Armor Cap
Physical damage reduction is capped at 80%. This occurs at 567 displayed armor rating when wearing all four pieces of armor. If you have 100 armor skill (Light or Heavy) and all relevant armor perks, this requires a tempered armor rating of about 135. You can increase your tempered armor rating by 1 roughly every 2 points of Smithing with the appropriate perk, or every 4 without. Therefore, at 100 Smithing you will need 85 base armor with the appropriate perk, which is not achievable without a shield with Light Armor (though Dragonscale comes close at 82 for the set) and requires at least a Steel Plate set for Heavy Armor. With Fortify Smithing enchanted apparel and Fortify Smithing potions you can boost Smithing even further, which can potentially allow any material for which a Smithing perk exists to reach the cap. At the extreme end, you will need about 126 Smithing to make Steel Armor hit the cap, and about 154 Smithing for an Elven set. Unfortunately, Fur, Hide, Studded, Leather, and Iron armors are not affected by any Smithing perks and so cannot be improved as much.
With the aid of enchanting (fortify smithing) and pre-made enchanting and smithing potions, and of course the appropriate armor perks, you can reach the armor cap with any style or type of armor in the game, even hide and iron armor. All without even using a shield.
Shields, spells, and
the Lord Stone can reduce the base armor required to hit the cap even further, but these require more management.