Changing wheels on a 2000 Lesabra

I recently purchased a 2000 Lesabra limited with around 30K. I love the car but absolutely hate the wheels because they look plastic and fake. A dole eye sore to an otherwise great car. From what I'm reading
this means it's not equipped with some kind of suspension package.
Today while at a junk yard with a friend I noticed a totaled Ultra with a really nice set of chrome wheels that has the Buick symbol in the middle. I can picture them looking fat as hell on my car. I didn't want to seem excited to the yard owner because I figure he'll raise the price if he knows how bad I want these wheels.
My question, my Buick currently has 15" wheels but the Ultra wheels are 16". I know there is a package that puts 16" wheels on a limited but I don't know how much of the package I need. What all will happen if I put the 16" wheels and tires on my Lesabre? Will my speedometer be off? Will the car handle wiered? Are there other parts (in relation to putting the 16" wheels on my car) on that totaled car that I should try to negotiate into the deal? What do you figure would be a fair price?
Also, I noticed this car has excessing left and right movement when you drive over grooved highway where the big road eater scrapes off a layer or two prior to putting down new asphalt. Far more than our other two cars and my wife even noticed. You don't feel it in the steering it is more like the whole car is moving side to side. Is this normal for this type of car?
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Soapm wrote in alt.autos.gm

Can't comment on changing tire sizes. But to the steering, how are the tires. I have noticed that when tires start to wear that they tend to do things like that. If the tires are good, then check the front end alignment.
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I went around to some tire shops and one guy told me that if I up the wheels I can reduce the tire size and nothing else will change. He said if I go with 16" wheels since they have better flavor I can go with 225/60/16 and it will be the same as having 235/60/15 on a 15" wheel. Does this sound right?
snipped-for-privacy@yahoo.com (Soapm) wrote in message

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I'm no tire expert, but that doesn't sound right. I think he meant, increase rim size & decrease aspect ratio ... ie: go from 235x70x15 to 235x60x16 .. tread width would be the same, outside diameter would be 'close'.

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