It may depend on your state laws. I do tinting on the side and have 20% but I have been busted a couple of times for the darkness. Most states have laws of 35% max. But the darker looks better. I have 5% on top of my stock on the rear doors and rear slider.
My wife's car (not a ford but a trailblazer SS) I have 5% all the way around looks awsome
