My question would be....if wider are really faster on down hills (and I think that is a big if) why wouldn't pro's use them?
Could be as simple as the inefficiency going uphill is greater than down hill gains .
Or simply that wide tires are not faster
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Life is too short not to ride the best bike you have, as much as you can
(looking for Torpado Super light frame/fork or for Raleigh International frame fork 58cm)