CFB's top QB depth charts

Johnny Manziel looks to repeat his 2012 Heisman-winning campaign this season. Soobum Im/USA TODAY Sports

Editor's note: This article was adapted from Phil Steele's college football preview magazine, which is available here.

When ranking the top individual position units for my 2013 preview magazine, I took into consideration the talent level and production of the starters and also the overall depth of the unit.

There is no position group I rank where the starter has more influence on my rankings than at quarterback. For most teams, the starting quarterback takes roughly 90-95 percent of the snaps, while other positions have multiple players on the field at the same time and split the reps more evenly.

With that in mind, here is how I rank the top 15 QB depth charts in the country for the 2013 season.

(Author's note: If you are unfamiliar with some of my abbreviations I use below, the "PS" number assigned for each player stands for where I ranked that particular player at his position coming out of high school.)

1. Texas A&M Aggies

Johnny Manziel won the Heisman Trophy last year and clearly deserved it, throwing for 3,706 yards while completing 68 percent of his passes with a 26-9 touchdown-to-interception ratio. He also rushed for 1,410 yards (7.0 yards per carry) and 21 touchdowns. What puts the Aggies over the top is the fact that Manziel was not even the starter out of spring last year. Matt Davis (PS No. 6) and Matt Joeckel (PS No. 53) provide depth.