Because we all know that shimano have many options for pulley when come to change drivetrain, from each number of gears to serial in each.
Therefore come also one of simple thing, how long it least? and how about performance. Rear derailleur pulley have original slider bearing, that means that just one bushing slide to with amount of grease and prevent to get stuck. Therefore is no side stabilization, which means that with each gear you shift, pulley little move in one of side and shifting performance is little affected.
Question is, can we change all this? can we improve??
Simple answer is: YES WE CAN! in every part is place to improve. Here we found and test Cema Pulleys which use standart bearings and big advantage, is ONE pulley for many different.
before we need for 9 speed pulley for SLX one set for XT second set and for XTR third set so just for 9 speed gears we need 3 different. If we look from prespective of one shop is that minimum 15 pulleys to have in stock for suplly to customer.
Cema Pulley have better bearings and after that is one type pulley for all 9-10-11 speed which means that cover minimum 9 type of pulleys. and is already upgrade to your shifting preformace, because each of pulley have standart bearings.
Of course is also by standart cema Pulleys place to improve and we can always upgade to aluminium or ceramic bearings. More of that check in our shop.