Help with rear derailleur.
Hey guys, I have a Trek 1.1, it has the lowest line Shimano components. I would like to replace the rear derailleur to the Shimano 105, but when I look at different web sites there is several different 105 models. I'm kinda confused on which to get. Second question, if I change out the rear der to the 105, will I have to change the shifter to the 105 shifter also? Third question, am I better if just buying all new 105 components for the entire bike? Of course if it's not to expensive. Please share any helpful info.
And the rear cog has 8 different sprockets. So I'm assuming that means it's a 8 speed bike. Thanks for any help!