Originally Posted by yonderboy

I used, given :
Radius of wheel : R
BB drop : d
Crank length : l
Q-factor : Q
Pedal length: p

Height of pedal at lowest point : d = R - d - l
End of pedal : e = (Q / 2) + p [ this is a little fudged, because it's not quite accurate ]

So with a right triangle, we're going to solve for the angle D.

That should be pretty close, unless I've forgotten my math.