Barding

All barding encumbrances listed in UA are reduced to 40% of their listed value when equipped. If not being worn by the mount, encumbrance is as listed.Ex1)Here is the reasoning:

Rules for barding were introduced in 19832) and reprinted in UA in 1985. They are basically broken – mainly, the barding is far too heavy. Encumbrance was dramatically increased from the OD&D numbers, to the point where medium and heavy horses may not even be able to move at all.3) This was brought up in Dragon #118, but via a forum submission which was apparently not replied to by TSR.

Barding AC mod AC type Eq. cn. Uneq. cn. Base MV“ and Mi./day (L/M/H Warhorse)
Leather -1 8 640 1600 21/17/15
Scale -2 6 1000 2500 15/15/14
Chain -3 5 1400 3500 —/12/13
Plate -4 3 2000 5000 —/—/12

Don't forget, MV is halved if the mount's first encumbrance threshold has been met. If the mount's maximum encumbrance has been reached, it is unable to move.

1)
Inspired by Dragon #118 Forum.
2)
Dragon #74.