You can compare different wheel/tire sizes to each other with this link...Basically, if you keep the overall diameter of the the same, you should be in good shape (so long as you don't go crazy with the tire width.)

http://www.discounttire.com/dtcs/infoTireMath.dos

Tire manufacturers recommend certain width wheels for certain width tires, You should check the specific tire you are looking at for the recommended wheel widths (Minimum & Maximum) specified for that tire. You should stay within the recommendations of the manufacturer.

Now this doesn't mean that a 225 width tire won't mount on a stock 6.5" wide rim, it will, but you may be crowning the tread so they'll wear quickly.

FYI...stock width on the Mazda3 wheel is 17"x6.5, the wheels I have are 17x7 Mazda6's.

WIth a 60mm offset 17x7 wheel and a 225/45R17 tire, I rub a little at the front tires, toward the rear of the wheels at full steering lock. Nothing gets damaged with this rubbing and the only reason I noticed it was rubbing was when I was changing my tires the other day and saw the rub mark on the inner fender liner.

 

thats what im running on my car with no problems at all.

 

215/45R17 would work just fine. Your speedo would be off by ~1mph slow at 65. (Actual 98.2mph - when speedo reads 100 mph) Your new tires would be about 1/4" shorter than the 205/50R17 tires that came stock.

 

First of all, your logic is faulty. Just because it's an add-on does not mean is doesn't affect warranty. Any modification that affects a warranty issue can void a warranty. Secondly, are you saying there is no rear anti-sway bar on a stock Mazda3? Even my whimpy lil Hyundai Elantra came with anti-sway bars front and rear.

 

swaybars (anti-roll bars) come stock on the mazda 3, both front and rear.

 

I didn't want to say for sure because I haven't looked under a 3 before, but I would have been shocked if they didn't have sway bars.

 

Mazda3 is probably the best handling vehicle in it's segment. (0.87g on the skidpad stock....same as a Nissan 350Z)