You may want to talk to someone about the integrity of the shocks, ball joints, and brakes. It will also hurt you MPG. I am getting ready to go bigger on my tires, and this is what I have collectively been told by all the off roaders around here. I have had several people tell me that the shocks are the most over looked part during a partial build. Not sure why.
It's not really intuitive to think about, but I'll try to explain. Shocks aren't just affected by the vehicle above them, they are affected by the wheel/tire combo as well. The shocks are are generally sized not just for the type of vehicle, but also for your stock tire/wheel combo, specifically the rolling weight of that combo. Larger wheels and tires weigh more, often a lot more. When you hit a bump, the shock tries to dampen/resist the upward movement of the wheel/tire. Bigger wheel/tire means more upward force into the shock. Also, when you crest a hill or bump, the tire begins dropping before the actual vehicle. The shock slows the tire/wheel dropping. B/c the tire/wheel are heavier than stock, the shock is worked harder than it is designed. Now it may only be worked a couple percentage points more than it was designed, but it heats up more and faster than normal which will mean premature failure.
OP, the vibration you are feeling is most likely the tire being out of balance. Also, if you have an independent front suspension, different tire sizes will be less critical, still not ideal, than if you had a straight axle front end.