early, which is possible, as both coach Mike Tomlin and GM Kevin Colbert feel good about the tackles in this year’s class.

Consider Mathews a fairly even trade-off with Cam Thomas, who is still a free agent, if not a slight upgrade. That leaves the Steelers in the same place as last year, only without now-New York Jet Steve McLendon.

Heyward knows what’s up. The Steelers need productive players in volume, starting with McCullers, who’s an amalgam of raw strength and unrefined football.

“We don’t want to get to the point in the playoffs where we’re gassed,” said Heyward to Steelers.com this week. “If we can get those two guys to step up [McCullers and Walton], I think we’ll be headed in the right direction.”

The Steelers were never going to spend big on this spot, choosing to re-sign a few key in-house free agents and giving Ladarius Green a $4.75 million signing bonus to fortify the tight end position after Heath Miller’s retirement.

Otherwise, they are betting on a philosophical plan to develop the players they already have.

Heyward and Tuitt are evidence of that. Both are top-50 picks and, now, cornerstones on defense. But before Mathews’ arrival this week, Heyward was the only current defensive lineman from last year’s active roster older than 24. He needs more help.

“We’re not going to place an inappropriate weighted need on any particular position,” said Tomlin at the NFL owners meetings last week. “We’re going to do what we do.”

Translation: Young players must do more.