Not as much as you'd think.

Assume it's a semi circle at each end and then two parallel straights.

The straights are the same irrespective of inner or outer line.

So you now have two semi circles = a circle. Circumference of a circle = pi x diam. Diam is the diam of inner circle, call it D, any other is D+d where d is the 'extra' diameter. So, the difference is

Pi x (D+d) - pi x D = pi x d.

So the line that's half a metre wider (in radius, hence diam is 1m different) makes the track about 3 metres further. Significant when the race is won by cm or even mm, but not 'vast' in absolute terms.

[Edit] Just looked it up - the diff between black and red is 0.9m, hence difference is pi x 1.8 = 5.7m approx