He'd heard about people who ascended too quickly and developed nitrogen bubbles in their blood. Leo wanted to avoid carbonated blood.

Never mind," Leo said. "I'm pretty sure pi is, uh, 3.1415 blah blah blah. The number goes on forever, but the sphere has only five rings, so that should be enough, if I'm right."
"And if you're not?" Frank asked.
"Well, then, Leo fall down, go boom. Let's find out!

I try not to think. It interferes with being nuts -Leo Valdez

Delaying death is one of my favorite hobbies

The way Leo figured it, he spent more time crashing than he did flying. If there was a rewards card for frequent crashers, he'd be, like, double platinum level.

You can keep watch, in case – you know, the lake decides to attack us or something." - Leo Valdez