I have tried various ways of enchanting armour to fortify smithing and have found the maximum smithing fortification is 28 on 4 items, which is a total of 112, the items are Bracers, Body Amour, Necklace and Ring. You can buy blacksmith elixers which will give you a further 50% on top. These only work for improving. I have seen through various youtube videos that if you max out your alchemy and have the relevant perks (plus a fortify alchemy set of armour) you can create a smithing potion that gives 140%. So I am now working towards upping my alchemy. You can only get the benefit of one potion btw, so if you drink 10 blacksmith elixers you will still only get a 50% improvement which you get from one potion.