What is the Unbalance Reduction Ratio?

The unbalance reduction ratio is one of the most important indicators of a balancing machine's efficiency and effectiveness. This ratio expresses the percentage reduction in unbalance measured on the rotor before the balancing process. Simply put, it's a measure of how much initial unbalance you've eliminated. A high unbalance reduction ratio indicates the accuracy and performance of your machine. For example, reducing an initial unbalance of 50 grams to 5 grams at the end of the balancing process means you've achieved a 90% reduction ratio. A good ratio, accepted in the industry and representative of efficiency, is generally 90% or higher.

This ratio is directly related not only to machine quality but also to the accuracy of the process. Adding or removing the correct correction weight at the correct location increases this ratio. At MBS Balance, the machines we produce aim to achieve high reduction ratios by minimizing unbalance even in a single balancing operation, thanks to high-precision measuring systems and powerful software. This saves our customers time and ensures their rotors are operating at peak performance. A high unbalance reduction ratio increases overall machine efficiency, reduces vibration, and extends bearing life, providing significant long-term benefits.

The Unbalance Reduction Ratio (URR) is defined in ISO 21940-21 as a performance metric showing how much improvement a balancing machine provides in a single correction, and is calculated with the relation URR = 1 - (residual unbalance / initial unbalance). A URR of 90 percent means that the unbalance is reduced to one tenth in a single correction step; 95 percent and above indicates that the phase and amount accuracy of the system is very high.

The main factors that limit this ratio are cross-effect between planes, angle and amount resolution, calibration linearity, and fixture repeatability. A low URR often stems from fixture looseness or incorrect plane/radius entry, and wastes time by requiring multiple attempts to reach the tolerance. MBS Balance machines offer a high URR thanks to mathematical plane separation and precise phase reference; thus most rigid rotors reach the target G grade in one, at most two, correction steps.