I am not setup to ride the slam on my TT bike, but I always did ride this position on my road bike.
I'm moving myself forward now on my road bike since my focus is triathlon and my road riding is in support of that.
I want the horizontal back and if my hip angle goes tighter than 90 degrees I have trouble breathing.

When I rode that position on my road bike it gave me more upper quad and glute involvement in my pedaling and it suited me. It's not a high cadence position, but more of a gear masher position. I do have to say that running is harder after blasting the lower quads than it is after blasting the upper quads/glutes area.
I say this because I have a lot of experience with heavy weight workouts and running/walking afterwards. Very hardcore squat workouts don't affect my ability to run much (upper quads/glutes), but leg extensions (lower quads) can make me unable to walk and even stand for a few minutes.

I would love the slammed position in triathlon if I could only get aero and breath at the same time.

Thanks. Did you set yourself up using some guidelines regarding angles to strive for or did you have someone help you?

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Formerly DrD

No, not at all. I hold professional fitters in high regard yet never have gotten fitted.
It seems as though it would be hard to determine whether the slam position is the right way to go. Are certain people faster this way only because it's the way they've trained their bodies to be efficient, or vice-versa? It's a bit of a cause/effect conundrum.

Ideally we'd be able to run the 'big slam' position with a level back, but this is a position that is way outside the UTI specs. It almost becomes a reverse recumbant. You'd end up with a much longer top-tube and crazy 90 degree seat angles (or more).

I don't think it's feasible to ride the slam position on a tri bike or you end up sitting far too upright and catching too much wind. It can be done if you ride more of a 'multi-sport' position though. I can easily set up the slam position on my mtn bikes for instance...but even there I'm moving my seat back forward to get myself in a position that is closer to my other bikes so that all of my riding is more specific to my TT position.

I've been playing around a bit with my position and riding steep has been a problem for my neck. I'm currently riding a Titanflex Transition that gives me some flexibility to effectively change the top tube length/seat angles.

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Formerly DrD

The best description of the slam position is found on pages 59-61 in Leonard Zinn's book "Zinn and the Art of Triathlon Bikes".

Particularly interesting is John Cobb's comment that after testing thirty riders in this position he has seen no aero disadvantage as he feels that the rider is in an aero shaped "egg" sort of position.

I will check it out. Great timing- I just bought that book this weekend.

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Formerly DrD

My guess is that he's referring to the upper body staying mostly at the same height and the rider sitting more on their sit bones and compensating for this weird angle by rounding the lower back.
I've seen a lot of young, flexible riders in this position, but my degenerative discs don't let me take that position. If I ride slammed, I have to rotate forward on to the nethers. When I'm in great shape I could handle it as there's little weight on the seat, but a leisurely ride can be painful.