Allen Park — Lions safety James Ihedigbo, who was with the Ravens from 2012-13, recalled what it was like preparing for the Super Bowl against the 49ers after the 2012 season.

"Just their whole like mindset of their team went to physical, in-your-face, ground-and-pound makeup," he said.

Some of that identity came from coach Jim Harbaugh, who was 44-19-1 in four seasons at San Francisco that included five playoff wins from 2011-13. But after an 8-8 finish in 2014, the 49ers fired Harbaugh and handed the reins to Jim Tomsula.

"You can even still see the remnants of that (identity) on film," Ihedigbo said. "They're going to compete, regardless of their record."

This season, though, the team Ihedigbo sees competing has struggled. The 49ers are 4-10 and a minus-137 point differential, worst in the NFL. And that's the team the Lions face Sunday at Ford Field.

Although Harbaugh, now Michigan's coach, put his mark on the 49ers, Lions players believe the team's issues this year are due more to an abundance of personnel turnover.

Linebackers Patrick Willis and Chris Borland and defensive lineman Justin Smith all retired. Running back Frank Gore and left guard Mike Iupati left in free agency. Right tackle Anthony Davis announced he was taking a break. The team cut linebacker Aldon Smith in August after a series of off-field issues. And like other teams, injuries have piled up, including to former starting quarterback Colin Kaepernick.

"I don't think, in terms of what they want to do and their identity, is any different," Lions defensive coordinator Teryl Austin said. "I just think they have a lot of different players. … You're not going to get rid of that identity in one year."

Austin described the 49ers as "tough" and "gritty," and said the offensive line is really good, something that was a staple under Harbaugh.

Losing so many starters is hard for any team to overcome, and even though the 49ers changed coaches, quarterback Blaine Gabbert said the approach in the locker room hasn't changed.

"Our team has got a great vibe," he said. "We've got a locker room full of great people, we enjoy being around each other and we play for one another. That's the biggest thing to keep that locker room, and keep this team, together is you've got to enjoy each other, and that's how our team is."

The 49ers haven't had much to enjoy on the field. They're 1-6 on the road, and even though the franchise has won 14 of its last 15 over against the Lions, this team is far different from many of the recent ones.

San Francisco ranks 32nd in scoring (14.4 points) and total offense (291.4 yards). They're 23rd in rushing offense (93.9 yards) and 30th in passing (197.5 yards). In his six starts, Gabbert has seven touchdowns, six interceptions and an 82.8 passer rating that ranks 30th in the league.

The once-feared defense has fallen off, too, as the 49ers rank 18th in points allowed (24.2), 27th in total defense (390.3 yards) and rush defense (128.6 yards) and 26th in pass defense (261.7 yards).

During Harbaugh's four years, San Francisco had a target on its back within the West Division.

"It naturally just became our rival game," said Lions receiver Golden Tate, who was with the Seahawks from 2010-13. "It was a very physical, intense game. I think it was just because both teams were really good at that point, though."

The 49ers had a strong start this year with a 20-3 upset victory over the Vikings. Second-year running back Carlos Hyde had 168 rushing yards that game, but has failed to reach 100 yards in any of the next six games and is now on injured reserve.

So, even though Harbaugh is gone, there are plenty of other reasons the team has struggled.

"I don't pay much mind to any of that," Tomsula said. "Obviously, Jim Harbaugh, what he's done in football, he's done great and much respect to that. But I'm not trying to be anybody but me."

49ers at Lions

Kickoff: 1 p.m. Sunday, Ford Field, Detroit

TV/radio: Fox/97.1

Line: Lions by 9½

Records: 49ers 4-10, Lions 5-9

Series: 49ers lead 36-26-1