Mode 2 is designed specifically panning and so turns off the stabilization on the panning axis, that being horizontal (hopefully) for most auto races. What specific Nikon lens were you using and what if anything does it have that is comparable to Canon's mode 2?
If you were using the 70-200 f2.8 of Nikon they that VR yields an improvement equivalent of a shutter speed of approx. three (with VR) or four (with VRII) stops faster are confirmed. Canon states 4 stops with IS.
As an aside, many years ago before attending my first Formula 1 at Watkins Glen, a pro told me to go stand on a street corner and take pictures of cars and trucks using panning. This was the days well before image stablization. But with not too much practice the technique became very easy to master prior to race time.