The first big challenge for Bradley Wiggins and Chris Froome (Sky) is today's 19 kilometre ascent to a summit finish at Manzaneda, a ski station in Spain's remote north-west region of Galicia.
The climb has never been used before in the Vuelta a Espana, although it was occasionally used in the now defunct Tour of Galicia.
Compared with the two previous ski stations used as mountain top finishes in this year's race - Sierra Nevada and the Covatilla - on paper the climb is not as hard. Sierra Nevada is far longer and finishes 2,000 metres above sea level, whilst La Covatilla had several 13 or 14 percent ramps.
In comparison, the Manzaneda has an average gradient of 6 percent, with its maximum gradient of 10. 5 percent coming after three kilometres and eight kilometres of climbing. Neither stretch is particularly long.
The hardest part of the climb is the first section: the road rises through the village at the foot of the ascent and then continues to rise steeply in a series of sharp right-hand bends that kick up hard - in total around six kilometres long.
However, there is a big false flat midway through, and barring a steepish section with two kilometres to go the rest of the climb is pretty steady and fairly gentle.
That's the good news. The bad news for the riders is that unlike the broad, well-tarmacked roads used on the previous two big climbs at Sierra Nevada and La Covatilla, the Manzaneda is narrow - barely more than a single vehicle's width - and very poorly surfaced. If anyone punctures, which seems more than probable, it will be very difficult for their team cars to reach them quickly.
Then there's the weather. Whilst the temperatures have plummetted from the mid-thirties in southern Spain to around 18 degrees, there's a strong possibility of rain, which could wreak some serious damage - particularlyif the near-galeforce winds that are currently blowing continue all afternoon,
The wind is probably going to be the most decisive factor on the climb. Manzaneda is exceptionally exposed, picking its way across the side of a scrubby, featureless mountainside for most of its middle section - very similar to the Covatilla, in fact. Could Dan Martin (Garmin-Cervélo) take a second win? Don't rule it out.
As for Froome and Wiggins' rivals, after his setback on the Covatilla, Joaquim Rodriguez (Katusha) again seems to be the most aggressive Spanish challenger. He has said although he does not know the climb he plans to attack and that despite being 3-23 down on Froome, the podium and even the win is still possible.
Vincenzo Nibali (Liquigas) is equally convinced he can still win the Vuelta for a second year running, too. Fourth at 33 seconds, on paper today's steady, draggy climb suits him better than Rodriguez.
Vuelta a Espana 2011: Cycling Weekly's coverage index
Bradley Wiggins: Rider profile
Chris Froome: Rider profile
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