Rob Kardashian's mission to bail out Blac Chyna cost him dearly -- TWO huge speeding tickets, one of which could cost him his license ... that is, if he had one.

Rob told us on Monday he'd lost his driver's license, and hinted it had something to do with outstanding tickets. That's not exactly what happened. We've learned Rob's license expired on his birthday, March 17.

His bigger problem is speeding. You'll recall, when BC got arrested in Texas ... Rob hopped in his Bentley and blazed across the desert to rescue her. According to law enforcement sources, New Mexico cops nailed him on Jan. 30 when he was headed east. 

Then on Jan. 31 -- on his way home with Chyna -- CHiPs clocked Rob doing 107 mph in a 70 through Blythe, CA.

Rob's attorney was actually in court Tuesday, and entered a not guilty plea for that ticket. The expired license is just a trip to the DMV, but getting out of the 107 is gonna be tougher.