Sheriff’s officials said the man, a regular bicyclist, suffered to badly broken ankles but did not appear to suffer life-threatening injuries.
The crash occurred shortly before 9 a.m. on Lemon Avenue near Valley Boulevard, near the Walnut border.
“He’s going to be fine,” one sheriff’s deputy said.
The big rig was determined to be at fault, but the driver was not cited or arrested in what officials believed was simply an unfortunate accident.
The elderly man was flown by helicopter to Los Angeles County-USC Medical Center for treatment.