wheel and tire are two seprate things. if your refering to tire size as stated in your question you cant increase diameter without increasing wheels size. if your talking about increasing wheels size then the only issues you will have with fuel mileage is if you dont properly match the tire. in the case of a 16" wheels its 215(or 205)/50 R16.
My car came with 15" wheels with 205/65R15 tires on 15X6 steel wheels with hub caps. I upgraded to 205/60R16 tires on 16X7 alloy wheels
Larger diameter and larger width typically means more weight, but alloy wheels weigh less than steel wheels for the same size wheel
- By keeping the tire diameter the same, I was able to maintain the speedometer accuracy.
- By keeping the tire width the same, I was able to avoid any additional weight/rolling resistance from a wider tread.
In the end, I was able to keep the weight of each tire/wheel the same. No effect on fuel economy. The car rides as about as smooth as it did before, but handles a bit sharper.
The alloy wheels I bought were fairly cheap (Fondmetal 6700) and not very light for the size. If I had bought more expensive alloy wheels that weighed less, each tire/wheel would have experienced a new weight reduction compared to stock.
For a given wheel, the weight will vary greatly by manufacturer/model.
Take a look at this link and you'll get an idea how much wheels weigh.
Wheel weight is definitely a factor in fuel economy, but tire selection plays a role as well. Even for a same size tire, some tires have less rolling resistance, while some may have a lot more.
When I had my Maxima, I used to have 205/65R15 92S Michelin XH4 tires. S-speed rated (112 MPH) long wearing tires with extremely hard compound. Grip left a lot to be desired, but I got over 70K miles from those tires. I switched to Falken ZE-327 V-rated tired (149 MPH rated) tires of the same size 205/65R15 92V. Much much better grip, but lost 1-2 MPG after I changed the tires. Lasted 40K Miles.