Given how many dogs I see attempting to go under, or to the side of a tire jump, I would have to say no, it’s not obvious to a dog!
In my experience, shaping the tire leads to very consistent tire performance, though it takes a little longer to train than other methods. Begin by laying your tire flat on the ground, and reward your dog for interacting with it – think box games. Then, only reward your dog for putting their front paws in. At this stage, lift one edge so the tire is at an angle. Continue to reward your dog for their front paws through. Eventually you will raise it so that it is perpendicular to the ground and you can reward your dog for going through the tire!
Place the tire in the frame, and continue to reward the behavior of going through the tire. Once your dog is consistent, you may name the behavior and start raising the tire to be a jump. Be careful not to raise your tire too slowly or too quickly, because if you take too long to get to the full jump height your dog may develop crashing issues. If you are too fast, they may attempt to go under. If your dog is at any time improperly completing this obstacle, go back a step.
Remember to consistently reward this obstacle’s performance, so your dog will learn to enjoy it, and more importantly, realize the rewards of jumping clear through the circle.