The roadlink lets you take a GS Shimano rear derailleur and use it with an 11x40t 11 speed mtb cassette. This is perfect for riders living in South Korea with its mega steep climbs. If you want to do the Baekdu Challenge, you need this.
-100% Made in the USA
-Compatible with Ultegra 8000 GS, 105 7000 GS, Dura Ace 9100, and GRX810 rear derailleurs.
-Should be installed by a REAL professional mechanic. You may need to add 1 or 2 chain lengths.