Shimano Ultegra RD-R8150 Di2 12 Speed Rear Derailleur bikebox Electronic shifting is the gold

Electronic shifting is the gold standard and more bikes are coming equipped with these groups

The best part of this product is the submergible pouch

Because of this

Bearings - Triple-sealed Cartridge & Needle

Shimano Ultegra RD-R8150 Di2 12 Speed Rear Derailleur bikebox Electronic shifting is the goldNow simplified with a single derailleur cage length, the Shimano Ultegra RD R8150 Di2 12 Speed Rear Derailleur packs Shimano's fastest, most precise shifting into a more approachable option. The single cage length is compatible with up to 34T low sprockets, making it more versatile than ever. Specifications Fastest ever rear shifting 58% faster than RD R9150 Compact design includes an integrated wireless unit, charger and switch LED status indicator