Adam Rippon Goes Racing (at 150 MPH!) with Fellow 'DWTS' Champ Hélio Castroneves: 'My Heart Was in My Throat'

Adam Rippon has checked off a lot of firsts in the last year — winning his first Olympic medal (in figure skating) and then winning the Dancing with the Stars Mirrorball Trophy — and on Sunday he added another to the list.

While attending his first IndyCar race, in Toronto, he rode for two laps in fellow DWTS champ Hélio Castroneves‘ two-seater as part of “Honda’s Fastest Seat in Sports.” They got up to speeds of more than 150 mph.

“It was definitely the fastest I’ve ever driven in my entire life and my heart was in my throat the whole time,” Rippon, 30, tells PEOPLE.

“The hardest part of the entire day was sitting in the car waiting to start,” he says. “It was incredibly hot in there. I really don’t know how those drivers can do that for 85 laps. I was wiped out after two — and I was only the passenger.”

Like Rippon, Castroneves, 44, won DWTS (in season 5) and is an accomplished racer, with three wins at the Indianapolis 500.

Riding with him “gave me a whole new respect for these drivers and what they go through during a race,” Rippon says.

Catapulted to national fame in last year’s Winter Games, Rippon competed in DWTS after returning home (among other high-profile appearances, including a turn on Will & Grace).

This year he launched a YouTube channel and will release a memoir, Beautiful on the Outside, in the fall.

“I think [readers] will find a lot of humor in the way I grew up and in my family situations and different situations I got into and the characters and people I’ve had throughout my life,” Rippon told PEOPLE earlier this year of his book.

Of his “amazing” racing day with Castroneves, he says: “It’s always great to step out of your comfort zone and experience something new and this was definitely out of my comfort zone.”