yea your right factory tint is made in the glass

 

so you HAVE to tint over it if your tinting. is there any real math to tint? like if you put 10 over 20 does it make it like 5? lol or do you just have to measure it with a meter?

 

if you go to someone that knows what they're doing with experience they can pretty much tell you what will look best. if you want 5% i would prefer just to go with it on the front and have your tint guy match up the back, i'm pretty sure i had a buddy that got either 15 or 20 on his back windows of his Sierra and it matched up well. For you in the tahoe you probably want to do that so you can see out of it, or you could just roll down your windows like i do haha

 

what i have always done before is put 5% over the factory tint in the back, and on the front 2 windows i just put legal which is 35% here in texas, from being that the rear is so dark it makes the front ones look darker than 35%.... by the way I can still see out the rear windows at night while backing up...