A front five that's 80 percent new

Joe Staley is the only staying put in 2015, while the rest of the offensive line is adjusting to new positions.

SANTA CLARA, Calif. - If the San Francisco 49ers are going to revamp its offense, it has to start with the offensive line. But like everything else this offseason, it's in a transition period.

Amid all the change for the 49ers, from Jim Harbaugh's departure to the slew of retirements, the turnover along the front five might have gone overlooked. Four of the five projected starters along the line will be different from last season in Saturday's preseason opener.

That's significant, because when San Francisco went to three straight conference title games, the talent and continuity along the offensive line played a major role in forming one of the league's best running attacks, which laid the foundation for the offense's success.

In 2012's Super Bowl run, the offensive line consisted of three first-round picks. That number was slashed to one this offseason, with Pro-Bowl left tackle Joe Staley being the only holdover. Left guard Mike Iupati left in free agency to sign with the Arizona Cardinals and right tackle Anthony Davis suddenly retired at 25 in June.

Alex Boone was on that line when the 49ers lost the Super Bowl to the Ravens, but he's changing from right guard to the left this season, playing next to Staley for the first time in his career. That means the three players to his right will be first timers.

"There’s an evaluation going on there," head coach Jim Tomsula said Tuesday.

Halfway through training camp, Joe Looney has seen the most time at center with the starting unit, accompanied by Marcus Martin at right guard and Erik Pears at right tackle.

All three of those players, and even some of their backups, are learning new positions while trying to pick up new offensive coordinator Geep Chryst's offense. Looney spent his first three years of his career playing mostly guard as a reserve, and made his debut at center last December against the Seahawks on the road.

Colin Kaepernick was sacked four times that day, and threw two interceptions with 121 yards passing in the 19-3 loss. Looney drew criticism from former offensive coordinator Greg Roman, who rarely called out players for poor play publicly, saying, "There were some things there that fundamentally he could have done better."

Martin is getting most of his practice reps at right guard, where he hasn't played since high school. But his time at center has increased lately while the offensive line has struggled against the 49ers' blitz-heavy defensive front in practice. Pears is moving back to his natural position of right tackle after playing right guard in 2014 with the Buffalo Bills.

Even Brandon Thomas, a "red-shirt" rookie who missed his first pro season while recovering from a pre-draft knee injury, is playing a foreign position. In camp he's worked primarily at right guard after general manager Trent Baalke said in the spring, he was drafted with replacing Iupati in mind.

That means the 49ers are tasked with finding a five-man unit that works together, with four of those players learning a new position. Not to mention trying to learn a new offense.

"It’s tough," said Pears. "Especially in the NFL, man. It’s the best of the best ... It creates a problem."

The good news for San Francisco is it doesn't play a meaningful game for more than a month when the Vikings come to Levi's Stadium Sept. 14. And that should give the offensive line time to figure things out and get accustomed to their new roles.

"It’s a transition for a few weeks," Staley said. "It’s not something that’s going to take a whole year. Your brain’s kind of used to playing one side, and you’re used to punching with one hand, and kind of leading with one hand. You just got to flip that over. It just comes with time and reps."

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Twitter Mailbag Part II: the secondary

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