Give me some of your hardest riddles? (with solutions in spoilers)

i help you stay grounded when speeds are high
though im not a bird i can still make you fly
im often found on the back not the front
what am i that gives your ride a cool stunt

What's in my pocket?

The poor have it

The rich need it

If you eat it, you will die

She comes sometimes at need,
But never at your heed.
To meet with her is jolly,
To push her would be folly.

Who is she?

edit: for bonus points, I first came across this with a second step in the puzzle. Not a riddle, but a different kind of puzzle. Solve this:

Though that's not the same text I had the first time (it was in a D&D game and the text was related to that), the same technique would need to be applied to read the above text. The riddle's solution is relevant.

Three women are sitting at a parlour eating iced cream.

One is Licking the cone.
One is sucking the cone.
One is biting the cone.

Which one is married?