Here are a couple of links to the TireRack with some very good information on tire size vs. wheel size and more. I have seen a lot of conflicting information regarding what tire sizes you can mount on a specific wheel width - hopefully this will provide some insight.

Tire specs
tire tech

Here are a couple formulas for figuring out offset and backspacing.

Let's use the SVT Contour wheel for example.
We know that the wheel is 6.5 inches wide. So we start by dividing that number in half to get to the center of the wheel, and then adding a half-inch to accomodate for wheel lip. We've now got a total of 3.75 inches. Knowing that the backspacing on this wheel is 5.69 inches, we can get an easy approximation using this formula:

5.69 (backspacing) - 3.75 = 1.94
1.94 x 25.4 (conversion to millimeters) = 49.276

So we know that the approximate offset on this wheel is 49mm millimeters.


To calculate backspacing you use this formula:

(rim width ) / 2 + 0.5 + (offset /25.4) = backspacking

So for a SVT Contour Wheel:
6.5/ 2 + 0.5 + (49.276/ 25.4) = 5.69"

-Mark

Here are some good tire choices:

For all-season use (not much snow), and good treadwear, the Falken Ziex ZE512 is a favorite. It's probably the stickiest, best-handling all-season out there, and it's very cheap.

For a summer tire, you have a lot of choices. One of the best tires out there is the Yokohama Advan Neova AD07. It's super-grippy, rides well, handles rain well, but costs a pretty penny. Another great all-around tire that's sickeningly fast is the Kuhmo MX. Good treadwear for such a sticky tire, and pretty inexpensive. The Falken Azenis 615 is an autocross tire with super-stiff sidewalls that's probably overkill if you don't have a very stiff suspension. Still a great tire, but it's not quite as good an all-around street tire as the Kuhmo and Yokohama. The Hankook Ventus Z212 is another tire in the same Max Performance class, but it's pretty soft, and the Kuhmo will probably give you many more miles for the same money.

For a less-expensive tire, the Kuhmo ASX, the Fuzion ZRi, the Yokohama AVS ES100, the Avon Tech M500, and a couple other tires offer a lot of stick for not much money. I had the Fuzions and was pretty happy - very cheap, and quite sticky. I think the AVS ES100 is a better overall tire in terms of street manners. The Kuhmo and Avon are probably similar, but I've never driven them.

For street tires that are better in the rain than the sticky autocross type tires listed above (Azenis/Z212/MX), you can go to the AD07 or it's kin. Tires more like the AD07 include the Goodyear GS-D3, BF Goodrich KDW2, Toyo T1R, and Bridgestone S03 and RE050. But, the Yoko is much grippier all around than the others, and really in a class by itself. Now, however, there is another tire that's very similar: the Bridgestone RE01R. It's expensive, like the Yoko, but offers massive levels of wet and dry grip, while maintaining a level of street manners above the Azenis/Z212/MX.

New summary:

What summer tires should I get for my Contour?

Falken Ziex ZE 512 - Cheap, but very grippy in wet and dry for the money.

Falken Azenis 615 - A bit pricey, but great for autocross. Stiff sidewall, very grippy, not so good on the street.

Kumo MX - More streetable than the Azenis. Possibly the best dry grip/$ out there. $95 shipped from tirerack in 225/50R16.

Hankook Z212 - Worse treadwear but better wet grip than the MX, for the same price at DTD.

Or one of the expensive tires like the KDW2, GS-D3, AD07, RE010R, S03, T1R, etc.

ERROR: I meant Kumho SPT, not ASX, in the post above. The ASX is more like the ZE512, and seems to be a decent tire, but it's not at all in the class with the other summer-only econo-stickies.

Originally posted by Auto-X Fil:

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Falken Azenis 615 - A bit pricey, but great for autocross. Stiff sidewall, very grippy, not so good on the street.

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if you look around you can get the 615 for around 100-120 per tire