Ryan Van Bibber from Turf Show Times also contributes at SB Nation NFL and has spent part of this offseason looking at various positional units. This past week he put together a rundown of the various cornerback groupings in the NFL and ranked the 49ers sixth behind the Jets, Ravens, Eagles, Cowboys and Falcons.

The 49ers head into camp with the potential for a fairly deep group of cornerbacks. Carlos Rogers and Tarell Brown emerged as the starters, but Chris Culliver put together a solid rookie season, in spite of having to make the conversion from safety to cornerback as a college sophomore. Tramaine Brock has quietly worked his way up through his first two seasons with the team and the team added Perrish Cox in free agency.

ESPN's Mike Sando took a look at some pertinent position battles across the division and specifically addressed the 49ers nickel back battle. Culliver secured the role last season, but he faces fresh competition from Cox. Given the number of spread-type offensive sets mixing in more and more receivers, both Cox and Culliver could see a solid amount of playing time this season.

The 49ers used their nickel defense more frequently than their base defense, so the third corner is quite important. Culliver would seem to have the momentum for the job, particularly with Perrish Cox sitting out last season. Whatever the result for the third, fourth and fifth cornerbacks, the 49ers have done solid work developing a strong rotation of cornerbacks.