The Essex cyclist in Spain's Movistar team supports Quintana this week in Tirreno-Adriatico. Already, he proved valuable by keeping Quintana in contention in the first day's team time trial and in position on the roads leading towards the mountains.
"The Giro's the first goal, but I'm 28 and I should be able to back up the Giro and then the Tour," Dowsett told Cycling Weekly.
"One should put me in good position for the other, and then the time trials in the Giro suit me more than the ones in the Tour, where they are much hillier."
Dowsett rolled up to the start podium for Tirreno-Adriatico stage six. Behind him, his Movistar team-mate and leader Nairo Quintana signed in wearing the leader's blue jersey.
Quintana is aiming for the Giro/Tour double this year. If successful, he would be the first to complete it since 1998.
"I'm just focusing on the Giro and not trying to think about anything after that,” Dowsett added.
“Everyone dreams of [of racing both the Giro and Tour], but the depth we have at Movistar is colossal so it's really tough. But if I have a good Giro then who knows and that may set me up for the rest of the year."
Dowsett beat Bradley Wiggins and won the Giro's time trial in 2013 and raced the Tour in 2015. Last year, shoulder surgery kept him out of the Giro.
Watch: Alex Dowsett's Canyon Aeroad for 2017
This season, he began strongly with races in Spain and the Middle East. He supported Quintana in the Abu Dhabi Tour. Now, in Italy, he is proving his worth for an eventual Giro and Tour place.
"Nothing's been confirmed yet, but hopefully," he said of the Giro.
"I've done my best for Nairo this week. We did a good job on Sunday in what was a chaotic race [to Fermo], all of us, it won't do my Giro chances any harm at all.
Quintana rode alongside Dowsett to the start line surrounded by journalists. He leads the race by 50 seconds over Thibaut Pinot (FDJ).
"He's happy as long as he has the blue jersey on his back. We have a good mix of climbers and flat land guys, we do our job and hand it over to the climbers," Dowsett said. "Everyone works really well together and others no egos or anything. We are all in to keep that blue jersey."
The Tirreno-Adriatico ends on Tuesday in San Benedetto del Tronto with a 10-kilometre time trial that suits Dowsett.
The Giro also has two time trials that Dowsett wants to aim for while supporting Quintana. One at the end of the first week covers 39 kilometres through Umbria and the second, on the last day, starts on Monza's Formula One's and covers 28 kilometres to Milan.
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