This will come as completely new information.

There will be nay sayers about this, but then most do not both putting this into the mix.

When you are planning to photograph motion combined with the camera put into motion you truly need to take stock of two points. Please understand that as you view through the view finder of a camera you see a car drive from one side to the other side of your view finder. This is true for the observed motion, BUT your lens is delivering the image altered in three dimensions. The car you see driving from one side of the view finder is I fact being delivered to the film/sensor in the OPPSITE direction.

So if a car in your view finder drives from right to left in that view finder, that car that is captured by the lens and placed on your film/sensor is in fact moving in the opposite direction moving left to right).

Further, the focal plane shutter of your camera will also have an impact. Say your shutter moves from the right side of your camera to the left side. There will be an effect if the shutter is moving in the same direction that the image is being when inverted by the lens. This can elongate or compress the image die to the direction the shutter moves with regards to the physical motion of a pan.

Finally, bear in mind that your sync speed is the fastest speed allowed by the shutter. Increasing the shutter speed will only alter the timing of when the first and second shutter curtain are in motion. Twice the shutter speed above the sync speed will see the second curtain released after the first curtain has made half the passage and the shutter is 'painting' the image on the receptor part of the shutter time.

These factors will effect the outcome of an image.