Originally Posted by Trakhak
They design road forks like that so the bikes will handle properly at speed. Bikes with short wheelbases and steep frame angles work best with forks with short rake, which necessitates tight clearance under the fork crown. The best-handling bike I've ever owned was my Bianchi Eco Pista; 75 degree head tube angle, almost invisible fork rake, fork crown clearance so tight that they had to file the underside of the crown at the factory. That bike was incredibly stable in a straight line, and yet turns were instantaneous.
OK I'm dense.
Head tube angle, rake and trail are all independent of fork length. Sure, for a steep angled head tube, you need less rake to maintain trail. And sure, if the fork length on a given frame is changed, so will the head tube angle; but if you are designing a frame from scratch, you don't have these constraints, so could design in a bigger clearance. Or am I missing something? Surely 5mm extra is not going to render the bike less useful?