[jyl]

I've never used aero extensions. Why are they less safe?

Speaking of aero riding posture, I've been trying to flatten my back. I think I'm reasonably flexible in the hips, my problem is more that my knees get too close to my torso when I'm low with a flatter back. My seat is usually pretty far back, to get enough cockpit length, and on my main bike, I can't drop the handlebar low enough, those things don't help. Maybe my midsection is also too ample.

On the gym spin bike, I've experimented with setting the seat all the way forward and dropping the bar as far as it will go, and it works okay.