if the same wheel and tire....normal widths.....some1 told me that the 16 is quicker....i have no idea how?

 

all depends on the outer most diamater of the tire...a smaller diameter is like shortening gears...larger is like longer gears..put 13 inch rims up front for a few minutes like a ricer on the street...then put your 16s or whatever on..youll get the point

 

lets go with a tire width of 205
205/50/15
overall tire diameter is 23.1'' and it will take 874 revolutions to travel one mile

205/45/16
overall diameter is 23.3'' and it will take 867 revolutions to trave one mile.
So it looks as though there isn't very much of a difference at all.

 

Depends upon how one defines "quicker". If all other things like weight, distribution of mass and diameter were equal, then the only thing "quicker" about the 16" combo might be steering response, due to the lower aspect ratio (45 vs 50 for the same width tire).

If the 16" combo were lighter and all other aspects were equal, then it would be "quicker" in several ways. Quicker acceleration, due to less mass having to be rotated, and less total weight of the vehicle having to be accelerated. Quicker steering response due to less mass having to be rotated around the steering axis at each hub assembly. Quicker suspension reaction to bumps and dips due to less mass having to be accelerated or decelerated in the vertical plane.

And of course as stated, if the 16" combo had a smaller overall diameter, and all other considerations were equal, then "quicker" acceleration due to a higher overall final drive ratio change.

And unless there's a sizable difference in any of these considerations, any differences in how "quick" the combos would be might well be unnoticeable.

 

I think the 15's but it will not be a big difference.