The Adizero SL has an 8.6-mm heel-to-toe drop. In the running world, a drop between 8 and 10 mm is often seen as the safest bet for daily trainers. This shoe is on the lower end of that range, so we think it could be a good option if you're not a fan of shoes with a 10-mm drop or higher.

Finally, after years of careful development, it was time to introduce the world to the adizero. It was September 2008, the night before the Berlin Marathon. In his hotel room, Ethiopian long-distance runner Haile Gebrselassie laced up the first adizero Adios prototypes.