My first reaction was that the front motorcycle looked too sharp, didn't have enough motion blur.
Watched it a few more times and I wasn't sure anymore, but the first impression is probably the most important - especially considering how short the clip is.
(EDIT: On the other hand, when you step through it frame by frame, you do see a good amount of motion blur. The second motorcycle does seem to have more, though, so maybe it's the slight difference between the two that I was picking up on.)
(EDIT AGAIN: Okay, you know what it is? The first motorcycle is red, so it draws the eye more than the second and the viewer is more sensitive to any deficiencies in the image. The second motorcycle, being gray, is seen more peripherally so it comes across as more convincing. To my eye, it seems the red motorcycle could use more blur - or less red.)