rubez

I am trying to set up my rear gears.

I have tightened the cable into the derailleur - but I can't select the biggest cog or the smallest cog on the rear cassette... I can select everything inbetween.

I think my chain may be the wrong length, as I changed from a 6-speed to a 7-speed cassette, and also changed my derailleur from a Tourney to an Alivio.

Does the chain length have any bearing on this?

Or does it sound like another problem?

Thanks.

Doc V

Could be the high and low limit screws are set such that they do not allow the rear derailleur to shift to those gears. It could also be that they chain is too short, but I would expect that it could shift to the smallest cog in rear cassette when on the small chainring since in the position there is still slack in the chain.

To check your chain length, follow the guide at Sheldon Brown's website Derailer Adjustment.

Carbonfiberboy 

What are you shifting with? Downtube? Bar end? Brifter? I suspect a mismatch between shifter/derailleur/cassette. Maybe the limit screws, but that seems unlikely. It's not the chain, though follow the advice to get correct chain length. Too short a chain will sooner or later put the derailleur into your spokes.