First and forth test both use 1random brickpack ramp bricks, the ramp bricks in that pack are known to have non-properly working collision. This renders those tests inaccurate. I would suggest redoing them with default bricks.
Really? That's interesting. And you do have a good point.
To be fair, the fourth test wouldn't work without the ramp brickpack that I used. Given that the default ramps are far to steep for anything outside of a freestyle buggy to climb.
And the bricks used on the first test really suit the first test quite well. I'm not sure a default brick would suit the test as well.
Couple that with the fact that I don't think that there are any default bricks that are set to the same angle and degree (and size). You could also look at it this way: if they can climb those bricks with non-properly working collision. Then they (the cars) should easily be able to climb default bricks.