Will 21's fit on a GS? Or will you have to do modifications on the fender and so on ?

 

There is an 06 on here with 22s. Not sure what modifications were needed but it seems the 3rd gen GS accepts 22s better than the 2nd gen. But with that said it looks best with 20s.

 

With the new 21" tires on the market, 21s are a relatively easy fit on any version of the GS.

255/30-21 + 295/25-21 are about the same overall diameter as my current 255/35-20 + 285/30-20 set-up. I think 21s would look good on the GS- they would probably be at my threshold of pain in terms of what visually looks good (I personally think 22s look out-of-proportion on the GS).

Zone has a new forged one-piece wheel on the market. I might put a set on my 2GS just to see what they look like.

BTW, 21" tires that are available (255/30-21 + 295/25-21): Toyo T1-R, Pirelli NERO, MIchelin Pilot Sport PS2.
Falken FK-452 + Yokohama Advan Sport are coming in 2006.