my state(co) says the law is 28 and I have 20 on 1 car and 5 on another and never been hasseled. Come to think of it I have never heard of anyone geting a ticket for it. anyway if you dont want to risk it do 35 on only the front 2 windows thats all the law covers and what ever on the rest,except windshield of course. and if u only want to press ur luck a little do like 30 up front and 25 on back. I would not make a huge difference between the front and back windows though cause if their dramatically different u can tell and it looks like shit.