I have a 95 civic. and when i have everything stock, i can go probably 300 miles with a full tank of gas. but now i have CAI, Muffler, and 17 " rims, my mileage has gone down to 200 miles for a tank of gas... is it the big, heavy rims that are causeing the mileage to decrese or is it because of the diameter of the rims is different, so the meter is reading wrong?

its a combination of both the rim's diameter and weight