Vehicle Combination Average Speed Average mpg Weightage (per wheel)
BMW 3 Series equipped with
Original Equipment (16") Stock 38.7 22.8 42.5 pound (Baseline)
BMW 3 Series equipped with
Plus One (17") Lightweight 39.0 21.5 38.5 pound (-3pound)
BMW 3 Series equipped with
Plus One (17") Heavyweight 38.8 21.1 48.5 pound (+7pound)
Source :
https://www.tirerack.com/wheels/tech/techpage.jsp?techid=1081) Lightweight VS Heavyweight (10pound difference), additional 1.9% fuel economy, 1.7% in metric,
If a new set of wheels cost RM1700, you will need to spend RM100,000 in fuel to return investment, that will translate to 409,090KM odormeter at RM2.20/L/9KM, driving 225KM for 365days for 5 years to return investment
2) Noticed the OE Stock VS Lightweight Bigger tyres, although 1inch bigger and 3 pounds lighter, the fuel economy dropped 6-5.7%, from here I can conclude that the tyre low rolling resistance played a bigger role than just SIZE and WEIGHT.
Researched Concluded,
Hope that this could help wannabees like me don't be an idiot.

U can give it a try as an enhancement to the car, but don't hope too much to gain any savings from there
About tire is give and take... low resistance tire often don't give good grip while higher resistance tire is the other way round... so in the end of the day it still boils down to what u want to achieve, no right or wrong thou... some people just love to see their car got more economical than before even the money spent is not justifiable... but hey, its good for the environment atleast