Isn't a spoiler bad for performance on our Yari?

[cali yaris]

by speeding up air traveling beneath the car (smooth unbroken surface), it creates a small vacuum, which counts as downforce. So what you're saying is basically correct.

It would take a pretty high speed to be noticeable, I think.

[markitect]

Originally Posted by cali yaris

by speeding up air traveling beneath the car (smooth unbroken surface), it creates a small vacuum, which counts as downforce. So what you're saying is basically correct.

It would take a pretty high speed to be noticeable, I think.

This may start a huge argument, but I really don't think your underpanel will make any additional downforce vs stock. Yes the smooth surface will speed up airflow(dropping air pressure relative to the top of the car), but your ignoring the pressure drop created by the black "curb feeler" that is normally under the bumber (unless you can keep this installed and your pictures don't have one because your lowered).

If you think about an airplane wing the front has a big hump on top to speed up the air flow. The curb feeler acts(to some degree) like this hump
but on the bottom and therefore reduces lift generated by the general car shape. The question is which speed up the air more, the curb feeler, or the smooth surface. Anyone got a wind tunnel?

Still I think the underpanel is a great piece and will cut the drag a lot.

And I doubt the downforce difference matters at the yaris's speed limiter.