Knowing what gear you are in can be essential
Imagine you are going down a steep descent, or approaching a dangerous intersection. You may be coasting and not certain of what gear you have selected, and there is a sharp turn or climb coming up...
Taking your eyes off the road or trail to see what gear you are in can be dangerous!
Easy to install -- if you can replace a derailleur cable, you can install the GearSight. See Installation Instructions for details.