i decided to crunch some numbers for the salt trade:
a horse carriage weight limit is about 5444Kg (or 12000 pounds), 97992Kg(18*5444) total
average consumption of salt in medieval times is 20g per person per day(for harbour cities it is 100g, but i can't say that it is a harbour city, so i take 20g), considering the importance of this city i'd say that the population is about 20000 people, so we get 400Kg per day (20*20000=400000g)
with this info we get (97992/400)=244.98245 days of normal salt consumption, less considering weight of a wood crate(23 crates per carriage illustrated, but i need their dimensions to know their weight), and even less with the horse's drawing limits(average horse can draw about 5 times its own weight, assuming that these horses are Warmbloods(400-700Kg) or Draft horses(800-1000Kg) the limits would be about 2000-3500 and 4000-5000 Kg respectively, but once again there's no info of that kind)