I have extended studs in the rear
Will I be able to put a 20mm slip on spacer in the rear and still have enough thread for the lug nuts?
Or is 15mm the maximum? (I know 15mm slip ons work as I have a friend who's running this set up)

 

Measure the studs.

 

That would be too difficult, one must own some kind of measuring device, and thats not a yes/no answer dude

 

Oh since I don't really know how long I'd need for securing the lug nuts
I searched online and some say 6 turns? Some say around 1 cm of thread for the nuts to be secured?

I'm just really confused

 

6 full turns or aka 5mm spacer on stock length studs. I have a feeling 15mm spacers are it for you. But I cant say for sure, as ive never run extended studs and I dont know if they come in any different lengths. I thought 10mm over stock length was typical?

 

It is impossible for us to answer since we don't know the length of your studs. I am sure there is a length that they come in where it is possible but there can also be a length where it would not work. So yeah measure your studs.

 

I don't think you are going to be able to use the OE lugs with a 15mm spacer.