I was wondering if there is a diffrence between a 17 in. rim and a 18in. rim performance wise? If you have any info on the subject that would be great!

 

Technically speaking, if we consider the exact same style rim (with only the size difference), the larger rims will tend to perform worse (in acceleration). It has to do with momentum and rotational mass. Most people with the large rims get them because it makes the car look better (in my opinion).

There are also a few other factors to consider. For a larger rim, you tend to get rubber that has a lower profile side wall which helps performance in terms of handling. A lower profile side wall usually means it is stiffer and there is less roll onto the side wall in hard cornering. But, on the other hand, you can also buy a smaller rim with lower profile tires. This will give you pretty much the same handling benefits. If you take this option, you have to consider that a smaller overall wheel size will affect your odometer/speed guage, and also your car will be lower.

Personally, I would go with either 15" or 16" rims with some low profile tires.

 

on this site www.oktire.com they say its about 22-24 inches in diameter for stock civic tires including rim. Now if you were to put some 17" rims on then the tires would need to be 45mm (205/45/17)
in thickness to be equal to the diameter you had before so you're speed gauge will still be accurate.

For those who don't know what these numbers mean:
205 is the width. Depending on the wheels you are getting the width might vary and has increments of 5. I'm not sure but I'm guessing that its in milimeters.

45 is the thickness or height of the tire. This is around the thickness you want for civics if you are buying 17" wheels.

17 is the wheels since in inches.

I could be wrong so if anybody sees a mistake in this please correct me because I learned this on my own when I was looking for some performance tires.

 

you are pretty much right. Just to confirm, 205 is the width of the tire in mm. but the 45 does not refer to the height of the rubber in mm. This is the PERCENTAGE of the width of the tire. For my stock SiR, I have 195/55 15's so the overall diameter of my tire is calculated as follows

195mm x 55% = 17.25mm = 4.22 inches
diameter of rim = 15"
Total wheel size = 15" + 4.22" + 4.22" = 23.44"

So, for a 205/45 17

205mm x 45% = 92.25mm = 3.63
diameter of rim = 17"
total wheel size = 17 + 3.63 + 3.63 = 24.26"

So for my SiR, these tires would be too big. I am currently running 17's and the rubber is 205/40 17

for an overall wheel size of 23.46"

 

thank you for that info, that will surely help me in the future, Dave