So I was just playing around with a tape measure and a calculator on the weekend, resurrecting some of my high school trig, and trying to figure out my effective seat angle.

I ride a 57cm Colnago with standard road geometry (73deg), with standard road bars and Profile Carbon-X clip-ons. The seat is slightly forward on the rails (certainly forward of the middle) which, as I understand it, would give me an effective seat angle of greater than 73deg.

So how do I find out just what that seat angle is? I thought of measuring the vertical distance to ground from the top middle of the saddle, then the distance from the same spot on the saddle through the pedal axle to the ground. This would give me two sides of a right angle triangle, so I could then use the sin rule to calculate the angle, right?

Problem was, when I did the calculation, I came up with an angle of over 85deg, and I KNOW that this is wrong.

Any help?