Noob Question..
 

Ive ordered HSD coilovers, basically they make stance coilovers now my question is wdo I absolutely need cusco rear control arms?
Ive had a genesis coupe before on eibach lowering springs and didn't need to modify any other parts of my suspension?

I'm not really good with the suspension aspect.

You won't absolutely need them, some people's rear camber is "ok" after the drop. If you want to be able to adjust it you will need either the Whiteline camber bushings or somebody's LCA, doesn't have to be Cusco there are other options on the market.

I have 255/35/18 in rear and 225/40/18 in front.. Make a difference now?
Does it reduce the longetivity of the suspension?
what is the difference between the camber bushins and teh cusco rear control arms?

Tire size doesn't make any difference on the alignment unless it was something crazy.

The camber bushings are cheaper but more difficult to install and set up than the control arms. Whiteline has a control arm coming soon, Stance has some, I use SPC but there are others out too.

So technically whats the difference between the new ones and the stock ones? why must they be changed?

The only reasons people will change them is to take some of the neg. camber out of the rear or simply for the bling factor.

To elaborate on this after a mild spring drop my camber was a full degree different from left to right. I wanted to be able to adjust it and the stock suspension has no camber adjustment.

Alright makes sense. I'll look into it , after i've installed the coilovers..
I'm guessing I'll need an alignment after 100Km on the coilovers? or when i get the control arm?

Both, align it after install and if the camber is too bad off order a set of control arms.

Kk thanks