Grant Cohn: 49ers’ third exhibition may answer questions … or not

The 49ers’ preseason game Saturday against the Denver Broncos almost matters. It’s the third preseason game, the dress rehearsal. Both teams’ starters probably will play the entire first half so they can get in rhythm and feel confident for the regular season.

Here are the top-three things to watch about the 49ers.

1. The first-string offense

Twelve teams have yet to score a touchdown with their starting offenses during the preseason: Bills, Redskins, Giants, Bears, Jaguars, Chiefs, Rams, Panthers, Cowboys, Seahawks, and the Broncos and 49ers.

Of those 12 offenses, only three ranked top 10 in scoring last season - Dallas, Seattle and Denver. We expect each of them to score a touchdown this weekend.

Do we expect the Niners’ first-string offense to score a touchdown Saturday?

Why should we? Through two preseason games the only starter playing well on offense is running back Carlos Hyde, who’s averaging 5.3 yards per carry. He seems ready for the regular season.

Everyone else seems stuck in minicamp, especially starting quarterback Colin Kaepernick. He has completed just three passes, none to his new big-play receiver Torrey Smith.

But don’t put all the blame Kaepernick. The Niners’ offensive line can’t protect him. According to Pro Football Focus, Kaepernick has faced pressure five of the nine times he has dropped back this preseason - more than 50 percent.

Kaepernick is a quarterback who often holds the ball too long in the pocket, and now he has no time to throw.

Is this offense a disaster waiting to happen?

2. NaVorro Bowman’s endurance

For the Niners to make the playoffs, NaVorro Bowman has to take them there. Simple as that. Bowman is a three-time All Pro inside linebacker, maybe the best defensive player in the league and certainly the best player on the team when healthy.

Last week against the Dallas Cowboys, Bowman played three snaps - his first live action since tearing his ACL and MCL in February of 2014. And Bowman was terrific those three snaps against Dallas. He made tackles on all three plays, and two of the tackles resulted in losses. He looked like the old Bowman.

After the game, we read all about the return of Bowman, how he picked up where he left off like the injury never happened. Like he’s a superhero or an alien from another planet.

The man played three snaps. Not four. Not five. Three.

Great for Bowman that he can play well for three snaps. How about a whole game? Can he play 70 snaps? Eighty snaps? How sore is his knee going to feel in the fourth quarter? Or the day after a game?

Will the Niners even use Bowman for entire games, or will they take him off the field during passing downs and use him as a run-stuffing specialist?

Can Bowman even make it into the second quarter against the Broncos, or will the 49ers continue to protect him?

Bowman still has a lot to prove.

3. The new dime defense

Watch closely when the Broncos’ offense is facing third-and-long or operating the two-minute drill - obvious passing downs.

In those situations, the Niners are using a dime defense - three cornerbacks, three safeties and only one inside linebacker. This is new.

Under head coach Jim Harbaugh during passing situations, the Niners almost always used a nickel defense - three cornerbacks, two safeties and two inside linebackers. The Niners did this because one of the inside linebackers - Patrick Willis - could cover any tight end in the NFL and also could tackle a running back. So the nickel defense was strong against the pass AND the run. It may have been the best nickel defense in the NFL.

But Willis is gone, and his replacement is Michael Wilhoite, whom the coaches seem not to trust in coverage. They take Wilhoite off the field and replace him with a safety - rookie second-round pick Jaquiski Tartt - when they anticipate a pass.

Tartt wears No. 29. Watch for him. It’s easy to mistake him for an inside linebacker because he lines up next to Bowman, but Tartt is no inside linebacker. He’s the dime back. He weighs only 221 pounds. Willis weighed 240.

Using Tartt is a clever way to replace Willis on passing plays, but not on running plays. The dime defense is not built to stop the run. It simply isn’t big enough. It’s a speed group.

Which could lead to problems. What happens if an opposing team passes to its tight end on first-and-10 when Tartt isn’t on the field? Can Wilhoite cover the tight end? If not, what will the Niners do? Will they let the tight end have a big game, or will they adjust, replace Wilhoite with Tartt. If they do that, the running back will have a big game because Tartt is not strong enough to consistently stop him.

The Niners face a lose-lose choice, a choice they never faced under Harbaugh. Stop run. Stop the pass. Don’t stop both.

The Broncos may not be able to force this lose-lose choice on Saturday-they don’t have a good tight end. But this issue will come up again and again in the regular season. When it does, will the Niners have a solution?

Grant Cohn writes sports columns and the “Inside the 49ers” blog for The Press Democrat’s website. You can reach him at grantcohn@gmail.com.