The ZR is a type of tremolo bridge designed by Ibanez for use in some of its solid body guitars. It was introduced in 2003 and is manufactured for Ibanez by Gotoh.
The ZR is a double locking tremolo and is the first Ibanez trem to feature a "Zero-Resistance" (ZR) ball-bearing pivot system. The use of ball bearing connections to mount the bridge to the body of the guitar (rather than a more typical two-post and knife-edge design) allow the ZR to effortlessly tilt up and down and return to its neutral position. The Ibanez ZR is one of very few tremolo bridges in the market relying on the ball bearings as pivots.
The ZR also incorporates a "Zero Point System" (ZPS) which is an extra set of springs which enhances tuning stability by helping to return the tremolo instantly to its "zero-position" or neutral point, which is the position at which the string tension is balanced by the spring tension with no pressure on the tremolo arm and the strings are in tune. The ZPS system also facilitates simpler set-up of the tremolo and easier string changes among other benefits.
The ZPS system is removable should the user want the tremolo to have more ability to "flutter" when it is returning to it's stable position.