I don't know if there is any definitive evidence that wide forks are faster. The Speed Concept and P5 are good examples of a narrow and wide fork design that perform very similarly. The one "urban legend" is that the wide fork is generally faster with a Trispoke of similar 3 - 5 spoked wheel. The reasoning is that trispokes create a pressure pulse as the spoke passes between the forks, which is what causes the whoop, whoop, whoop sound. Widening the fork reduces the effect of the pressure pulse. Depending on the degree of the effect of wheel fork interactions it could be that the wide fork frames are less sensitive to wheel choice, but I have no idea if that is actually true.

This has been a debate forever about which is right. Cervelo has a different design philosophy; you definitely wouldn’t want to swap the fork on a bike as integrated as the P5.

Cervelo is trying to get wind to go around the fork assembly in that area whereas competitors with wider spaced forks are trying to allow air in between the fork and wheel/spikes.

Has there not been much testing to show who is right in debate yet? I'd be curious to see whether Cervelo or anyone else has tested it yet on a bike that was not originally designed around such fork. While it's true that the P5 is very integrated, there isn't anything complicated going on behind the fork crown compared to bikes that use wide forks. Intuitively it makes more sense to me to open a gap to have air flow freely instead of creating a single larger slug, for the same reason it's good to have at least one spacer between the basebar and arm cradles. I would also think that it pushes more air into the shins. Aerodynamics are hardly intuitive though.

The Speed Concept had a (for the time) relatively wide-stance fork. There's certainly more clearance on mine than on most road bikes of the time...

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ZONE3 - We Last Longer

Weren’t there definitive issues running the older HED tri-spoke on some forks? Something about a weird oscillation at high speeds?

I thought I read that here when researching getting one.