What causes wheel vibration???

I am just wondering what usually causes vibration in front wheels and tires? My front tires make a kind of humming sound at all times above about 20 mph. At all times; accelerating, cruising, and decelerating. When slowing to a stop, it gets quite loud, and the front wheels vibrate. It just doesn't feel good at all.
I have just changed my tire and wheel size. I went from a 235-60-16 to a 275-40-17. On a firebird. The wheels/tires fit fine, there is no rubbing at all. My old twheels/tires were totally silent. But the moment the people at America's Tires put on the new ones, I began to have the problem.

Any ideas?

Wheel vibrations are almost always caused by wheels that are out of balance or out of line. The most likely problem here is that the wheels were not properly balanced by the installer. Another thing is that every time you change tires your are supposed to do a wheel alignment. I would start by getting the balancing cheched and if that doesn't work get a wheel alignment. Good luck and nice car.

OK, if they're humming its probably your new, radical tread pattern. What kind of tires do you have?

As for the vibration when stopping, your brake rotors are probably warped. Did this happen before you got the new wheels & tires? Do you feel a vibration at highway speed? If not, your wheels are probably well balanced.

I have had absolutely NO problems before the new wheels and tires. It was the moment they were done and I went to drive home that I got the problem. I first heard it when I hit about 15 miles per hour. I could just hear the noise. And that is at any speed I go. Now when I slow down and stop, I can feel vibration.

I immediately called the tire shop, and they told me to bring the car back. They said there's nothing they could do, it was the tires. They said it's because the tire's worn. (The tires aren't new, but they still have a lot of life left) This just seemed like total BS to me, because the old tires I replaced were VERY worn. They never made any noise. I told them that doesn't really satisfy me, so they re-balanced them for me.

So. the new tires ARE balanced. I'm just thinking of taking the new tires off and putting the old ones back on and driving in it for a minute to see if the problem is still there. If it IS still there, then that tells me that they have damaged something, and they're gonna pay to have it fixed. If the problem's gone, then I guess I can assume it IS the tires.
But this will mean my tires won't be balanced, right?

So what do you guys think??

Now here are some facts:
There are many things that can cause the vibration which you are experiencing, some of which have been mentioned, some overlooked. So here's my take:
There are several areas that you should inspect for possible problems first.

#1.) retainer clips on the studs of your car
These clips look similar to lock washers and are installed on cars when they are being assembled. Most aftermarket wheels do not have the same recess machined into them to accomodate these clips.
#2.) Are the wheels HUB centric or LUG centric?
Lower quality aftermarket wheels are not designed to distibute weight onto the center hub of a car but, use the lug nuts or bolts to center the wheel and carry the load. Many times the wheel is not exactly centered with this type of wheel. Always get hub centric wheels which can use hub centering rings or be machined to fit exactly.
#3.) Tire balance
A balance vibration usually comes and goes at certain speeds.
#4.) Bent wheels
A bent wheel can cause a major vibration. Since you mentioned new wheels this is not likely
#5.) warped brake rotors
Usually only detectable when braking but, exteme conditions will vibrate continuously. You mentioned that the problem is only with your new wheels so , not very likely
#6.) Worn suspension parts
Tie rod ends are the most common part to cause vibrations from this area and the wider front tires would make it more noticable. The easiest way to determine if this is the problem does the problem go away when slightly turning.
#7.) tires out of round
This is not very likely but, does occur accationally

This is where you need to start. I would think that you will discover the cause of your problem if you look into all of these things.

Now tire noise ...
Most tire noise is created by the tread blocks of the tire slapping the ground. Some tire are worse than others. If the car has any tire wear problems or the infaltion is not maintained properly the tires wear in a fashion that enhances the wear of the tire into a cupped or feathered wear pattern that is very noisey. Some tires like the Yokohama A520 or the Pirelli P7000 Super Sport are always very noisey

Wow, I appreciate that very informative reply.

Where I am at now: I have taken off the new wheels/tires from the front, and put the old ones back on; mainly to see if the tire shop has damaged something. I drove the car and it was silent again. So, it appears that nothing up front was damaged, and the wheels or tires themselves are causing the problem.

Here is what I think it may be: The tread wear. When I took the new tires off (I say "new", but they're actually used. Just not nearly as worn as the older ones) they are worn a little on the inside. The old tires are actually worn on the OUTSIDE. So it appears that my car tends to wear down front tires on the outside, and the new tires are already worn on the inside.

I think that's where the noise and vibration comes from.

What do you think?

The noise could be because of the wear issues with your tires but, the vibration is most likely another cause othe than tire wear.

Well, from your "10 causes" of tire noise, the only thing OTHER than tire wear would be a bent wheel, because everything was fine once I put the old ones back on.

Bent wheels could be detected from another car following after you
In case of out-of-balance vibration comes at certain speed e.g. 60-65mph and goes away when exceed 80mph. kind of mechanical resonanse