Hope 40t rex 40t ratio expander allows you to upgrade your existing 11 36 10spd cassette to give an 11 40 range key features adapts a 11 36 10spd cassette to give an 11 40t range t rex ring installs behind existing cassette replacing one of the smaller sprockets usually 17t shimano and sram specific tooth profiles and shifting compatible with shimano xt and xtr 11 36 10spd cassettes sram pg1030 pg1050 and pg1070 11 36 cassettes shimano and sram specific 40t sprockets have been designed all