He does slow down quite a bit right before the finish line, so that is a good spot to overtake him if you are close behind him. Other than that, his speed doesn't really vary, ahead or behind.
Also, try not to let him step on you - when you are flattened, you lose a lot of valuable time.
There is also a shortcut of sorts that you can use - it is marked by a set of bushes. You can also recognize it ahead of time by the rock outcropping and a blue balloon nearby.
If you get the boost at the start, you'll be ahead of the Triceratops.
Also, if you are behind the Triceratops, homing missiles are a good way to get ahead of him.
Getting the blue balloons (if possible, some of them can be tricky) are your best bet to get ahead of him quickly, and to extend your lead once you have it.