[JimJohnson]

On motorized vehicle races, I find my spot and lock my focus at a specific point and I use the K-3's DOF preview to know how much wiggle room I will have. Now about 'locking focus', first if I am using a zoom, it is preset and left alone. Many lens will shift focus during zoom changes. If I will hold my camera in position and wait for the subject to enter my preselected spot, I will use single rather than continuous AF and the AF lock button - that allows metering to continuously track things like moving shadows from clouds. Otherwise, I use whatever tool seems best to determine optimum focus and switch to MF leaving the lens focus alone.

The lower the cross-frame movement rate of the vehicle, the higher my keeper rate. Never a need to pan if the vehicle is coming directly at you or away from you. Having said that, the most spectacular photos have a sense of speed shown by blur, and that means cross-frame movement. So find the happy balance between your camera and body movement.

As previously stated, manual exposure means less delay in shutter activation. But might mean more post-processing. Using shutter priority exposure also means you have to develop a sense of delay prediction and fire before the subject hits your spot.