Hello;

I have been riding a nominal 54cm surly crosscheck, which has a 56cm top tube. I have 2 other roadbikes that are nominally 53cm size and they have around a 535ish mm top tube. When I'm in the drops on the 2 smaller frames I am bunched up much more tightly than when I am in the drops on the surly. I am about 5'8" (meaning less than that).

Where should my knees be in relation to my elbows as I bomb down hills in the drops pushing for a landspeed record? Even on the large surly I can pull my elbows in and my knees will just graze them as a pedal.

How flexible are you and what type of tuck do you prefer? I actually find tucking like the 3rd pic the most comfortable for me since my back isn't really flexible. However it's definitely something you have to work up to before you hit 50 on a downhill.

When on the hoods with my forearms horizontal, I like to have my elbows just barely in front of my knees. So that's the amount of stretch I like.

I've done many coasting studies on long steady grades. First of all, I emphasize safety when descending. We non-pros aren't doing it for money on closed courses. So I have my hands deep in the drops with 2 fingers on the brakes, forearms approximately horizontal, chin ~2" off the stem, back flat, knees gripping the top tube, and elbows pulled all the way under my chest, as far as they'll go. On bumpy or technical descents, I lift my butt slightly off the saddle. Testing against other similar riders, this position is as fast or faster than the usual hands on tops that one sees, plus it's safer. On the same grades, I'm slightly faster on aerobars, but not much, maybe 1 mph at 40.

In a tuck, hands in the hooks, elbows can slightly overlap the knees. Usually doesn't affect pedaling, because the elbows are outboard of the knees.

Faster to pull the elbows as far under the chest/stomach as flexibility allows. Arms are round = big aero drag. Try it.

My arms are more like guy wires. I think I can curl . . . 40 lbs? Once.

My elbows and knees always overlap if I lean forward, even sitting on the saddle. I have a 56cm frame/565 ETT and am "about" 5'11" (meaning less than that!).

The reality is it is about 23" from my patella to ischial tuberosities, and about 14" from my elbow to the base of my thumb. Added together, it would have to be 37" from where I sit near the rear of my saddle to the handlebar position that I use for there to be no overlap. But there is always overlap because any position I use on the handlebars is less than 37" from where I sit on the saddle.

Nothing wrong with your bike size, but most brands are shipping their bikes with shorter stems to make them more comfortable for inexperienced, aged, or unfit riders. If you've been riding a while and feel like you want a longer stem, you're probably right.

Trying to dial your reach by modeling your position after racers in postures of extreme aerodynamic distress is generally pointless. After dialing in your saddle height, saddle setback, and back angle, look at the angle from your back to the humerus (upper arm) with your elbows nearly straight and your hands on the hoods, where they will be most of the time. Something like this guy,

who demonstrates the position while showing that he is somewhat overextended. Look in a mirror, or have a friend measure. The angle should be about 90 degrees or a little less.

If you get a significantly longer stem to increase this angle, it might change your balance enough to require slightly increasing saddle setback.