I flipped the stem of my Giant TCX to the normal downwards position to see whether my flexibility has improved enough to support this position - and was surprised by how different the bike now feels.

The bike is a Giant "medium", which is actually quite small for my 5'9" (176cm) height and 34.5" (870mm) inseam. I've had stems from 90-120mm on this bike in an effort to find the sweet spot and had settled on 100mm (flipped-up) for the last few months. This gave a 6cm saddle to bar drop.

I started to feel a little bit hunched up, and thought an easy experiment would be to flip the stem down (but still with all the spacers), which would give me about 8mm more reach and 23mm more drop. Saddle to bar drop is now roughly 8.5cm.

What struck me immediately is not the bigger drop that caused me to flatten my back, but the fact that it made the bike feel *much* smaller.

More interestingly (to me anyway!) is the fact that my whole body also feels lower to the ground as though the saddle had dropped a couple of cm, even though it has not moved from its 760mm height (BB to trough of saddle).

The bike now almost feels like a toy! The medium size felt a bit small for me to start with (because of my long inseam, which required a higher saddle), but it now feels tiny - even though my position is now probably quite a bit more aero.

I'm wondering whether the lower arm & torso position requires any adjustment to saddle height or angle?

Could the lower bars compromise power output? I feel quite sluggish, but this may just be me getting used to the new position, and I need more time to get results.

Has anyone else had the experience of feeling like you are riding a completely different bike after making a minor fit adjustment?

I spoke with a pro and 3 x national TT champ about fit vs power. His take, from lots of testing: your muscles need to get accustomed to a new position but your max power output stays pretty flat over a range of positions, with a quick drop off after that.

My only unexpected experience with fit changes is increased comfort with more saddle to bars drop.

I've done a lot of physical therapy, what most likely happened is you hit the limit where your change in position caused some muscle groups to turn themselves off (when you're down that far). There's a reason why pros limit how far they'll go down for aerodynamics. Go down to far and your body can no longer use major muscles and you lose a lot more power from that, then you gain in aerodynamics.

You'll see some racers taking crazy racer positions going downhill to be as aerodynamic as possible, but they change back to a more normal position the moment they start pedalling.

Narrow handlebars are also good at making the bike feel "smaller".
The frame is not too small for you. I ride the same bike and am taller than you.
I wouldn't mess around with the saddle position either.

Maybe. But I always take several rides over a week before deciding on a change.

You might be feeling the difference in the way the hip adductor muscles are working. That's the second difference I notice with any change in bike fit, whether it's saddle height, handlebar/stem height, etc. The first thing I notice is how my neck feels. Due to an old C2 vertebrae injury and more recent shoulder injury, I have a very narrow comfort range. So every adjustment is a compromise between comfort and efficiency.

If my bar is too high, it's superficially comfortable but I'm not getting efficient use of the adductors. If it's too low, I feel cramped between my thighs and torso (I'm about 5 lbs over my optimal weight, not much of a gut). Right now it's just about perfect, about 2" below saddle height. I can't do slammed.

Yeah, I can feel even a 1/8" tweak in saddle height, fore/aft, stem height/length, handlebar tilt, etc. But again that's mostly due to the old neck injury and recent shoulder injury.

I read recently that Chris Froome is an ergonomic mess, with an awkward body that fights against his exceptional stamina and cardiovascular capacity. To me he looks like a pterodactyl that swooped down, killed the actual cyclist and stole his bike. His posture is awful. And apparently he needs frequent fit adjustments to be comfortable and avoid injury -- like, daily, if not throughout the day on a ride. Sometimes he prefers the saddle ridiculously low, but it works for him. With his elbows splayed out, head down, knees bowed and legs without normal extension, he defies every bit of conventional wisdom about bike fit.

Do whatever works for you and is comfortable.

Yes. Minor fit adjustments (or differences between bikes) can make bikes feel VERY different. I know the feeling of being a LOT lower, too - I've felt like I was crawling on the ground on a bike that felt totally normal the week before - I'm guessing that's more like what you mean by riding on a toy - something child-sized - rather than something fun.

