The blurriness of the front of the car comes from the point you are picking on the car to pan around. Ideally you would be looking to pan around a specific point on the car as opposed to the actual car itself, I normally pick the front wheel nut and try to aim the camera at that. It makes it gives you a more accurate thing to track and should make the front end of the car sharper with the motion blur affecting the back of the car which is much more pleasing looking than the rear end sharp.
Not an R/C shot but the theory is exactly the same you can see were i've panned around the line of the front wheel and thats left a fairly small section sharp as it's been panned with an ultrawide angle.
