Susanne gave you a pretty good explanation to which I will only add a bit. Quick hitch harnesses, as I understand them, put all the job of moving the cart on the saddle. The shafts can't roll up on the horse because they're attached firmly to the saddle, and the horse pulls from that direct shaft connection and a thin y-shaped breastcollar (the Buxton, isn't it?) holding the saddle in place rather than from a set of traces. A standardbred on the track is going to have no problem at all with that minimalist setup because he weighs 1,000lbs and is hauling a very light sulky with flyweight driver over a smooth track. He accelerates smoothly and slows smoothly with no sudden turns or variety in his terrain. The harness is perfect for what it's designed to do.
Now a mini in the same circumstance can also use that setup and be fine although he's already working harder than the big horse as even with a light sulky he's still probably hauling at least half his own weight, likely a bit more. (That would be, what, about a
500lb load for that same Standardbred?
) That's a lot of work and may not stay comfortable for long with a shoe-string thin load surface. Also consider that the Standardbred is much higher up compared to his load- he's more equivalent to a guy dragging a light sandbag behind him on a rope. The mini is a guy hauling a heavily loaded wheelbarrow behind him- it takes more muscle mass to move something on a horizontal plane than to be able to lean into it from a higher position.
Then imagine taking that vehicle off the track. Suddenly you've got deep footing that makes the cart really drag, rocks to bump over, hills to go up and down, things that may spook the horse into suddenly starting or stopping...picture a Standardbred in racing harness managing two 250lb people overflowing his little racing sulky, driving for an hour or more in circles and figures and at all different gaits, and trying to perform with grace and balance in that circumstance. Do you think he'd do very well? Or would he start objecting as the straps pinched his shoulders, his back got sore from the weight and the load kept slamming forward and back between withers and crupper?
Oh, and don't forget his head is strapped up tight with an overcheck so he can't get his neck down to pull or give his back any relief. I can't help but think that unless he was a very patient, stoic fellow he'd probably start throwing his head and fidgeting and perhaps trying to rear or buck to communicate what discomfort he's in.
Now let's make this even worse by taking it into the real world. Unless you're truly using a racing sulky for your quick hitch, your cart and driver combo likely weighs
the same as the horse pulling it, not half as much. Can you even imagine asking a Standardbred to pull another Standardbred up and down hills in a racing harness?
That is why our very smart ancestors designed different kinds of harness. For a load like that, you're going to use a neck-collar that distributes the load as widely as possible and the horse will be able to get his head down to his knees if necessary to pull, pull, pull. Our minis of course fall somewhere in the middle of those extremes but that's why modern carriage harnesses have been designed the way they are. The saddle holds the shafts up but ideally only supports them, does not have them tied down tightly to the saddle. This allows all the bumps and vibrations to work themselves out without being transferred directly to the horse. There may even be a sliding backband between the two tug loops, allowing them to slide back and forth through the saddle and balance themselves as you go over uneven ground. The horse pulls from traces attached at one end to the nice wide padded breastcollar and at the other to a singletree which moves and protects the horse's shoulders (which admittedly are restricted by the breastcollar) from being jolted as they reach the end of the trace with each stride. There is breeching around the horse's rump which attaches to the shafts and allows the horse to sit down into the weight of the load and hold it back with the biggest muscles in his rump. All of these pieces work together to keep the horse comfortable and enable him to do his job without injury.
The closer your intended usage is to the track, the more suitable a quick-hitch harness is going to be. But if you plan on doing lots of trail drives you'd be better off to "dress for the occasion" as it were.
Show harness, of course, is somewhere in between the two as it's more minimalist and meant for use on a flat smooth surface but does have the breastcollar instead of asking the horse to pull directly from the saddle. (Well, it's supposed to be used that way at least.
) I would LOVE,
love,
love to see a mini roadster horse hitched with a Buxton and quick-hitch though! That would be so incredibly awesome to see and he's not going to get sore just going around an arena with a sulky for a few minutes. It would be fun to have one in parades too as those are on pavement and involve very little hard pulling.
So...yes, you can get one, and no, I wouldn't use one for regular driving unless I lived somewhere very flat and smooth. It's too hard on the horse with a heavy load! What you can do however if you get into serious recreational driving is buy the "quick-release" stuff available for CDE (combined driving event) marathon harnesses. There's a type of tug loop that opens into a cradle you just lay the shaft into and then secure by tucking one strap through a keeper, you can leave your holdback straps wrapped around the shaft permanently and simply snap them to your breeching each time, and the traces only take a moment to slip over the curly hooks a marathon cart has. Hitching doesn't take long when you're using that stuff! You can reduce it to laying the saddle on the back, tightening the girth, buckling the crupper, pulling the breastcollar with traces over the horse's head, and bridling. That's not bad. Then tuck tuck, hook hook, snap snap, one buckle for the overgirth and you're away!
Leia