"I'll try to play it by ear, see how I feel, I've done races of a week or ten days before, so I know a little bit what to expect," Carthy told Cyclingnews before the start.
"If I get to the end of that period ok, then I’ll try to sustain it for another block, and so on. I've got some good guidance in the team, there's plenty of riders for advice and to give me a bollocking if I do something wrong. It's a good mix, I'm in good hands."
Given the Vuelta is the biggest race they will do in the season, Caja Rural-Seguros RGA have brought their 'A' team here, with Carthy saying: "This is the strongest team I've ever been with in the whole of the two years I've spent in Caja Rural."
Nor is the team's track record in the Vuelta lacking in success, with one high point a win in the 2012 Vuelta with Antonio Piedra on the highly prestigious summit finish of Lagos de Covadonga – a finish which features in this year's Vuelta as well. In 2015, Caja Rural - Seguros RGA snapped up the King of the Mountains classification in the Vuelta with Omar Fraile, repeating their 2014 triumph in the same competition with Luis Leon Sanchez.
After one full year with Rapha Condor-JLT and then two in Caja Rural-Seguros RGA, Carthy will join Cannondale-Drapac next season. The Briton has turned in some excellent performances this season, including ninth overall in the Volta a Catalunya and the overall win in the Vuelta a Asturias.
The Vuelta, though, is a whole new league for Carthy, and he conceded four minutes when he was distanced during Saturday's opening team time trial. Although it is Carthy's first Grand Tour, there are no plans for a scheduled withdrawal mid-race given his inexperience.
"It sounds like tempting fate when I say so, a lot can happen with crashes or illness, but I've got no plans to quit. Every one of our nine riders is here for the duration, we have the objective of finishing at the very least. We've got big objectives, big plans, so we'll see how things go," Carthy said.
"The team would love to win a stage, we've done it once before and to do that again would be pretty special. If we can get on the podium of any classification, that's a big deal for us as well."
Living on the other side of northern Spain in Pamplona, and riding for a team which is based in the same city, Carthy knows the roads in the Vuelta's Basque and Navarran stages midway through the second week the best. "I've studied the route as best I can. Obviously, I've not ridden a lot of the stages. Some parts of it round Bilbao I know, but I've never been to Galicia."
While his condition is good and he has some top results this season, Carthy said he will not be racing the Vuelta thinking that he has already achieved enough to ease back a little in the last part of the year.
"You could do that, but I won't. I'm here to race, and I'm not going to get complacent. I'll give it 100 percent and see what I come away with," he said.
After the Vuelta, Carthy may – despite the inevitable fatigue – take part in a few more one-day races before he leaves the Spanish team at the end of the year for Cannondale-Drapac and the WorldTour.
"Afterwards I imagine, if everything goes well I'll be pretty cooked and won't want to race for a while. But there are quite a few one-day races in France and Italy, still a few more opportunities to try and elongate the season before you finish," he said.
First of all, though, there's the Vuelta.