Vibration before and after new tires

So this doesn’t happen if you accelerate past 25 mph, then coast back down to 25 mph? No vibration as you coast back to 25 mph? Even when coasting in neutral? hmmm … seems the most likely culprit is some kind of drive-train problem. There’s a lot of possibilities, but having the engine and transmission mounts inspected is a good place to start. Sometime you can notice if there’s a problem by gunning the engine a little while idling in the driveway. Open the hood and watch the engine as you do this. The rotational inertia will cause the engine and transmission to visibly move a little against the mounts. Does it move considerably more than you’d expect from doing the same experiment on other cars?