Shimano and sram specific 40t sprockets have been designed this gives us the following benefits which wouldnt be possible with a larger sprocket size or with a universal type design 1 precise matching of the tooth profiles and shifting points specific to each cassette 2 perfect mating of supporting tabs reducing flex and aiding shift performance 3 lower b tension adjustment is needed ensuring good shifting throughout the cassette range compared to fitting a 42t installation notes note 1 f