When people add coaches, carriages, wagons, and carts to their stories, they often do enough research to find out they may have something called “brakes” and then treat them largely as autos or trucks with horses up front. (Less often, mules, donkeys, camels, zebras, oxen, elephants, or carabao, not to mention moose, caribou, goats, or dogs for motive power.)
In an auto, you can be zooming at freeway speeds, stomp the brakes, and come down to a complete stop. But auto brakes are complicated and highly engineered, even before they were computerized. You have the force multiplier of hydraulic systems in power brakes. You have the brake shoes exerting friction against the whole brake drum.
On a carriage, you have a pivoted stick exerting friction against several inches of the iron tire on a four-foot-high wheel. That’s all.
Let’s get the variations that make no difference brushed aside and call it a horse-drawn coach. Think of it as a British mail coach or a frontier stage coach or a polished private coach – doesn’t matter. What matters is that none of these can be stopped at any notable speed by the mechanical brake.
What stops them is the same animals that pull them.
But any team, to be able to stop a coach in motion, has to weigh what the loaded coach does, or more. Simple physics, fairly obvious, but most people just don’t think in non-auto terms. That’s why one-horse carriages are slight and small. It has to be light enough for one horse to halt.
This is done, not up at the collar, but by a strap that goes behind the horse’s rump. On a sudden stop, the team practically sits back into this to pit their weight and slight traction against the mass of the coach and its speed.
The brake helps a trifle to slow one front wheel. That’s all. If you apply it too steadily for too long, instead of pumping it, friction will heat the iron tire and can set the wheel afire. This still happens, usually with panicky truck drivers who just stand on their brakes. Out by Ko Olina we once had to pass a tractor-trailer cheerfully blazing on the shoulder and sending clouds of tire smoke into the sky.
The brake also adds the final halt to a coach when you want to stop precisely. It’s good to set when the driver climbs down, in case there’s any slope, but then he also chocks the wheels. It needs to be set when the team is being changed.
So you can’t stop a runaway team by leaning on the brake: if it isn’t wet, the tire heats and the wheel combusts. Or the brake shoe does. Or the brake lever snaps.
In hilly country, extra horses will be put onto teams, not so much to help pull uphill as to have the weight to brake on the downhill side. Then you have loaded coach, speed of movement, and the pull of gravity trying to overwhelm the weight of the team to create a runaway coach.
Runaway coaches were properly dreaded. The coach builds up speed. The horses can’t stop it, and in panic try to outrun the pressure on the braking strap. The coach goes faster, weaves, bobs, and swings, and is very likely to tip over on its own, even if it doesn’t hit a ditch. People on the outside get ejected. The wooden body collapses. Those who don’t die immediately may die of exposure and slower injuries. Others may be left permanent invalids or cripples.
In short, lots of plot possibilities if you want them. Just use brakes properly, remembering the team is a big part of the braking system.
(If there’s nowhere to add horses, then you spend the whole trip with enough for the hilly sections and on the flat they all just do less work.)