18inch to 16inch

So... I'm trading my 2013 JSW TDI in for a 2015 GSW SEL TDI. The GSW has 18 inch stock wheels the JSW has 16inch. After doing a little research the tire selection for the 18inch wheel is not very promising for a good all season tire and the ones on my JSW are still in very good condition. I still have not turned in my 2013 JSW and it has 16inch wheels. I need to know if the JSW wheels would fit the GSW. I do know that I will have to get a hold of a VCD to change those values pertaining to tire size. Also by changing the tire size will it lower the overall car height, I am trying to keep as much ground clearance as possible?

Discount Tire said that there was no difference between the 16inch and 18inch as far as the wheel goes. I went by the VW service center and they concur and said that if you install a different size wheel the cars electronics will set the new wheel size change automatically.

Hard to believe no one in the forums knew this stuff, or would give an answer.

1. All mk5,6,&7 are 5x112 bolt pattern. All stock wheels will fit each other within these platforms. (Golf, Jetta, JSW, GSW...)

2. Usually tire sidewalk height gets taller/shorter with wheel diameter getting smaller/larger.
Stock sizes are something like 225/45R17, 225/40R18.
Here's a handy calculator to use that will tell you any measurements you might want to know. https://www.miata.net/garage/tirecalc.html

3. My stock wheels are 18x7.5 et51. Stock tires size is 225/40-18.
I have put about 10k miles on my current tires: Sentury 225/40R18 - 92W
UHP (Ultra High Performance), "Extra Load" rated, and All Weather (though it doesn't say "all season") and they have a 40k mile warranty.
Sticker price was $63 (I think) at Discount Tire. So far they handle great, car goes exactly where I want it to - wet or dry. I even drove around in that "ice storm" that shut down San Antonio TX a few weeks ago. No problems. Tread looks good and I rotate them every 5k miles.
(I ran Bridgestone Potenza RE760 Sports for 3 sets prior to these - no reason to go back, these are cheaper and every bit as good.)

People in this forum tend to not answer stuff if they feel it's been answered 5000 times before. Or they didn't see it. Or they figured someone else would answer. Or they saw it right when their wife yelled at them to get off their darned phone/tablet/computer.