I have a VW Jetta Sportwagen with 17" wheels and Conti 225/45R17H low profile tires. Ever since I first bought the car, i have been annoyed by the higher-than-expected road noise. Perhaps this is caused by the tires, perhaps by the body characteristics of a wagon, perhaps it’s just the noise anyone would get from a Jetta chassis. The tires are due for replacement soon, and I’m wondering if I would experience a meaningful reduction in road noise if I switched to 16" wheels and less sporty tires? It wouldn’t be cheap to replace wheels and tires, but it could be worth it if the noise level drops significantly. Has anyone made this kind of change and noticed a real difference? If the wheel change is not worthwhile, which 17" tires would be a quieter choice?
The diameter of the tire shouldn’t make much difference in road noise, but the aggressiveness of the tread and the composition of the rubber will. Tirerack.com has consumer information on noise as well as traction and so on and would be worth a visit.
I think 16s with a quieter tire because you’ll have more sidewall to absorb the road bumps. I think Michelin and Goodyear make some quiet tires, you might check out your options at tirerack.com.
I have 16’s on my Jetta (01), and although there is road noise, it’s not excessive. I can have a quite normal conversation with the wife at 85. Granted, she’s normally got her eyes glued to the road and hanging on at that speed, but we don’t have to talk loud or anything. 
Noise level is a very personal thing, though. Without a DB meter, I can only give you that impression.
You can go to tirerack.com and enter your vehicle. From that, you can compare all the tires that currently fit your vehicle and check how they do for road noise, in the opinion of buyers that have rated the tires.
The impression of of the noise level can be more important than the reading on a dB meter. It has to do with the frequencies generated. Unless you et a spectrum analyzer, a dB meter just gives you total noise. Its the higher frequencies that are the most annoying and cause the most damage to your ears.
You can go to tirerack.com and read their reviews on various tires, but don’t believe everything you see. Each review is merely one man’s perceptions. I checked out Falken tires and saw a review indicating they were noisy. I bought them anyway and I am not getting any tire noise at all.
I agree with chaissos that noise level is a personal thing. And it may even depend on the car as well as the tires. (And maybe on the wife.) Read the reviews anyway. Can’t hurt.
Some Cars Are Noisy.
I’ve seen some common complaints about noise from certain kinds of cars. Seems like many Honda owners who post here are willing to live with road noise, for instance. I can’t live with it.
I enjoy quiet cars. I find them to be less stressful and less tiring (and therefore safer) to drive. Also, I enjoy music and talk radio. I won’t buy a noisy car and use that as one item I look (listen) carefully at before purchasing a car.
There are some tires that are quieter than others (often without sacrificing traction, wear, ride, and handling that could help a bit.
Check with a high volume tire dealer or two and you could get some advice based on customer feedback.
CSA
Wagons and hatchbacks generally have higher road noise levels than sedans, just because of the cavern in back. The single most important origin of that noise is generally the tires.
Tirerack and 1010tires both have good consumer review/feedback sections that rate road noise as one of the metrics. Check out their websites. You’ll be able to select some quieter tires and that should make a substantial difference.
You could also gut the car and install structural damping and matting like I did, but if you were so inclined you probably wouldn’t have bothered posting. It is a solution, but you have to be so inclined.
The shorter the sidewall , the stiffer the side wall. More noise transmission possible sure, but a pretty expensive experiment to see what the 16s will do.
In the case of 225/45r17, you’d choose a 215/55r16 to retain the same overall diameter.
Keep in mind all the other variables that make a difference but you’ll never know the results until after they’re mounted and driven on.
Continental is the cheaper line of General Tire so we must also wonder if that variable ( going to a better brand tire ) is an actual difference as well.
The problem with noisy tires is that it is hard to sort out if it’s just the tires or an interaction between the tire and the pavement - and the latter can be quite different depending on the paving materials used.
Consulting with Tire Rack is good from the average perspective, but noise can vary so widely that I think it is best to consult with a local tire dealer to see what works in your area.
And while I said 16s might be quieter, if it was me I’d just try and find a quiet replacement for my current 17s.
I feel the biggest factor in tire noise is the tread design. Softer rubber is a factor too. I don’t feel the cost of switching the entire set of wheels from 17 to 16" will make much difference.
Shop tires and look for a tread that is less “aggressive”. The larger the gaps the more likely you’ll get more noise. The opposite of a snow or winter tread is what you should look for. A dedicated summer tire would give less noise, in general, than an all season tire.
To get reduced noise you might get less traction in rain and snow. If you live in “winter” weather area you’ll have to decide what is more important, road noise or bad weather traction. Sometimes you just can’t get all you want in one tire.
Uncle Turbo, That’s What I Was Thinking The Last Time I Shopped For Quiet Tires For The Bonneville.
I thought I would need a less aggressive tread with smaller gaps, etcetera. I was wrong, though. I bought some Uniroyals that have a more aggressive tread than I had. They’ve got wider gaps and really work great in our nasty winter weather, but they’re nice and quiet. They have a long wear rating, too. When I couldn’t decide what to buy, I bought them on recommendation from a guy at the tire store.
I wonder if today’s technology used in designing, testing and manufacturing tires makes it possible to have good traction, long wear, good ride & handling, and still run quietly ?
I do know when selecting tires that the ratings are both helpful and tricky and a good wet traction rating doesn’t mean that dry traction is good or that the tire’s good in snow. Also, one cannot compare a wear rating from one manufacturer to that of another, but rather only within that brand. So, I guess knowing somebody who knows tires or gets feedback by selling them, helps.
CSA
Research or call tirerack.com and ask.
I have the same size tire on my wife’s Subaru wagon and they were relatively quiet in the factory Bridgestone Re92a(would not recommend tire though). The replacement Nokian WR G2’s were also very quiet tire which is a tire I would highly recommend if you encounter winter conditions(snow/ice).
The problem is not the tire size but the tires installed or odd wear patterns. Also be very wary of inexpensive tires. They may be silent at first and make you a happy buyer. However over their extended life 10k-15+ the honeymoon is long over and they turn very noisy. That has been my experience with Sumitomo and Falken tires which bother btw recommended by Consumer Reports.
Find a Jetta-specific forum, such as http://jettajunkie.com/cmps_index.php
It doesn’t matter what peole with other makes of cars say about tires on their cars. You need actual Jetta owners’ input.