While rim size matters, I think speed and driving habits have a bigger impact.

My NX wears 20" shoes for summer

 

Tire Size. Larger tires decrease your fuel economy because they are heavier, while smaller tires increase fuel efficiency. Bigger tires also have a higher rolling resistance than smaller tires which means they require more resistance and effort to get them rolling. U,S, Dept. of Energy

But--apparently if you do a lot of highway driving larger tires can be a mpg advantage. Other variables matter too, e.g. how you drive; what PSI you have in them, etc. All these can make it a close call re: mpg with slight edge to smaller. Smaller tires would usually give a better ride as well.

 

@LStoneX I’ve been super light on the pedal since I got my 350h and try use the pulse and glide technique whenever I can. Do you noticed a difference between your winter and summer tires? I know cold weather is not good for mpg so it’s a difficult comparison

@romer that’s some good info. Thank you for that. I have noticed that I’ve been getting better mpg when I’m on the highway which seems to be the opposite of the EPA says (higher in city/ lower on highway). On the highway my mpg is usually in the 40s

 

There's marked differences in my summer and winter consumption.

If I recall correctly, in the winter, my tank would get me about 650km on every fill up. But I think the engine wasn't fully broken in yet.

I'll wait to see what happens this coming winter and compare. I expect it would drop from the current 900km a tank, but perhaps it'll be closer to 700km than 600km on each tank.

 

I have the 20s and also see on average 35mpg in mixed driving

 

We've had the car not quite a month now and we just filled it for the first time. Fuel came out to be about 34 MPG. This is probably 80% short local trips on city streets and maybe 20% on the freeway. Also it has been hot here lately so AC has been on all the time.