SAN FRANCISCO (KPIX 5) – Three months after retiring, former “Late Show” host David Letterman was in San Francisco on Monday.

Sporting a thick beard, Letterman was in the Bay Area to celebrate the IndyCar Series championship, which took place Sunday at Sonoma Raceway. Letterman co-owns one of the racing teams.

“This has taken up a lot of interest and time and attention, and without it I don’t know what I would have been doing,” Letterman said.

Looking back at the season, Letterman said, “You start in Florida, you end in California, and to be in it at the end is all you want. As long as you got a shot, that’s all you want. It’s tremendous, it was very exciting.”

When asked if he plans to watch Stephen Colbert take over his spot next week, Letterman said he will be in the front row with his family.

The new “Late Show With Stephen Colbert” premieres on KPIX 5 on September 8th.