Glacialone

ronsal

If after reading all of the above postings, which are saying go w/dedicated winter wheels/tires, which I also pretty much agree with, I would suggest looking at TireRack. They have wheel/tire packages for 18, 19 & 20's. If you plug in your vehicle, what comes up is all stuff dedicated to the SQ5 - anything will fit that is on those pages. The 19" selection seems to be the largest, and you can go from 1200 and up for a complete package.

Good luck whatever you do.......

SLLAuWo

Your SQ5's summer tires should not be driven below 7 C (45 F).

For best traction and safety in snow, consider 18" or 19" winter tires and wheels. The smaller the wheel and the narrower tire, the better.

Tire Rack is a good source of information.

Glacialone

Solid advice.
The following is meant only to nuance the underlined part of this advice as it is really only true in deep snow - which most urban drivers do not encounter very often - and really it is the width of the tire patch, not the diameter of the wheel that aids in deep snow traction. The offset is that you lose some traction on plowed and icy surfaces.

I've never read anything convincing that explains why a smaller diameter wheel is truly better in snow, other than that smaller wheels are typically (although not always) narrower.

FWIW, we went with 235/60/18s on my wife's Q5. The OEM wheels take 235/55/19 tires - there is no way I would go to 195s or 205s to get any appreciable and occasional deep snow advantage as a trade-off for losing 10-15% of the tires' contact patch for when the roads are bare or icy which must be about 95% of the winter in these parts.

Benzie

I'm not sure that the smaller diameter of the wheel offers any advantage in terms of out right performance either in deep snow or on ice, with regard to the contact patch. What the smaller diameter wheel does do for you is offer more options for different snow tires, since snow tires are more commonly made for smaller diameter wheels - you will find more snow tires for 17, 18 and 19 inch wheels than you will find for 20 and 21 inch while keeping the revs per mile (outside diameter of tire) the same. Also, taller sidewalls help with the generally rougher terrain of winter roads in terms of absorbing potholes and other road imperfections which are more common on winter roads and less easily avoided while driving.

Glacialone

I agree - there's zero advantage to the taller sidewall you get with a smaller wheel other than (as you suggest) a bigger selection of tires, lower price, and (arguably) more cushioning for potholes and the like. Cost and selection were the only reason why I went with 18" for the winter tires/wheels on the Q5 (vs the stock 19s).

andrewmr

Smaller wheels, while keeping the same overall diameter, will offer more sidewall compliance.

Benzie

Yeah, well a couple of things I find that car owners don't always appricate when it comes to fitting different tires/wheels. 1) The importance (for speedo/odo accuracy and correct operation of the tranny) of maintaining the factory original rolling circumference even while changing rim diameter and 2) the huge difference in ride quality even just one inch in rim size can make since tire sidewalls are a primary suspension component. My summer wheels have 20 inch rims and my winters have 18's. Let me tell you, replacing 2" of aluminum with rubber sidewall makes a night and day difference in ride quality - my winter wheels ride like pillows in comparison. Now of course there are other variables like tire pressure and rubber compound that come into play, but all things being equal with tire pressures adjusted correctly according to load and load rating of the tire, it is not debatable that one will give a more plush ride and more protection for your suspension and rims from potholes. Also not debatable is that the handling and quickness of steering will suffer with taller sidewalls since handling is the main reason for low profile tires in the first place (well that and fashion for some) and at the same time the reason they're not needed or even practical on winter roads in inclament weather.

SLLAuWo

Well said.

Glacialone

I agree. In my household, we've gone only 1" down for winter wheels for each of our rides - my wife's Q5 and my CTS and I notice a slightly more compliant ride but a huge difference in road feel. 2" of sidewall would be very noticeable.