Regarding sluggishness, I'd say yes, you may just need to get used to the new position to get the same or better results, but even if it's more aero and you do start to see better results, I don't think that means it's necessarily a better fit. More than how a bike happens to feel when I get on and start riding along, what makes for an ideal fit, in my book anyhow, is a smooth, natural feeling when transitioning between riding positions - going from cruising along on the hoods, to the drops, getting up on the rivet and sprinting, and riding out of the saddle and sitting back down, and a consistent predictability of handling response throughout the range of positions. Not only do I want to be efficient and feel "right" in each position, I don't want to lose a beat when making any transition, wiggling around "resetting" myself each time.

I get a substantial drop in power if I get the bars too low.

Could train into it somewhat but the only benefit seems to be possibly looking faster

while actually being slower.

When I increased my saddle-to-bar drop on my medium-sized Giant without changing the stem length, I had to move my saddle back to not have too much weight on my hands. I'm 5'9" with a 32" inseam.

I have around 1" variation in saddle/bar drop between some of my bikes. I really don't notice it that much.
Just because the drop changes it doesn't mean your torso angle does. That can stay the same and the variation taken up by the amount you bend your elbows.
See how much more/less you need to bend your arms to move your hands up and down 1". It is hardly anything.

I don't know what a Giant "Medium" frame equates to in traditional frame size but using the LeMond-Guimard formula, a 34.5" inseam would suggest a 58 cm frame. Ball park of course. If so, I'm guessing your reach is going to be too long in a 58. If a Medium is roughly equal to a 54-55 frame I'm guessing it would feel a bit small to you. For comparison, I'm 5'9" with a 32.5" inseam and ride what is called a "square" frame at 55 ST and 55 TT.

Just checked the Giant size guide. What a joke. Not even a TT measurement. Good grief.

Every bike I've looked at on Giant's site has the TT spec'd. Current TCRs are 550mm in medium.

This is what I saw on the Giant.com site......https://www.giant-bicycles.com/_uplo...frame_size.pdf

https://www.giant-bicycles.com/us/tcr-advanced-pro-1

Why would you rather a M/L when you are only using a 100mm stem on a M?
On your Roubaix do you have the lowest headset, flat bars, slammed -17 stem and it is still too high? You could still go to a track stem with even more angle.

Wait... a change to an 8.5cm drop is big? I think my saddle-to-bar drop is about 15cm, and I've got a 35mm stack under the stem.

My road bike is a 58cm, inseam is about 89.5cm. Torso is... short-ish, I guess, so I end up with frames that need like 22-24cm of seatpost showing to accommodate the spidery legs, and then the bars are way down just in relation to the saddle. I'm running the stem "all the way up," the steerer is uncut.

So I never feel close to the ground, really. The top of the saddle is about 110cm from the floor. If I had gone to a 61cm frame, it would have a nubby short ~90mm stem on it, which would look even weirder than it does now. Sometimes the frame looks tiny to me, then I see someone who rides a 54cm, and mine looks cartoon-like.

1 in more drop is not a small adjustment. You'll get used to it.

Personally I think it would affect (~1-2 hr) long continuous climb most when my hands are on the bar and in a more upright/relaxed position.

1 inch is a lot. I used to always be trying to run my bars as low as possible, until I figured out that when I run them low, I just quit using the drops, and am on the hoods and bar tops 95% of the time.

Right now, my bars are maybe 2" lower than the seat. which is optimal, and allows me to make full use of the drops as intended. If I go any lower, I will just find myself abandoning the drops, which is a real tragedy as it deprives me of many useful and comfortable hand positions. So these days I don't bother fighting it.

I have found I like bike with longer head tubes than I used to, Marco Pantani used to like bikes with large headtubes, because it allowed him to do much of his climbing in the drops. I think I'm coming around to this same conclusion.