The first sector of white roads comes after 21km of undulating riding. With its 7.5km length and a net downhill of 138m, it's reasonably fast. You will barely notice the gradual descent, use this sector to get your rhythm.
You will reach the second sector after 68km, which is also part of L'Eroica, a vintage bike tour. However, unlike the bike tourers, you will be racing this 10.3km. This sector is almost connected with the third sector, just 1.5km of road until you enter Sector Three. This sector is undulating and climb at the end is 1km long with an average 5% incline.
The third and final white roads sector is the same as the first, but in reverse. You won't recognize it going in the other direction, and now uphill. Once completed, you'll descend back to Torrita di Siena before you hit the grand finale: the steep and challenging climb back up to Montepulciano and the finish on Piazza Grande.