The minimum recommended rim width for most 225/40/18 tires is 7.5", so some tire shops won't mount them on your 7" wide stock wheels due to liability... but yes, they will fit and work just fine without rubbing.
The minimum recommended rim width for most 225/40/18 tires is 7.5", so some tire shops won't mount them on your 7" wide stock wheels due to liability... but yes, they will fit and work just fine without rubbing.
^ For the first gen MS3 (which the OP has) they are 18x7"... the second gen MS3 uses 18x7.5" but that's not really relevant here. And I didn't say it wouldn't work, you can fit a 245 on a 6.5" wheel and ride on it. I said it wasn't recommended.
Where are you getting your specs? Because you should stop trusting them. I have personally confirmed the first gen wheels are 18x7J, and every automotive website I've checked confirms this...
EDIT: here's one of the first matches on google for ya... read the specs on the right. They are the same as those in the owner's manual, too, FWIW.
http://www.insideline.com/mazda/maz...7-mazdaspeed-3-by-mazdaspeed-accessories.html