You are likely feeling something called tram lining .......where the sharp edge of high performance tires catch the edges of the ruts in the road, causing the tire to actually fall into and jerk out of the rut.
Our ruts up here are caused by both heavy trucks and studded tires. When it rains, you can see the ruts better as they actually fill up with water.
Try driving closer to the center line or closer to the outside edge of the road and see if the feeling goes away.
You don't feel this on a regular tire because the outside edges are more rounded, and ride into and out of the ruts more smoothly, without affecting your steering or forward motion.