Do you know how much of a difference it is to ride with specific gear ratio (example 48/16) with 28" wheels and 26" wheels?
Yes. You can do the math on this: (chainring ÷ sprocket) × wheel size. With a wheel that has an outer diameter at the tire of 26", you'd get 78 gear inches. With a 28" wheel, it would be 84 gear inches, or about 7% higher.
On a multi-gear setup, I've found that a 7% step is just about the smallest step that's really noticeable.
A larger wheel (including the tire) just gives a higher effective gear ratio.vBicycle gear ratios are often specified in gear inches, which takes the diameter of the driving wheel into account.
Gear inches = diameter drive wheel (in inches) × size front sprocket / size rear sprocket
[Source: https://www.sheldonbrown.com/gain.html]. Use of inches is traditional, you could of course use metric units.
Obviously, you can calculate the sprocket ratios which give comparable gear inch values for each wheel size.
Also, you can directly calculate the difference in effective gearing by simply dividing one wheel diameter by another. Assuming wheel with tires have an actual diameter of 28" and 26", a 28" wheel gives 28/26 = 1.07 i.e. 7% higher gear ratio over a 26" wheel.
Choosing 26 and 28" wheel diameters for comparison is a little strange. A 559mm rim MTB wheel with a 2" tire would be about 26" in diameter. A 622mm MTB wheel with a 2.25" tire would be about 29".
Assuming you would use similar tire sizes on each size wheel, you can simply divide rim diameters. 622mm / 559mm = 1.11, i.e. the larger wheel gives about a 11% higher effective gear ratio.