It is surprising how much abuse a car gets on a trackday. I did one a few weeks back at Blyton in my MX5 and I managed to loose a centre cap and a wheel nut!

The brakes get so much hotter and the temperature transfers to the wheels and that's when the wheels become looser and the wheel bearings release some grease, good fun though not sure I could afford to take the XF on a track I did almost half a tank in the 5 and I was only on track an hour or so