When driving a pair, the reins do much more than simply connect the driver’s hand to the horses’ mouths.
The coupling reins determine how the two horses share the work, how straight they travel, and whether one horse is allowed to lean, rush, or hide behind the contact.
In theory, a pair should pull evenly, stay parallel, and move forward with their heads correctly aligned. In reality, very few pairs are perfectly equal. One horse may be more forward, more sensitive, stronger, lazier, heavier in the hand, or there may be physical differences.
This is where correct coupling becomes essential.
What are coupling reins?
In a pair rein set, the main rein runs from the driver’s hand to the outside of each horse’s bit. A shorter rein, the coupling rein, crosses over and attaches to the inside of the opposite horse’s bit. This is what “couples” the two horses together. Because the inside coupling reins cross over, they travel a longer route than the outside reins. For this reason, they must be longer than the outside reins. In the Achenbach system, the inner coupling branches are usually about 12 cm longer than the outer branches – depending on the type of horse/pony you are driving. This allows the horses to remain straight without being pulled toward each other. If the coupling reins are too short, the horses’ heads are drawn inward. If they are too long, the pair may spread, drift, or fail to respond evenly. Correct adjustment keeps the horses parallel, forward, and comfortable.
Start from neutral
A normal starting point is a symmetrical setting: both horses taking an equal contact, both heads straight, and both mouths receiving the same level of guidance. From there, the driver observes. Are the horses travelling straight? Does one lean on the pole? Do heads turn out or in? Does one horse avoid the contact while the other does all the work? The reins should then be adjusted to correct the cause, not simply the visible symptom.
When one horse is more forward than the other
A common mistake is to try to “hold back” the more active horse and “pull” the slower one forward. That usually creates tension, crookedness, and resistance. Instead, the keener horse may need to be regulated more softly and consistently, while the lazier horse must be encouraged to step into the contact and take its share of the work. The whip, used correctly and quietly, is part of this.
Coupling rein adjustments are not a substitute for driving skill.
The general principle is simple: The horse that wants to do too much should not be allowed to dominate the pair. The horse that wants to do too little must not be allowed to hide. This may mean shortening or lengthening the coupling branches by one or two holes, depending on the horse and the situation. Even a small change can make a large difference. Basically, when the coupling rein on one horse is lengthened the other is made shorter with the same number of holes. When the heads are not straight If the horses’ heads turn toward each other, the inner coupling reins may be too short. If they turn outward, the inner coupling may be too long, or the outer rein may not be doing its job correctly. It is important not to confuse a head position with true straightness. A pair can look “arranged” in the mouth while still travelling crooked through the body. The driver should look at the whole picture: shoulders, pole position, traces, rhythm, contact, and willingness to go forward.
Adjust, then drive
Correct coupling is not a fixed recipe. It depends on the horses’ size, temperament, mouth sensitivity, experience, and the work being asked of them. A setting that works for two steady horses may be completely wrong for a nervous horse paired with a lazy one. The goal is not to force both horses into an identical frame. The goal is to help them work as a true pair. A well-coupled pair feels balanced in the hand. The contact is alive but not heavy. The horses remain straight without constant correction. The driver does not need to fight one mouth while pushing the other horse forward every few strides.
A practical reminder
Before blaming the horses, check the basics: Are the reins correctly assembled? Are the inner coupling reins longer than the outer reins? Are both bits suitable and correctly fitted? Are the traces even? Is the pole position correct? Is one horse physically stronger, more sensitive, or less confident? Is the driver using the whip as a clear aid, not as punishment? Good coupling does not replace training, but bad coupling can make good training almost impossible. In pair driving, a few holes on a rein can decide whether the horses work together — or spend the whole drive negotiating against each other.
Source/inspiration: principles from Max Pape and the Achenbach system of pair driving reins.