Justin Smith contract extension: What does it mean for Tank Carradine?

Wednesday afternoon, the San Francisco 49ers announced they had signed defensive tackle Justin Smith to a two-year extension. The new contract will keep him in San Francisco through the 2015 season. Smith remains one of the best defensive lineman in the league, and his absence late last season, and limited health in the playoffs showed how important he is to the 49ers defense.

In his media conference after signing the contract, Smith talked about the endgame of his career. While he is signed through 2015, he stated that he would not go out quietly like we sometimes see with veterans. He wouldn't be a 10- or 20-snap guy at the end. He said he's either going or he's not going, at which point it's time to get a ticket like everybody else.

This will be interesting to follow over the next three years, particularly in light of the fact that the team drafted defensive end Tank Carradine in the second round of this year's draft. The team is always looking for depth, but I think most of us look at Carradine as a potential Justin Smith replacement at some point.

Carradine has yet to practice with the team as he continues his recovery from ACL surgery. He suffered his injury the day before Kyle Williams tore his own ACL. While Williams appears set to be back in time for training camp, Vic Fangio stated that he did not expect Carradine back for the start of training camp. I suspect we'll see him a week or two in to camp, but we'll have to wait and see.

The real question now though is the bigger picture with Carradine and Smith. For now we expect Smith back and ready to roll when training camp starts. Now that he's signed through 2015, the question is what will this mean for Tank Carradine's playing time. While the 49ers haven't revealed their specific plans for the defensive line in 2013, some rotation is expected. I expect to see Carradine and Glenn Dorsey getting some time to spell Justin Smith and Ray McDonald this year.

Beyond 2013 is hard to tell. At what point does Carradine force his way into the starting lineup ahead of Justin Smith, if ever while Smith remains under contract? Smith is now signed through 2015, while Carradine is signed through 2016. The 49ers cannot even begin to consider a contract extension for Carradine until after the 2015 season. It could be a tough negotiation at that point since Carradine may only then be moving into the starting lineup.

That being said, the 49ers could follow the Ray McDonald route if they're comfortable with Carradine's performance as a backup. The 49ers gave McDonald a five year, $20 million extension in 2011, even though McDonald had not been a starter at that point. They liked what they saw, and were prepared to roll the dice on him as a starter.

2015 will be an interesting year for the 49ers. Both Smith and McDonald will be free agents. Smith sounds like he could be retired by then, if not shortly after, and we don't know what the 49ers will be doing with McDonald's contract. There could be some serious shake-up on the defensive line at that point.