I don't have the numbers with me (maybe someone else knows them, or knows where they can be found?), but higher and higher percentages of a cyclist's energy go into overcoming air resistance as speeds increase. I've seen charts for this, and it is dramatic. Especially at higher speeds, the limiting factor -- and the factor that is really slowing you down -- is air.

One reason fairings are not more often seen or used is that they were outlawed long ago (for many sorts of races), because of their clear advantages.

But commuters are not necessary 'beneficiaries' or recipients of these policies -- most commuters are perfectly free to use fairings if they choose.

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Does anyone know of sources or plans for fairings?, especially fairings for DF bikes?

(Partial fairings seem the most practical, but some full fairing designs might also be worth a look?)