"Now with BMC, I should be happy there," the 32-year-old Irish champion told CW. "It suits me. I'll be able to express myself again as an individual and also to help Richie Porte."
Roche's goal, as with Froome, is to support his captain to a Tour de France win. This year, Australian Porte fought over the final Alpine passes and reached fifth overall.
"I was in the hunt for a new adventure," said Roche about his move to BMC.
"BMC gave me a good challenge to help Richie in the Tour and then, I think I'll be able to give it a good go in the Vuelta afterwards."
Porte also rode for Froome and Bradley Wiggins before moving to BMC to lead its Tour de France team. Roche rode in Sky's black colours from 2015 to 2016.
"I always wanted to go to Sky, since the team's debut. I'm an anglophone rider and I needed to ride with Sky. It was a tick in the box and I enjoyed my two years, and now it's time for a new challenge."
Roche believes he will find a mix of racing different to what he had in team Sky and in team Tinkoff, where he worked for Alberto Contador.
"I came from Tinkoff-Saxo, which had a much more aggressive way of attacking," Roche added.
"Sky was more about, 'Let's make the race the way we want the race to happen. If it works, fine, but at least you try to control the race.' It's a different approach. With Tinkoff, it was, 'Where are the weakness and where are we going to attack?' In Sky, 'Where are we not going to get attacked and how are we not going to fail?'
Watch: Team Sky pre-race activation exercises
"It was great to get the two approaches, and hopefully now, I'll be able to bring that on to BMC. Richie already has many experienced riders around him, but I'll add to it."
Roche had his chance to lead Team Sky in the Vuelta and won a stage last year.
"When I signed with Sky two years ago, I said that I wanted to cross the line on the Champs-Élysées with the yellow jersey on my side. That was one of the most emotional days in my career,” he said.
"And my stage win in the Vuelta last year... I came into the Vuelta with a top five in my mind, but then I crashed twice. It took a week to get back. I had to fight mentally, and just to get that was a massive relief. The Vuelta was just not over after the first week. It was massive."
Thank you for reading 5 articles this month* Join now for unlimited access
Enjoy your first month for just £1 / $1 / €1
*Read 5 free articles per month without a subscription
Join now for unlimited access
Try first month for just £1 / $1 / €1