Just recently backed my four year old gelding, and have used a couple of different bits, from simple eggbutts to full cheek snaffle. Was wondering what bits others prefer and why.
So far our ‘steering’ isn’t bad, and we did start off long-lining, so he would have some idea what I was talking about when I actually got on and used the reins. He tries hard, but especially at the canter, we drift far far to the left, which is more of a physical issue, than a bit issue.
As per vet recommendation, due to a few factors, we are concentrating on trot and canter sets out in large fields. I just find it difficult to keep him anywhere close to straight. We wind up drifting the entire length of field so we are nearly on a diagonal the whole time, if that makes sense!
I have been playing around with bits for my 7yo OTTB mare. Although she is older, she was quite green when I got her last fall. I initially had her in a rubber snaffle(D ring) She really chewed on it a lot and kind of cocked her head to the side if I took any contact. I then tried a double jointed happy mouth bit on her, she was a little better (no head cocking), but still quite a bit of chewing. I currently have her in a hollow mouth oval (which is double jointed). She seems to like this the best so far. No head cocking, and minimal chewing. She is not too bad when trail riding moves forward and fairly straight, but in the ring she really falls out on her outside shoulder. When I ride her in the ring I have been doing a lot of walk work to get her to accept contact and leg aids( moving off leg, circling and going across the diagonal etc). I am not sure if I will trail ride in this bit as I don’t seem to have the best brakes with it. As far as the drifting with your horse, maybe take him somewhere that there are wide trails to do some trot work. I find the trail seem to create a funnel type of affect with my mare that draws her forward in a more straight manner.
I have my 6 y/o in a black rubber snaffle currently. When she was started, it was in a loose ring. When I first bought her, I had her in a Happy Mouth, then a french link D at home and at shows a corkscrew then a slow twist. Now she is in the black rubber dee snaffle at shows and at home and she goes amazing in it!
In my opinion, good baby bits are anything with a simple and gentle mouthpiece and no leverage. I think that a full cheek might be good in your case because the sides can help with steering sometimes.
I ride young horses almost exclusively and I can’t say how much I hate rubber/plastic mouth pieces- I really,really dislike them. They are generally bulky, give a “muddled” feeling on the reins (not sure how to describe it), and can encourage the horse to grab and chew which is different from the relaxing soft, movement that is desired.
I really like the Sprenger Dynamic RS bits. They come in 1/8" increments which allow for a better fit than many other snaffles that only have a few size options. The mouthpiece is not bulky and lies nicely across the tongue. Even some of our fussiest babies are happy in these bits. I sometimes put my “busy” mouthed horses in the WH ultra which has a very small roller. The older KK ultras are great too, but I have seen a difference in our sensitive horses when in the RS bits (generally happier in the RS). And all of our babies are started in loose rings (and FYI the Sprenger bits come in a variety of ring diameters) as straightness issues at that stage in training generally starts in the body, not the head.
The mouth is much like the back if the horse. Every horse will be different and the closer to a perfect fit you can get, the better and easier the training will be for the horse. I also see an incredible number of poorly seated bits sitting either too high or low in the horses mouth.
Drifting is just training time… 
Forward straight learning about your aids…
Bits really depend on the horse. I have found this bit is really great for young horses with reasonably soft and smaller mouths.
https://www.smartpakequine.com/happy-mouth-double-jointed-roller-dee-4751p
A lot depends on the horses mouths and what they prefer. My go to, try first bits are always a sweet iron full check and HS loose ring. In your horse’s case I would try to find a full cheek he liked. I find this helps with steering in beginning and it keeps the bit quieter on the young horses mouth. One thing we do is build “chutes” in the corner they are having the most difficulty. You can just lay jump poles on the ground and space them about 8 ft wide. This works as a great visual for the horse so they stay straight and forward through it. Good luck
I like a Fulmer, with keepers and a drop noseband.
Baby horses are incapable of moving in a straight line, until they have built enough muscle to deal with the person on their back.
I tend not to worry too much about straight lines, but instead work at developing lateral suppleness by the use of large circles - 30m size and improving balance with transitions between and within paces. In time he will be able to maintain a straight line.
When I got my 3yo, I rode him in a sweet iron Western Dee with a simple snaffle (two piece) mouth piece. Not the English Dee, the Western Dee, which has bigger rings. It gave him a lot of stability in his mouth and provided very clear steering aids. It was a nice bit for installing steering and breaks and the fundamentals of contact.
Straight lines will come over time. They can’t go straight until they learn how to move up under themselves with their back end, instead of side to side. At four, they’re still figuring out how to move all 4 legs without tripping over themselves, which is not conducive to straight lines. Lots of big loopy circles will be your friends!
Bits don’t make steering, really. The horse’s response to the rider’s seat and leg aids will override the bit every time.
Focus on developing the ability of the horse to follow your weight aid, and you ability to focus on seat/weight aids. Te straight part will come slowly as the balance gets sorted out. In the meantime, shallow loop serpentines, huge circles and trails (if the baby is quiet enough).
I agree that the fat rubber bits are terrible. I hate the feel.
That being said, a D ring can prevent the bit getting pulled through the mouth in an “Oh Sh!t” moment"
Great replies, thanks! i do know the straight lines will come with time, and he is such a smartie, he gets the idea! When we are on the edge of the field, he can more or less go straight forward. But when we are in the middle of the field, at the canter, it’s drift left. At the trot, it just depends which way the barn is
