alignment problem with cassette and derailleur
 

I noticed that my rear derailleur fully extended does not reach the largest cog on my cassette. I was wondering what the problem is and how i can. Do i need a spacer to put on the splines of the hub? If so i dont believe the cassette i bought came with it. I am running sram on my road bike.

Low limit screw needs to be adjusted to allow derailleur travel further inboard. Assuming it's not a cable tension problem.

http://www.parktool.com/repair/readhowto.asp?id=64

thanks, it was a cable tension problem