The Irishman joins the British team from Tinkoff-Saxo, where he helped Alberto Contador to fifth-place in the 2013 Tour.
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A solid Grand Tour prospect himself – having finished in the top-10 of the Vuelta a España twice – the 30-year-old admits he is more than happy to play the support role to Froome.
“It has always been my dream to ride down the Champs Elysees with the yellow jersey in the team, that would be a brilliant success,” Roche told Press Association.
“My priority is to be at the top of the Tour and give my maximum to support to Chris.
“That’s something I agreed on when I joined, it’s something I wanted and I’m very happy to do that.”
Froome told Cycling Weekly recently that his whole season is tailored around the Tour de France, but rebuffed the notion that he was heading into the race as favourite.