Bryan Cranston -- WITNESS in Jay Leno Bike Crash

"Breaking Bad" star Bryan Cranston was mere FEET from the motorcycle crash that nearly took out Jay Leno ... and tells TMZ he knows what REALLY caused the bikers to lose control and wipe out that day.

We broke the story ... a bike with two passengers slammed into another vehicle at the 2011 "Love Ride" ... coming thiiiiis close to taking out Leno.

Christina Silva -- the rider who captured the crash on camera -- says she was unfairly blamed for causing the crash ... and now Cranston seems to back her story.

Bryan tells us ... "I was about fifty yards behind in the same lane as the downed riders. It happened because of excess speed."

Cranston explains, "Guys were flying past me. When you put yourself in that position you are forced to make quick decisions when coming upon slower traffic. Not a good mix. Slow it down - enjoy the ride!"

As for Leno ... Bryan says he didn't just ride off into the sunset -- "Jay stopped to assist and went to the hospital with the injured riders."