Someone explain porteur geometry to me

Why does carrying a load up front require a bike with less steering trail? Is it just to reduce wheel flop when the bike is stationary or does it help when the bike is moving as well?

I’m not finding it now but Kogswell had a write-up (VBQ article?) of the process they went through to arrive at the various fork version for their porteur frame and what was suited for what end use.

Think of it this way: since your steering column is in a semi vertical/semi horizontal axis, any weight on top of it (or in front, if you will) will tend to make it flop, the further you move the wheel away from this axis (increase rake), the more in-line it will be with the weight being carried. Also, the steeper the angle is, the less the weight it’s carrying will want to fall over on the side. This is true when going slowly, and to a lesser extent when going fast (since less turning is require to correct balance). Hope this helps.

kogswell dude is strange.
man, he really could have gone much farther with the whole kogswell thing, but.

Well, actually selling those ISO cogs he was advertising and answering questions about his stuff on BFSSFG would have been a start.