Originally Posted by
cubewheels
There is no specific number, the more handlebar drop you use, the more aerodynamic you become (while keeping 90 degree bend at the elbows for least air resistance) up to a point where your back becomes almost horizontal.
However, the more horizontal your back becomes, you might start experiencing discomfort or soreness in the lower back area, shoulders, and the neck and your p. You may end up having lower average power output as well.
Those who are "comfortable" in large handlebar drop tend to have strong lower back muscles and high average power output. The position will cause additional pressure on your arms unless you have high average power which can offset that pressure. Definitely useful for racers but not for receational riders.
Youre 100% right.
To add to this, it makes most sense from an efficiency perspective to keep your weight in the saddle and ride upright when pedalling at a relaxed power output.
As you start to put more weight into the cranks, out of the saddle, and spin at higher cadences, you'll want to get pretty lower to offset weight transfer like you said.