I use them w/ the mtb deep in the woods when I know Im not going to be able to refill my bottles (yes I bring 2 full bottles on the mtb as well as the camelback). On the road there are many places to replenish my fluids.
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2010 Kestrel RT900SL, 800k carbon, chorus/record, speedplay, zonda
2000 litespeed Unicoi Ti, XTR,XT, Campy crank, time atac, carbon forks