Increased wheel diameter or body kit?

I have noticed that on quite a few nice skylines that I have seen that the gap between the wheel arch and the actual wheel is almost a perfect fit, on mine which is standard (R33 GTS-25T) that there is about a 10cm gap all around.

Is this due to people using a larger sized wheel diameter or is it due to a body kit?

I know lowering it will make it appear to reduce this gap but it wont be consistant around the wheel.

A 17 inch wheel has the same rolling diameter as a 16 inch, just more wheel and a lower profile tyre.Same with 18's not sure about 19's or 20's though, now that would fill your gaurds up.

Lowering the car man.

17s will make it LOOK fuller as well, more wheel, shorter tyre.

17s + proper lowering = better handling.

I already have 18 inch Momo's on it, with 235/18/40 tyres but there is still a consistant gap between the tyre and the guard. Lowering it will only decrease this gap at the top of the wheel arch so I'm unsure about how other cars seem to have only a 2-3 cm gap consistant around the entire wheel arch.

Body kits look great but with a full gtr front air dam and 16 225\50 tyres the car is just about undriveable the ground clearance is an absolute joke about 9 cm just getting out of my driveway was a nightmare.I mean really you see it all the time cant go over speed bumps unless you go on an angle and really slow . I got new tyres 235\55s all round and that raised the front by 14.5 mm and now you can drive it without worrying about every single tiny dip in the road so be very carefull about lowering the car because you actually have to drive it to enjoy it.