At 19 YO I had 50% on a windshield of an 88 Fiero GT and 20 on sides, at night sometimes I had to roll the window down to see pedestrians on the street trying to cross. Never did that again mainly because Westerville threw my ass in court after the 3rd ticket and sent a bailiff out to inspect my car that the TINT WAS REMOVED.
I stand corrected, I was always told and read that factory glass was a low percentage. Way lower than 28%.