im looking too buy new wheels and tires for my 2002 wrx, i wanna go with an 18*7.5, now i know typically when u increase the wheel size you decrease the sidewall, so stock is a 55 profile, so i would assume that in order not to mess up the speedo i would go to a 35 profile, but ive had a few company's tell me i would go with a 40 profile....now correct me if im wrong but wouldnt that screw up my speedo? and if so is there a way to recailbrate it?

You can recallibrate a speedo, but for the difference you're talking, it's not worth it.
The reason they're telling you to go with a higher sidewall is shock dissepation, the lower the sidewall the more chance of damaging the rim on uneven road surfaces.
Keep in mind, the larger the rim diameter, the more expensive tires become, you could probably get sufficient performance out of a 17" rim.

thanks for the info and advice

Yeah, living in New York I would go with a smaller wheel and a taller sidewall. I live in Syracuse and I wouldn't go above 17" because of the pot-holes. I have got to take some of the ones in front of my house: I am not exagerating when I say these look like something you'd see on the Rally of Cyprus.

Yeah, living in New York I would go with a smaller wheel and a taller sidewall. I live in Syracuse and I wouldn't go above 17" because of the pot-holes. I have got to take some of the ones in front of my house: I am not exagerating when I say these look like something you'd see on the Rally of Cyprus.

Agreed, IMHO, the only good reason to go to an 18" wheel is because you have a brake kit that won't fit inside a 17" wheel. On the size of sidewall you're looking at running, you're going to get to know all the options for fixing bent wheels.