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The San Francisco 49ers entered the 2011 season coming off a 6-10 campaign, and lacking a winning record since 2002. Although Jim Harbaugh’s hire instilled some offseason hope following Mike Singletary’s failed regime, you wouldn’t have found many football analysts projecting a playoff trip for the ’11 49ers.

Unless you came to PFT.

Florio last September picked San Francisco to finish as the NFC’s fourth seed, running away with the conference’s west division over then-more-popular picks Arizona and St. Louis. Harbaugh’s club even exceeded Florio’s lofty expectations, going 13-3 and earning a first-round playoff bye before knocking off the Saints en route to an NFC Championship Game berth.

The Niners bring back 11-of-11 starters on a defense that ranked fourth in the league last season, and used the spring to supplement Harbaugh’s offense with explosive skill-position players. With a ferocious front seven on defense and much improved depth on offense, the 49ers will look to finish what they started in Harbaugh’s debut season.

Strengths.

The San Francisco 49ers play violent, unrelenting defense, particularly up front. 2011 Defensive Rookie of the Year runner-up Aldon Smith will switch from sub-package defensive end to starting outside linebacker in 2012, after a 14-sack rookie campaign. Bookend Ahmad Brooks racked up seven sacks of his own last season and appears to be peaking at age 28. In Patrick Willis and Navorro Bowman, San Francisco fields the top inside linebacker duo in the game. Willis’ early-career performance has signaled future Hall of Fame potential. Bowman is relentless in pursuit.

In a true show of the 49ers’ front-seven dominance, Willis, Bowman, and right end Justin Smith all received Defensive Player of the Year votes in 2011. Smith is virtually unblockable and splits double teams. Fellow end Ray McDonald is a quality pass rusher on the left side, and 330-pound nose tackle Isaac Sopoaga anchors the defense on early downs. The Niners played shutdown run defense throughout last season, ranking No. 1 against the run and allowing league lows in rushing touchdowns (3) and yards-per-carry average (3.50).

Offensively, the 49ers are a run-oriented team who play smash-mouth football. They run a powerful man-blocking scheme on the offensive line, looking to beat up opponents in the trenches. Although the 49ers made three big offseason pickups at wide receiver, their intent isn’t necessarily to throw the football with higher frequency. San Francisco will stay balanced-to-run heavy on offense, but wants the pass completions to generate more yards and points.

The one returning skill-position player who already plays at a consistently high level and could get even better is tight end Vernon Davis. Davis is a major factor as a blocker. He was slow to grasp Harbaugh’s offense out of the gates last season, but exploded once comfortable. In the 49ers’ final five games, Davis hung up 28 receptions for 536 yards and five touchdowns — numbers that rival the production of the NFL’s “elite” pass-catching tight ends in New England and New Orleans.

Weaknesses.

Quarterback Alex Smith gained plenty of support during the Niners’ 13-3 season, but he is the weak link on offense. The 49ers know it, as Smith attempted the fewest passes of any 16-game starting quarterback in the league last year. Only the read-option Broncos threw the football less. Harbaugh effectively manipulated Smith with a dominant defense, potent and oft-used running game, and emphasis on high-percentage throws. Smith was — and likely forever will be — a game manager. His job is to complete throws to the open man and avoid turnovers.

Pass protection has been another issue for San Francisco. Smith does bring some of it on himself, but he absorbed a league-most 44 sacks in 2011 and seven more in two playoff games. Third-year right tackle Anthony Davis is still a developing player, and new right guard Alex Boone has never started an NFL game.

Changes.

The 49ers made a lot of them this spring. They signed Randy Moss and Mario Manningham, and drafted A.J. Jenkins in the first round to improve a previously pedestrian wide receiver corps. 2009 first-round pick Michael Crabtree appears to have maxed out as a short to intermediate possession receiver, lacking an ability to defeat coverage downfield. The Niners hope Moss, Manningham, and eventually Jenkins contribute more “splash” plays to a passing game that ranked 25th in 20-plus yard completions in 2011.

As reserves, San Francisco added alleged power back Brandon Jacobs and backup quarterback Josh Johnson. Second-round pick LaMichael James has some Sprolesian potential as a satellite back whom the Niners will attempt to get in space.

The 49ers bring back every starter on defense. They locked up cornerback Carlos Rogers for $29.3 million over four seasons, retained ballhawking free safety Dashon Goldson with the franchise tag, and bucked up to keep outside ‘backer Brooks at six years and $37 million. The biggest change is the promotion of Aldon Smith to every-down player. San Francisco’s defense still has more continuity than any group in the league, and that is an awfully good thing considering their 2011 performance.

Camp Battles.

We haven’t talked much about the 49ers’ secondary, and they weren’t included in either the “strengths” or “weaknesses” portion of this writeup. That’s because the jury is still out on a unit that flashed potential in 2011 but was mostly up and down. Look for second-year man Chris Culliver, a physical press-coverage defensive back, to push Tarell Brown for the Niners’ right cornerback job. Otherwise, the defense is pretty well set.

29-year-old Frank Gore’s role will likely diminish as the season moves along, and victors of training-camp battles behind him may determine who gets more mid- and late-season carries. Kendall Hunter displayed promise as a rookie, but will be pushed hard by Jacobs and James. Anthony Dixon has likely played his last down with San Francisco.

Wide receiver jobs aside from Crabtree are open to competition. Moss will enter camp as the favorite to start at split end after an outstanding spring, but he hasn’t been a reliable contributor in several years. Manningham and slow-starting rookie Jenkins will be there to step in should weak-armed Smith’s sailing downfield passes fail to connect, and Moss’ attitude go in the gutter. More offensive camp battles will take place at backup quarterback — between 2011 second-round pick Colin Kaepernick and Johnson — and guard between Boone and rookie Joe Looney.

Prospects.

The 49ers’ defense is so physical, talented, and field-position altering that it’s probably good for eight wins in and of itself. No one runs on the Niners, and they affect opposing quarterbacks on virtually every dropback.

The offense remains a question mark. There is heavy turnover at the skill positions, and Moss and Manningham are both vertical, stretch-the-field receivers now playing with a quarterback who’s struggled to throw the football downfield throughout his career. Harbaugh must scheme to keep Moss and Manningham productive and content. If not, there is some potential for locker-room implosion.

Ultimately, we don’t see that happening. We see the Niners as a top-five NFL team that is a quarterback away from a top-three ranking.

But if Smith builds on the progress he made with Harbaugh last year, they won’t be a quarterback away at all.

They’ll be a Super Bowl team.