I see a lot of new SUVs and cars being offered with much larger tires than the normal 16 to 17 inch tires. What are the advantages or disadvantages of taking a larger wheel size when they are offered for a new vehicle? I have heard larger diameter tires make more noise than the same tread in a smaller diameter is this true? What about differences in gas mileage with larger tires vs smaller (assume same type of tire and tread pattern)?
There are two things that “larger” may mean here. That inch size is the size of the rim. Many cars come with ghetto rims like 20 inch that have very low profile tyres on them so the outside diameter is about the same as the normal tyre would be. Tyres looking like this kind of tyre are often used when racing for addition road feel etc. The problem is first they tend to be easily damaged by that first pot hole and they are expensive, but not nearly as expensive as the real racing versions that are not that easily damaged. Most people would find the ride not as comfortable as the standard design.
The other type are larger tyres along with a higher suspension. Those wheel/tyre combination look more like truck tyres and are good for off roading. Most people buy them for looks. They will cost more and they will reduce your mileage some. They can make access to the passenger compartment more difficult. These tyres often have aggressive tread design and that makes more noise. That is the source of the road noise you have heard about. Getting tyres with less aggressive tread will take care of that.
As Joseph said, road noise is a fuction of the tread design and the car’s inherant design characteristics (resonances, sound insulation).
Many of the new cars with larger rims and lower sidewalls have their spring and shock rates adjusted appropriately and ride great. Mine, with 215x45x17 tires, does. Naturally, the less sidewall there is means the higher the risk of rim damage from potholes.
www.carbibles.com has a good primer on tires. I recommend a visit.