Note:- This does not work for people who prefer light armour.

Become Champion of the Arena and challenge Agronak, the Grand Champion. A.K.A. The Grey Prince.
Talk to Ysabel about the rules and you will learn that you have to loot Agronak's corpse and take his Raiment of Valor and present it to her to recieve your own.
If/when you defeat the half-orc, take his Raiment and equip it, then leave the arena.
DO NOT talk to Ysabel. DO NOT unequip it. If you unequip it you cannot re-equip it.
But it weighs 0 points.
Congratz, you just saved 72 points of weight. (If you take the heavy Raiment from Ysabel it weighs 72 KG...)