How to improve your photo
I think if you zoomed in more and got less of the road in the foreground the riders would have been larger and the expression would have really been center stage of the shot. Any time you give that much space to something in the frame you're telling the viewer that it's important and here I don't think it is important, the face is what is the key, not the roadway.
One thing that helps when ever you are photographing more than one person is separation. If you had moved a bit to the left and crouched down the two riders would have had a bit of space between them. This would have also made them a bit larger in the frame. I know it's difficult trying to get that separation when things a zipping by, so it's important to see where the riders are taking the corner and plan accordingly.
You could have increased the exposure a bit just to brighten the face a bit, and you would not have made any other areas too bright by doing that. It's tricky when someone is wearing a helmet or hat to get good light on the face.
Shooting early in the morning or later in the day really adds to the quality of light and with that another whole dimension to the image. I realize that you're somewhat at the mercy of the race schedule, but that I's something to keep in the forefront of any photograph.