if you look at the stock tires, the overall diameter of the 16, 17, 18 and 19 inch tires is all almost exactly identical.

 

I'm gonna change out my front wheel as well. You can't see the rear wheel with the bags & pipes in the way. As far as handling it should be fine. Swap both out if it bugs you, as for me I'm happy with just swapping the front out.

 

IF you do the front only and it bothers you that the back is stock...another option would be to get your stock back wheel chromed... (excgange..***** Shiney, etc.) it will cost probably half of the rear Agitator... and you really only see the lip of the rear wheel so if its chromed it might look like a better match.... AND if you don't like the chrome stocker i'm pretty sure you wouldn't have any trouble selling it to recoup a good portion of your money...
I'm kinda in the same boat as you but for a different reason....i'm NOT worried about the different size wheels (cuz like others said, by using the correct profile tire they all pretty much come out to same overall diameter)... I consider doing the 19" front Agitator only cuz i don't really want an 18" rear wheel.....

 

Just bought a 12 SG. One of the first things i did was put a 19" RCC contrast cut wheel on front. I chickened out on the 21 for fear it would change the handling..

The 19 looks nice.

Didnt change the rear since you dont see it anyway and it was black already.

Didnt seem to affect the handling at all.

 

I'm going to switch out my wheels also on my 12 SG. I was thinking about just doing the front, but if I switch both I can sell the tire and rims as a set. Makes selling easier and the money I get from the sell will help offset the overall cost. JMO though.

 

Thanks for all the replys,

On my black matte bike the stock rims are the black/aluminum contrast wheels so the Agitator black contrast rims should be a whole lot less noticeable for sure. Would like to do the klockwerks tire hugger rim like one of the guys on this forum used and if I can find out which style was used. Thanks again.

 

I run the 19" Agitator on the front with low profile Dunlap and an 18" Agitator in the rear with 180mm low profile Dunlap on my 2011. Seems to handle very well. I believe that I can go up to a 200mm in the rear without mods.