What is the range of the Scent ability of animal companions? It's unlisted, but by peeking at the bestiary (and the Gnome's heritage feat) we can conclude that the normal Scent range is 30 feet (probably).
What is the weight of an unconscious character? It's also unlisted, but under the petrified condition we can infer that Medium characters are 8 bulk and Small characters are 4 bulk (though this still leaves me unsure).
What other obscure knowledge is there you've managed to find? (At what point does a Horse become encumbered?)
Riding horses have str +2 and are large (x2 bulk limit), so they become encumbered at bulk 14 (warhorses at 16, because their strength is one higher).
However, as large creatures, they count all bulk 1 items as L, so in theory you could stock a riding horse with 140 bastard swords and he'd still be good. Replace those with longbows and you squish the horse.
This also means that a warhorse can carry two medium people, but only if they are naked and do not have a saddle. A riding horse that encounters this is more likely to bite you in unfortunate places instead.
Edit: Whoops forgot bulk limit.