(This question is research for fictional/simulation-game purposes. The context is medieval cavalry – i.e. men trying to fight from horseback, some of them in heavy armor.)

I am interested in any answers anyone might have to any or all of the following questions about what happens when someone who is heavier than is easy for a horse to carry, tries to ride that horse, and how it affects the horse’s speed and and control, and the rider’s stability.

Will horses tend to balk, refuse, resist, or even kick someone too heavy trying to mount and ride them?

If you do manage to mount and ride a horse beyond what it can do more more than a few minutes, what are the effects in terms of how much slower it could run and how rough the ride would be?

Is there a point (as you add weight) beyond which a horse suddenly goes from being able to be ridden for hours, and then with just a few more pounds, it would have to stop after a few minutes? Or is it more gradual? (So for example, if a the most a horse will bear for hours is 240 lbs, and someone mounts with 260 lbs, how long would they tend to last? 280 lbs?)

If a horse’s limit for sustained riding is say 240 lbs, how much would the limit be for a willing horse to be ridden for a few minutes? 280? 360? 400?

Can a horse run notably faster with no rider than they can with even a light jockey?

How much slower can a horse run with a rider who is about the most it’s happy carrying, compared to how fast it can run with no rider, or with a very light rider?