The Hour Record

That's a good 8cm from the inside of the black line (which defines the track length) and 20cm from the edge of the Cote d'Azure.

Riding further out doesn't have any effect on distance travelled along the straights, so we just need to take into account the extra distance travelled during the corners. Luckily the extra distance travelled is just the equivalent of riding in a circle with a radius of 20cm larger.

A circle of radius r has circumference 2*pi*r
A circle of radius r+d has circumference 2*pi*(r+d)

So the difference caused by riding a distance of d further out is simply 2*pi*d, which is independent of the radius of the corners in the velodrome, so this calculation applies to any velodrome.

So by riding 20cm from the edge of the Cote d'Azure they're riding an extra 1.25m per lap through the corners. Over 200 laps (of a 250m velodrome) that's equivalent to a whole extra lap.

Even riding 10cm closer in (i.e. still 10cm from the Cote d'Azure) they can gain half a lap over a 50km ride.

It's not all this simple though, riding further down the banking will require slightly more energy to be expended in keeping that low on the banking. I'll leave it as an exercise for the reader to work out the optimum track position in/through/out of the bends.