The D435 camera will likely be the best fit for a project involving motorbike tracking, as the camera was designed with drones and autonomous vehicles in mind and has a new vision chip for advanced, rapid depth data processing capabilities. the D435 also has a wide field of view (FOV). It also has a larger sensing range than previous RealSense cameras.
You may also be interested in a 3D-printable project for R200-based Aero drones that enables a camera to be mounted facing down towards the ground.
What kind of range from the object are we talking about here?
The R200 based cameras such as SR300 and ZR300 work for medium range, and it sounds like you're talking about 15+ meters away.
In that case, you might be better off with object detection for a monocular (fisheye or RGB) camera.
And in that case, it's a matter of how well the object stands out from the environment you are filming it in.
Hope that helps,
Intel Euclid Development Team