snedden9485 wrote:Is there a way of measuring your sit bones?
El Cheapo Ass-O-Meter
Get a 2 kg bag of rice, empty into a large plastic bag (tie a knot in the top of bag). Then spread the bag out (so rice is about 1 cm or so deep) on a low seat or stool (low enough to get an angle typical of what your thigh makes to your torso when riding on drops). The pad of rice needs to be more tan 25 cm wide and 20 cm long. Sit in the bag. Find the two lowest points, and measure the distance between them.
Pine Ass Guages
Buy a length of pine timber around 1 to 1.2 m long, 100 wide x 20 to 25 mm thick. Cut into lengths from about 120 mm to 160 mm, in 1 cm increments (make sure cuts are square). Sit on each one from smallest up until you find the first that is fully supporting your sit bones - i.e. not hanging over the side of the block of wood if you slightly shift your weight from side to side (replicate angle as per Method 1). Then take this block of wood to bike shop and check it against each saddle - need a bit of a margin, 1 to 2 cm around the edges of the sit bone to get good support with normal riding movements. If you're really fussy, you could make the blocks in 0.5 cm increments around what you measure with the 1 cm blocks to get a more precise figure.
Although I'm only 75 kg, and pretty lightly built, I found the ponza too narrow for me - my sit bones are around the 140 mm mark and were hanging off the sides of it.