I'm writing a story set in the medieval era, and it wouldn't be a real medieval story without dealing with the nightmare of the logistics of medieval travel, nor would it be a medieval story without plenty of that said medieval travel. I know that traveling in medieval times was slow, and I've done my fair share of research about it. In every place I've looked for that research, sources always talk about speed in good conditions. But I'm writing a story where characters travel in bad conditions. How much would these conditions slow them down?
The specific example of this is that I'm writing a scene that takes place in the middle of October. Two characters are riding down to a nearby city that is about 45 miles (70 km) away. They each only have one horse, so from my research, the journey would take in good conditions about a day and a half if they stop to sleep through the night. However, this is the day after a rainstorm. While it is no longer raining, the characters are traveling on dirt road that became very muddy after the rain.
I also have some travel scenes in winter. With a large group of people, I'm not sure if my characters would stop for the winter or continue moving. They're walking on foot, and I don't know how the snow would slow them down if they kept moving.