Well, last year I used one shot mode in manual, but I was using bigger apertures like 4.5-5.6 and high shutter speeds and it gave nice looking shots, but no motion in the tires.
This year I figured I'd use AI servo (still in manual) to keep focus on the cars while shooting lower shutter speeds stopped down, but for whatever reason I had lots of missed focus or blurry shots. This was at the exit of the international horseshoe heading into the kink. I got plenty of keepers but the ratio wasn't super.
Last year and this year both shooting the 1D III with 100-400L V1.