Custom Steel FS
Commissioned before Pinkbike's Grim Donut, but designed in a similar vein (going extreme with angles, length, reach). In action since Mar 2019.
385mm seat tube
60.5 HA 82 STA (in mullet config, unsagged)
Ride comments: the seat tube angle is fine, especially considering that I have a mid-foot pedaling position. The HA makes the bike steer like a DH bike, especially noticeable at low speed. Once rolling, it feels fine.
The biggest issue is the weight and the long wheelbase. The long WB makes the bike less responsive to rider input--my weight shifts don't really do much, so it's very unforgiving to rolling off of drops at low speed. Go fast and stay centered is the name of the game. The weight balance is pretty dialed, and bumps don't phase the bike much at all. Cornering not really a big deal as long you remember the basics of traction. BMX moves not needed. The long wheelbase calls for much more durable tires (EXO/EXO+ are insufficient), strong brakes, and durable parts. It could use a motor, as it requires a lot of fitness to get it up to a speed that the long WB likes (shuttle/chairlift motor power works too). I believe that it also calls for a less-firm pedaling feel, so lower pedal kickback is a plus.
There's room to make the STA even steeper before the seated position matches the standing position. A dropper becomes more of a necessity though, as the saddle is in the space that I stand in when I'm standing on the ground with the bike between my legs at stopping points. As a bonus, it can allow more saddle drop without worrying about the rear tire contacting on full compression. I believe that my mid-foot position might be a bit extreme, and creating some bias in this. That and I believe that this improves suspension setup, as there isn't as much weight shift between sitting and standing. Normally, when sitting, there's more bodyweight on the shock and less on the fork, leading to questionable tuning choices like running lots of fork sag that has poor out-of-the-saddle pedaling and lack of support for the sake of making the fork do work while sitting.
I'm not so sure about any benefit in slackening the HA any further. I think the DH steering hampers the bike's low-speed handling greatly. The increase in front-center length from a slack HA is still very desirable and can improve the bump absorption vector for telescoping forks, but I wish for longer fork offsets to enable it. I believe the future trend will be to pair steeper HA with shorter offset for larger riders/bikes and slacker HA with longer offset for smaller riders/bikes. This config will give the larger riders more weight on the front and shorter and more playful/responsive WB and will give smaller riders a better-balanced bike that jumps, drops, and descends without so much need to shift weight rearward.