The missing factor here is the appropriate definition and description of what you give up when you race; it's called "reasonable assumption of risk".
You should expect the car will go fast.
You do not expect that the track owner has forgotten to fill in the 20 × 20 hole in the shut-down area he dug up to repair the drains.
You expect the other driver may lose control.
You do not expect the other driver to be 10 years old or drunk.
You expect some mechanical part may fail.
You do not expect a spectator to cross the track near the traps.

See any difference?
You did not waive or forfeit your claim to damages for any of those examples, no matter what you signed.