Charles S.wrote a review of SRAM X01 Eagle 12-Speed Rear Derailleur on September 5, 2018
Familiarity: I've put it through the wringer
I really hate to give a negative review, but I feel that this derailleur deserves it. Yes the range is great. The shifting performance does not seem as good as my 9 speed setup, but it is acceptable. The slow shifting is probably due to the wide range of the gearing. The real problem is that this thing is way too flimsy for a $225 component. First ride and a tiny twig gets jammed in the bottom pulley and the chain gets wedged between the pulley teeth and one of the plates that holds the pulleys. In 20+ years of riding I had never seen a chain get knocked off of the pulley like that. I assumed that it was a fluke. This happened a couple more times during the ride and continued to happen about every other ride. In some cases the chain would be wedged so tightly that the cranks completely locked up. The worst thing that happened was when the derailleur got forced into the spokes of my new Enve rear wheel. After this incident my derailleur was bent and my shifting was horrible. I bought the Park DAG and a couple new derailleur hangers. The original hanger was just barely bent. I bought the SRAM derailleur repair kit. This kit replaces the pulleys and the inner plate. The derailleur was still bent and the outer plate can't easily be straightened and I don't think it can be replaced. I bit the bullet and bought a new derailleur. I got 3 rides out of the second derailleur before another tiny twig knocked the chain off of the lower pulley and this derailleur got bent. Note that I have ridden some trails with big rocks and logs and never had a problem. The problem appears to be that the space between the plates is wide enough that the chain can easily jump off track and get wedged between the pulley and the plates. All it takes is a stick that is small enough to fit between the pulley guide plates and your derailleur is ruined.