Would not tighten at all in the car. Best way I can describe is imagine a zip line that's 5 ft long, and you string along a 3 ft "car seat." The other 2 ft of slack allow the car seat to move from side to side. That is what occurred with both this seat as well as the DLX. No matter how tight I had it installed, it still slipped from side to side. It also lifted on the back end that was closest to the front seat where adults sits. Meaning, if I were to accelerate rapidly (unrealistically, but not so much if I were rear ended at high speeds), the seat would lift off at it's rear and the child's face would launch towards the actual vehicle seat. I know this is hard to describe via text and not seeing it, but hopefully this makes sense. Very disappointed, as we totaled our car years ago and our daughter walked away with a minor abrasion because of her amazing Graco. Wish this would've worked.