I found a similar but not quite perfect question/answer at:

Possible distance travelled by horse over 6 weeks?

The thread was great, I learned about palfreys and relays, etc. My scenario is a little different. Not a single horse/rider scenario, but a team and carriage. My best guess is that a team of two horses pulling a carriage with four people might travel ~ a few miles per hour. Perhaps 3 - 5 miles per hour. So, for two hours travel time, around 8 miles would be traversed.

Is this right?