What does downforce upgrade actually do to your car?
Solution 1:
It would appear that down force helps long term acceleration and grip.
I performed a very unofficial test with 0 down force and 5 or 6 levels of down force. The outcome: with the upgrades my shadow I'm accelerating faster, compared to my shadow I was testing against. Also I finally managed to go up a certain hill, and that was all due to grip, not acceleration.
Other answers welcomed though.