I recently purchased a set of the SSR's for my GXP from TireRack.
As reported they are a tight fit in the hub area. A little grease helped mine slide right on no problem.
Any one that has these please check your valve stems (screw in type) mine were loose and leaked until they were tightened.
I like my SSR's... I sincerely believe that I can detect some positive difference in the handling and ride quality due to the reduced unsprung weight.
Rickey.