Ask a Mechanic | Using OTTO’s Derailleur Tuning System Ask a Mechanic | Using OTTO’s Derailleur Tuning System Greg O'Keeffe2016-04-28T14:36:59-08:00 Collin asks, “My rear derailleur needs a tune up and I’ve seen OTTO’s Rear Ask a Mechanic | Using OTTO’s Derailleur Tuning SystemGreg O'Keeffe2016-04-28T14:36:59-08:00