Many riders in the 2017 Vuelta a España have elected to equip their bikes with super-low gear ratios in order to cope with the final, steep climb on Wednesday's stage 17.
The Alto de los Machucos comes at the end of the 180.5-kilometres stage from Villadiego, and will serve up gradients of up to 31 per cent and an uneven, concrete surface.
With the risk of grinding to a halt in the finale of such a tough stage, many riders will be using a tiny 34-tooth chainring matched with an 11 to 32-tooth cassette at the back.
Component manufacturer Shimano posted photos of chainrings and cassettes on Team Sky's Pinarello Dogma bikes on Wednesday morning, although it is not clear exactly what gears the team's race leader Chris Froome will be using.
Shimano-sponsored squad Team Sunweb also posted images of Wilco Kelderman's bike equipped with 34-tooth chainring and large 32-tooth sprocket on the cassette.
Kelderman moved up to third overall on Tuesday after putting in a strong performance in the individual time trial.
Note the use of a Shimano Ultegra Di2 long-cage derailleur, rather than the usual Dura-Ace. The shorter cage on a Dura-Ace derailleur cannot cope with the large 32t rear sprocket and subsequent longer chain length.
However, the front mech will still have plenty of work to do in shifting the chain between a small 34t ring and a larger 53t one, which will be needed on the descents of the Portillo de Lunada and Puerto de Alisas.
Some riders may also elect to swap bikes in the run-up to the climb, to benefit from higher gearing prior to tackling the Alto de los Machucos.
Swapping bikes at a crucial point in the race is a controversial move – riders risk having to catch up with rivals, but that may be more than balanced out with the advantage of having lower gears when it matters.
Froome currently leads the Vuelta a España by one minute and 58 seconds over second-placed Vincenzo Nibali (Bahrain-Merida), with Kelderman at 2-40.
This week's mountain stages will prove decisive in shaping the final podium positions before the race concludes in Madrid on Sunday, September 10.
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