Let's offroad / mountain bike / mtb / ride dirt

There's gotta be a point, or else they'll become the exact opposite of a recumbent.

Really though, seat tubes can only get so steep without the riders injuring their knees, and the longest bikes if reach continues will only be rideable by the tallest riders with greatest mobility.

I listened to an interview with a guy that demos Geometron, and he was saying that 62° head angle was the absolute slackest, and beyond that was unridable.
He did make an interesting observation about stem length, in that when you draw a line through the centre of your grips they should intersect the center of your steerer if your riding such a slack bike (presumable he had a Mojo Rising fork with 0mm offset), which explains why when I had a 35mm stem on my bike I didn’t like it, as I ride with the bars rolled back quite a bit the steering was negative.

They seem to be reaching the limit now, actually. Pole Bicycles and Geometron have experimented with even more extreme angles and wheelbases than they have on their current bikes, then walked it back as the handling started deteriorating. Going past 62° (at least with a single crown fork) and a 1400mm wheelbase, IIRC, seems to be a general cut off point. Porter did make a downhill specific Geometron with a 59° head angle but it had a downhill fork, I think flex becomes an issue with more extreme head angles.

https://m.pinkbike.com/news/jack-readings-nicolai-geometron-dh-lourdes-dh-world-cup-2016.html

That bike still has a wheel base shorter than the Extra Longest size Geometron, I think. Which has a 62.5° head angle.

My Bfe has a 65° head angle and a 1220mm wheel base. Conservative by comparison but still reasonably LLS. Rides better than anything else I've tried.