I've been told that the extra 20mm around on all four tires in friction and additional air pressure, can make a bit of a difference (not specifying what that 'difference' is), especially since the added weight is applied directly to the wheels - not like additional cargo. Also, since the circumference of the wheel is changed, there is an effect on the effective gear ratio of the car – in this case the smaller circumference raises the effective gear ratio, putting me at a higher RPM at the same mph while cruising over the stock tire – this is also where I could have lost some fuel efficiency.
I don't see any flaw in the assessment except for the fact that....
1) the extra 20mm added to the tire is to its width, not its diameter and
2)the 245/50/16 is nearly identical in said over all diameter to the stock 225/55/16's. If you want to be specific, they're actually within 1.5mm of one and other in diameter. Really a moot point.
I was getting consistent gas mileage of about 25/26mpg for all the years doing the same exact driving route to and from college every week, and literally from the from the fill-up after putting the new tires on, I've never gotten over 22/23 - of course this is marginal and there are many other factors but I was getting a constant 25/26 and have never seen that ever again since the new tires – so I’m convinced there is some correlation... I'm very interested in seeing if this gets even a little bit reversed!
The difference in weight between the two tires is going to be ounces at best. That's simply not enough to account for a 3-4mpg mileage drop. And the added 20mm in width wouldn't create much additional rolling resistance either. If it cost you mileage in any way, its not an amount you would notice...I'm certain of it.
But either way, I just need someone to confirm if a 260/55/16 will mount to the rim and fit on the car.
Well, to my knowledge nobody makes a 260/55/16, but if one such size did exist, it would bulge slightly, but it would fit on a 7" wide rim.
But if anything, it’s going to worsen your fuel economy over what you have now, not improve it. Yes, you've increase the diameter (considerably...over 2.5") so highway cruising will drop your RPM. But the taller diameter and considerably increased rotational mass is going to require more horsepower to reach and maintain any particular speed level. The ability to increase horsepower means the need for more air and fuel will increase as well, thus decreasing your fuel economy.
Not to mention at 28.5" tall, it’s going to make your car look like a 4X4!!!
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