What is meant by chassis effect? Like ground effect, so Downforce perhaps? Also the complete list of car design points, or at least the affected attributes, are needed to see what's what. Also suppliers chosen is helpfull to remove guessing.
I have a 2.5% improvement in chassis acceleration (4 DPs). And as you can see, there are no improvements to the acceleration bonuses.
Additionally, I have more improvement in handling +3 more than I should have.
But that was a long time ago (2 days). It's a bug or poorly written code.
Never mind.