I like the low slung look. I don't want to go to an 18 in the rear because I want the bike to stay low.

If you have them can you please post a pic.

 

have a look at mine

 

Why would it not have the "low" look with the 18" rear? It's the diameter of the tire that determines that not the wheel. You just go with a thinner sidewall on the 18.

I've also noticed that a lot of guys run their factory 16" on the rear since it's hidden by the bags anyway.

 

Here ya go 21" front 16" factory on back.

 

Megalifted is correct. It's the outside diameter that's going to determine the bikes stance. Your stock 16" is within 3/8" of the 18"... So hard to visually see much difference. You can go either way. The ride on the 16", with it's more balloon effect, gives a little smoother ride than the 18". But many say the 21X18 combo is very comfortable, and provides a more sporty ride in comparison... Hope this helps.

 

The 21 in the front actually raises the profile of the bike. You need to lower the forks to get it back down. The 18 v/s 16 in the rear really isn't much difference in height.

 

All my dirt bikes have 18"/21" wheels. Never realized how cool they looked till now

 

I did the 21/18 and just lowered my bike. 1" in the front and I did the Prog. 440 (I think, it's been a while) in the back which are adjustable. It rides great.