Remember Chris Johnson's EPIC 4.24 40-yard dash at the 2008 NFL Combine???
Yeah, CJ2K tells TMZ Sports he coulda ran it in UNDER 4 seconds!!!
Chris says he came into the annual pre-draft event weighing around 200 pounds ... but says if he had shed 30 or so lbs for the drills -- he would've gotten into the 3s zone on that historic day!!!
"I think [I could have run it]. If I would have went to the combine at 165 ..."
So, why didn't the former NFL superstar do it!