What was the exact function of the lance rest?

Did it just keep a heavier lance in balance or did it also help to withstand the impact when a target is hit?

How does it generally feel like if you hit something with a couched lance? How you spread the force? I think it could easily end up in burned fingers if it just depends on the grip of your hand.

The rest helps support a heavy or heavily balanced lance, and does also make it harder for the lance to be pushed back on impact. Once the arret came into use in the 15th century as part of the "sportification" of jousting, lots of other things appeared that might not be used in battle but were appropriate for a sport. For example, the grapper, a ring of leather or wood behind the hand grip, that further prevented the lance moving on impact.

This is not always a good thing, as it is sometimes useful to let the lance slip or be pushed through the hand in order to keep a seat.

The couch is only partly about holding the lance with the hand, most of the support comes from the clamping action of the upper arm. You won't see this done at Medieval Times and the like, because they don't want that much impact.

Most of the perceived impact is from the incoming lance hitting the shield in IJA jousting (breakable balsa tip, solid lance behind), which is spread through the shield and breastplate behind, so ends up feeling like a quick but solid thump on the shoulder. Big hits happen, when the lance body digs into the shield (we use the encranche for a better rein hand position). Also there is a lot of adrenaline happening, and looking at video I realise some hits are a lot bigger than they felt. Finally, just as in the late middle ages, there are different approaches and rule sets for jousting among different groups, so trying to answer more detailed questions on technique could quickly become bogged down in technical details.

The question I have about them is which part of the lance rests on it? I have trouble reconciling the positions of lance rests I've seen on extant breastplates with the posture of a couched lance.

The proper name for the so-called lance rest is the "arret de cuirass", that is, the arret fixed to the breastplate.

In war, where the arret originated in the late 14th century, the arret is not simply a "shelf" by which a heavy lance is supported, but a hook on the breastplate, creating a means of force transfer of lance impact to the cuirass.

The arret de cuirass is paired with the arret de lance and the two together transfer the impact of the lance to the breastplate (or cuirass; breast and backplate together), so the hand and arm doesn't have to take the force.

Either of the above can be used separately and will partially serve the same function, but usually both were used together.

In the very late 15th century, arrets de cuirass were combined with a hook or queue projecting rearward from the arret de cuirass to help support the very heavy lances developed specifically for the joust. These were never used in war, but were specialized equipment for sport only.

The word "arret" means to 'arrest', that is to contain the backward motion of the lance on impact.

Without an arret, either on the lance or cuirass, on a strong impact you have a recipe for a broken hand or at least thumb (been there, done that, got the tshirt, ----not pretty).

So, what precisely is the difference between a fewter and an arret?

Oh, I should have mentioned that the arret de lance is basically a ring just behind the lance grip, sometimes friction fit to the taper of the butt of the lance, sometimes nailed or riveted on.

The area just behind the lance grip is what contacts the arret de cuirass, so your hand is just forward of the arret de lance.

Fewter........hmmm. I've read the term somewhere, but can't recall what it refers to. I think it might be the arret de lance. I'll see if I can find a reference in my books tomorrow at the shop.

On "Fewter"...

A brief check in Barber and Barker's "Tournaments" yields one reference to an 1168 encounter between the Count of Flanders and Godefroi Tuelasne, where the latter was struck by a blow "from the fewter". The authors state that the term "fewter" in appears in later texts, but given the early origin of the term, during a period where plate armour was only just beginning to be seen and arrets de cuirass were only a glimmer in the armourer's eye, it's unlikely "fewter" refers to the hook on the breastplate. Simply because proper breastplates didn't really exist yet.

It could possibly refer to the arret de lance, which is a device seen much earlier than the arret de cuirass.

Barber and Barker speculate that it could simply refer to the "couched lance", which is certainly also possible, given that the idea of a lance couched tightly -under- the arm was a relatively new idea in 1168, because previously the lance or spear had been held in the hand alone above the head or to the side.

Fewters appear a few times in a translation of Chretien de Troyes romances, which is what lead me to ask about them. Whether or not they were actually called "fewters" in the original text, or if a different term was used, is not known to me.