What are the limitations of a team? As it relates to national titles and the College Football Playoff, what determines a team's ceiling? Talent, certainly. Coaching, of course. While there are all kinds of forces at play that can propel a team to success, very few singular factors can set limitations quite like the quarterback position. In the College Football Playoff era, where it takes two wins against the best in the country to win a title, those restraints are even more magnified.

On the eve of the college football season kicking off in earnest, I wanted to look at what quarterbacks set the speed limits for some of this fall's most serious national title contenders. But first it's important to look at what the precedent is for playoff success under center.

The CFP era has given us 15 quarterbacks (17 appearances) to evaluate among 16 different teams. They generally fall into two categories: bus drivers and fighter pilots.

Bus drivers are capable, they keep a talented roster on the road and do their best not to lose the game. They can look dominant against weaker opponents, but have weaknesses that get exposed in two-game playoffs. They aren't NFL Draft picks, but they're often highly decorated college players.

Fighter pilots can elevate a team, win a game on their own and in the event of a loss, even in a playoff setting, it probably wasn't their fault. Not only are they NFL Draft picks, they're early round guys.

Let's take a look at the crop to make it to the playoff so far.

YearFighter pilotsBus drivers
2014

Cardale Jones*, Marcus Mariota, Jameis Winston

Blake Sims

2015

Deshaun Watson, Baker Mayfield, Connor Cook

Jacob Coker*

2016

Deshaun Watson*

JT Barrett, Jalen Hurts, Jake Browning

2017

Baker Mayfield, Jake Fromm, Tua Tagovailoa*

Jalen Hurts*, Kelly Bryant

*= won national title

In the playoff era, Alabama is the only team to win a national championship with a bus driver at quarterback and among the seven quarterback appearances with my bus driver label, Alabama was home to four of them. Translation: if you're going to be average under center, you'd better have Alabama talent everywhere else and very few teams can replicate that.

As the only non-Alabama quarterbacks with a bus driver's profile, Jake Browning, Kelly Bryant and JT Barrett are collectively 0-3 in the playoffs. On average, they lost by 22 points and collectively their offenses produced 13 points.

So who is going to run up against some limitations in 2018? Who will be out of their element if they earn a playoff opportunity? Let's take a look at the AP Top 15 to determine who can realistically put national championship on their list of goals.

15. JT Daniels (USC) -- He's a true freshman, but he's a fighter pilot. Trevor Lawrence and Justin Fields got all the hype from the 2018 class because for most of the cycle, Daniels was in the 2019 class. But he's every bit the quarterback talent of those two. He has everything Tua Tagovailoa and Jake Fromm had. If USC can get there, he's good enough to win it.

14. Shea Patterson (Michigan) -- He's a fighter pilot with a chip on his shoulder after leaving Ole Miss with some doubters. From a talent perspective, he's one of the best in the country and Michigan has accumulated plenty of talent around him.

13. KJ Costello (Stanford) -- Costello is a bus driver right now. Can he evolve into a fighter pilot this year? I think he's got that in him, but based on what we know, it's hard to put him there yet. Does Stanford have Alabama-level talent around him? I think they do on offense, but defensively, the personnel doesn't look ready to compensate.

12. Brandon Wimbush/Ian Book (Notre Dame) -- Last season was a disappointing year for Notre Dame at the quarterback position. We had high hopes for Wimbush and it just didn't click. He's a currently a bus driver with a missile launcher on his arm and while Notre Dame has some good pieces, the defense doesn't have the freaks to carry this team to a title.

11. Brian Lewerke (Michigan State) -- Lewerke is just another Michigan State quarterback who has steadily developed into an NFL talent. We'll put him in the fighter pilot category, but it feels like 2019 is the more realistic year for national title goals.

10. Trace McSorley (Penn State) -- Fighter pilot all the way for McSorley. Between that, a favorable schedule and a roster that will come of age as the season progresses, national title aspirations are reasonable.

9. Jarrett Stidham (Auburn) -- Stidham is a fighter pilot with a coaching staff that will better know how to use him in Year 2. No ceiling on Auburn.

8. Malik Rosier (Miami) -- Can we even give Rosier a bus driver label yet? It feels like Miami still needs to get this position figured out before it can dream big and the roster is inching closer to that Alabama status. It's just not there yet.

7. Kyler Murray (Oklahoma) -- I don't think Murray is a fighter pilot yet even though it's awfully difficult to label him a bus driver. But that confusion is why I have a hard time seeing this team get any further than it got last season.

6. Jake Browning (Washington) -- Browning is one of the most productive quarterbacks in college football and yet, from a tools standpoint, he remains a bus driver to me. Washington is one of the real risers in college football, and yet from a talent perspective, they're not Alabama yet. Washington is good enough to get the playoffs. I'm just not sure it's good enough to win yet once it gets there.

5. Dwayne Haskins (Ohio State) -- We don't know really know what Haskins is, but I suspect he's a fighter pilot. It doesn't really matter though. The Buckeyes have the talent to win with a bus driver too, and Haskins is at least that.

4. Alex Hornibrook (Wisconsin) -- Hornibrook is the ultimate bus driver. Capable, but that's it. Has Wisconsin turned the corner from a personnel perspective to win a title with that kind of player? Offensively, between the line and Jonathan Taylor, it's there. Defensively, while Wisconsin is really good, you're not getting waves of NFL guys coming at you. It's close, but I actually lean that Wisconsin has a national title ceiling.

3. Jake Fromm (Georgia) -- Georgia is talented enough to win with a bus driver, but I think Fromm is much more than that anyway. Plus, with Fields on the roster, there are two fighter pilots at Georgia's disposal.

2. Kelly Bryant (Clemson) -- Bryant limits what Clemson can do on offense. They are a better team if true freshman Trevor Lawrence can grow under center and I think it's got a better shot at a national championship with the youngster. But if 2015 Alabama can win with Coker, 2018 Clemson can win with Bryant.

1. Jalen Hurts/Tua Tagovailoa (Alabama) -- I'm not even convinced that Alabama has an Alabama-level defense this year with the way injuries have been hitting them. It can win a lot of games with Hurts' limitations, but this may be a unique year that Alabama needs that fighter pilot to win a title and a bus driver won't be enough.