Don't take it the wrong way, it's about getting you up and down the trail with out damage, breakage, or injury. Neither of these trails is very friendly toward stock rigs. Iron Chest requires 33's and 4.5" of clearance. Grizzly isn't as bad, but even well built rigs can get into trrouble by taking a bad line.
There are few things worse than finding a broke down, stuck stock rig on a trail that the driver should never have been on in the first place...one of them is being the driver of the broke/stuck/ill-equiped rig.