the professor

Is there any noticable difference looks wise between a 40 and 45 tire? Also is there any other pro's and con's between the two?

Im looking at either 205/40/17 or 205/45/17 Kumho ECSTA Supra 712's

wormburner

40 and 45 are not measurements in millimetres. They are percentages of the total width of the tire (contact patch.) If you have a 205mm width tire, then the profile (height) is 40/45 percent of that. 205/45/17 has a good chance of rubbing if your car is lowered in the least. The profile is just too high. It may also throw off your speedo slightly.

DumbasSi

The 40's will look a tiny bit lower, but the 45's will ride better. Try this link for sizing and stuff.
http://www.miata.net/garage/tirecalc.html

imported_f20accord

i say go with the 40 series

plus the 205/45 combo is a rare tire to come by from experience

Anthony

The 40 series tires will keep your overall diameter similar to stock. The 45's will be too tall on 205/17's.

CX99

40 series for sure don't get 45

imported_twinbros

If your car lowered? If so how much?

Most guys here will tell you to go with the 40 series tires.
My advice:
If you car is not lowered, go with the 45 series because the higher sidewalls will cushion your rims better (a must for fragile Taiwanese rims) The added bonus is the the wheel gap is less noticable.

If your car is lowered, ignore what I wrote on top because the TIRES WILL RUB your fenders.