Just a day before this year’s “Great American Race,” on the very same oval of asphalt, a racing calamity that left at least 30 onlookers injured Saturday has changed the pace of the 2013 Daytona 500.

DAYTONA BEACH, Fla — Jimmie Johnson was simultaneously relieved and overwhelmed as he climbed out of his No. 84 Toyota at Daytona International Speedway on Sunday night. It was a different set of ...