[jtbo]

You can't make bones much smaller, shoulder width is such that I hit door frames constantly.

Losing water bottle would help even more, but I don't use one to begin with, also no pump etc. but those are just tiny little bits with slight or no real effect. Things that you start tinker after big things are sorted.

Like driving position. Also most important is how air leaves, front is always less important than rear, surface area being of course most important, which will be sorted when new bars arrive.

But rear of bicycle is problematic area still, even simple fairings there will reduce air resistance a lot.

Width of fairing should be width of leg and rest of body, then taper inwards from the sides and down from the top side, to make air leave well, just as with car with kamm or boat tail.

Simply best however is getting rid of upright position, when I tested bending over the handlebars so that I was more or less in the position of triathlon cyclist I gained speed without pedaling in places where before I slowed down with pedaling.

From bicycle alone 10% reduction should be fairly easy, of course it will not have much effect, but when you get wind blowing against you with strong gusts, any small help is plenty.

However Trek bicycle costs around 10 000 or more, I think that you can get nearly as good aero with 10 if being creative and true recycling, by using materials otherwise would be put into garbage, like plastic containers of washer fluid etc.

Weight is then another thing, but that has not much to do with aero.

With helmet, you can easily add aero shape to your existing helmet, there is no need to buy new and add to consuming mayhem, you can get as good aero with almost no cost than those fancy helmets costing 400 or whatever they cost.

My measurements tell that aero affects from speed above 11kph when upright position, that is 0kph travelling speed on most days as there is going to be headwind that is more.

All those claims about no benefit before 25mph are in lab, with no wind, any amount of wind will reduce speed where gain is easily felt, typical wind gusts are more than 13mph so you get benefit even when riding 1kph.

This can be easily observed from coast down test I posted, testing was done at the morning with rare no wind condition, around 11kph slowing down started to be more linear, speeds faster than that had clearly wind resistance adding to slowdown.
So 13mph (20kph) being limit where effects can be felt barely is not true with upright position, maybe more true with triathlon position with already good aero and tiny human being.

If you cut frontal area to nearly half, it will have effect from very beginning of movement and that is close to what happens when you change driving position, it is part of aero improvements and part of mods to bike as you need new bars to achieve lower riding position.

I would say everything matters, some more, some less, cyclist remains however largest restriction, but mods to bike can make restrictions caused by cyclist to be smaller as well, that is what mods made by Grant-53 are doing, those are mods to bike, but are not making bike itself to be more aero, but are helping cyclist to be more aero. If bicycle would be measured with and without those mods it would probably have more drag alone, because of increased frontal area, but add cyclists in and frontal area is no longer increased and air leaves more cleanly, so it is improvement.

Because I live at very hilly area, here it is very hard to find even 100 meters of flat road, any improvement of coast down, with minimal added weight, is going to improve average speed and distance I'm able to travel, also when you input wind to equation it will improve those aspects much more than what it might first appear when looking typical examples that always seem to forget that rather steady head wind, which seem to find all these roads from middle of forests to travel on.