20 mph is the max speed of a bumble bee.
The average speed is 15 mph
I would say under 10 mph.
I don't know where the answer above came from, but I can tell you that I was just out riding my bike in no wind and had a bumble bee in FRONT of me for about 20 yards while I was going 27 mph. I would say they could go close to 30 for short distances in good conditions.