Mileage Difference??

Recently i have done some modifications in my 2006 swift..i have purchased new alloy wheels and tyres.. basically i have upgraded from 165/80/R14 to 215/55/R16 for giving a new look to my car..but i am worried about my mileage...i want to know what impact it will have on my mileage.. earlier my car use to cover 260km from 25 ltrs CNG..
I didn't find the right solution from the internet.
References:
https://www.carwale.com/forums/43404-mileage-difference.html
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