Thank you for that info and yes the cars are going approximately 100 mph at the 60 foot mark. Would I be better off with less zoom (say 50mm) and a faster than 1/150? Should I let the camera select Aperture and ISO? I'm not confident enough to go all out manual. And I can't afford to miss shots. The cars are running 5 seconds and less in the 8th mile. So getting clean shots is a must.
Photography is an art form and technical at the same time. So there is no "one right answer" for a particular attempt.
A wider focal length would help with camera shake, but then the subject will be so far away that you lose that "intimacy" that you can have with a longer lens. I suspect that the longer lens is the one to use. 150-200mm seems about right to fill the frame and get the viewer "into the action". Just have to hold the camera steady (or invest in a really expensive lens). There some tricks to use: Get a monopod, and use it to help steady the camera. Use a fast shutter to "freeze" the motion. Learn to be selective in what shots to make and which ones to pass up, knowing in advance that they will be blurry. Blur on purpose (the opposite) to create "artful" images.
I would probably let the ISO go on "auto" because what the heck, it's just am image processor, and if the camera is allowed to go ahead and process the image you took, let it.
Aperture is another thing you should have completed control over. I would probably put my camera into "aperture" mode, and watch the shutter speed as I compensate for exposure while watching the meter in my viewfinder. The reason is because I want the aperture to set the DOF, so as long as I can still get my shutter speed fast enough to freeze the motion, then I'm good.
Try to minimize the "cross-frame" movement, so you want to be almost inline of the cars' movement, as at the finish line, for instance, so the relative motion is more toward you, and not completely sideways to the camera.
If the sideways shot is the only one you can get (or want) then learn to "pan" to keep the cars sharp while blurring the background.
Gotta go.