How do you get panning shots sharp at an autocross?

The short answer is that 1/60th of a second is definitly too slow for capturing moving cars during an autocross. At the speeds those cars hit between cones, 1/60 is going to blur the subject, even if your panning feels smooth. To freeze motion and acheive that sharp subject you've seen in event photos, you need to jump significantly higher. Aim for at least 1/250th or even 1/500th depending on the car's velocity and the distance you're from it. If you are using a cheap zoom, tracking the focus with continuous autofocus will be a pain, but manually focusing on the driver's face or the car's main mass is often much more reliable while you are panning. Even if the wheels become a blur, the sharp body of the car is what you want for those dramatic action shots. The lens quality also matters a bit, but often the shutter speed is the bigger problem. Regarding positioning, walking around and constantly repositioning is usually the best approach because you are trying to capture that split-second dynamic action. If you wait in one spot, you are only getting shots from one specific angle, and since the cars are moving so fast, waiting usually means missing the best part of the run. Get close enough to the action that you can anticipate where they are going next, then move into the shot, take the picture, and reposition before the next run starts. Just keep the shutter speed high and stay mobile.

Counterpoint on the positioning question - I mostly plant myself at one feature and let the course come to me. The fastest corners or the slalom are where the cars lean and the wheels turn, way more photogenic than launch shots from the start line. I pre-focus on a cone about 30 feet out, wait for each car to commit, then fire a burst of 5 or 6 frames as it comes through. Out of a 60 second run that nets me a keeper maybe every third driver, which is a fine hit rate. Walking the whole course means half your frames end up from bad angles anyway. If your lens hunts when the car changes direction, a fixed spot solves half of that too, since you allready know where it's heading.

I shoot my nephew's kart races and had the same wake up call with shutter speed, though karts are slower than autocross cars so maybe I can get away with less. One thing that helped me was shooting in bursts and just accepting I throw most of them away. Also kind of related question, when you guys pan at those faster speeds are you rotating from the hips or just swiveling the upper body? I tried following the kart at a slower shutter last month and my arms seemed to wobble more than anything, wondering if my stance is part of the problem.

This sounds like my problem exactly. I shot a mud run with my camera last year and every picture looked fine on the little screen at the time, then I got home and they were all soft. Is there a way to check if a shot is actually sharp while you're still there, like zooming in on the screen or somthing? I just assumed if it looked ok small it was ok.