Redbullet

The general advice is that if you are between the sizes and you want more comfortable ride, you should choose the bigger size. However, apart from a higher (more comfortable) stack, the bigger size will come with longer top tube and longer reach that will stretch forward the body with possible issues of the lower back. How can it be fixed in case of “frozen” geometry with integrated handlebar (no replaceable stem)?

Eric F 

If you need a shorter reach, the solution is to replace the integrated handlebar with a new integrated handlebar, or bar/stem combo, in the size that is correct for you.

Redbullet

Yes, but those days of ordering bikes with customized components are gone. The producer sells exclusively the configurations on the website and don't want to switch to similar but shorter handlebar, even if they use it for lower size bikes.

Atlas Shrugged

By the sounds of it, you will be uncomfortable with whatever choice you make. To small and will be dealing with an aggressive position as well as a cramped cockpit. Too large you will be stretched out. If the manufacturer does not provide fit options time to move on.

Eric F 

There are still custom-build options out there. However, if you're locked in to that bike from that source, it may be that your only option is to replace those parts yourself (or with the help of your LBS) after you buy the bike. This is also a reason why buying a new bike from a LBS can be a better choice. They will help you with putting the right parts on the bike to fit your specific fit needs.

Redbullet

Not necessarily locked, but I had to exclude LBS due to their very limited offer (and still very pricey) compared to the offers of the producers over the internet. A few years ago it was easy to customize stem, saddle and cassette on an order for a new bike, free of charge. But now producers don’t allow that anymore and they excessively use integrated handlebars (I’m not a fan of those) even for middle tier carbon bikes. I was trying to stay on the budget – not tossing a new handlebar due to its length.

Eric F 

So, you want the customization capabilities of a LBS, but the low cost from a direct-to-consumer brand? It doesn't work that way. Part of what makes a LBC higher up-front cost valuable is they will help make you bike right for you, and will be there to help if something goes wrong with your new bike. Part of what keeps DTC prices low is the lack of customizable options, and easily-accessible customer service. Especially with today's modern bikes that often include fully-integrated cockpits, swapping out a handlebar or stem isn't just twisting a few bolts, it could be an hours-long disassembly and reassembly process. Labor isn't free. If you have a hard ceiling for your budget, there will have to be a compromise somewhere. My persoanl recommendation is not to compromise proper fit.

holytrousers

Why would a bigger size be more comfortable?

Eric F 

Longer tubes mean not as stiff (theoretically). My choice between too small or too large would based on the racer-boy mentality where you pick the smaller option because it's lighter, stiffer, and easier to maneuver (theoretically). However, a long carbon seatpost possibly offers more ride compliance than a larger frame. Also, a long seatpost and a long stem tends towards a hot-bike appearance, which I also like.

Kontact

Bigger sizes are, if anything, going to be stiffer for heavier riders.

mschwett 

why toss it? get the bike, get a different size of the integrated bar, sell the original one before you ride it. i sold the bars that came with my bike and another integrated cockpit that ended up one size off at a relatively small loss, something like 20% of the price. not a huge investment to get the right size, especially relative to the cost of a new bike. depending on how common the bike/bar is, you might even be able to find a used one and not lose anything on the deal.

elcruxio

My take on the whole size thing is that reach is a body proportion thing. And you can't compensate for body proportions. Once you've tapped out bike adjustments, ie. going to a shorter stem will compromise handling, the bike has to fit. If it still doesn't, it's too big and shouldn't be used.

Drop on the other hand is a mobility thing. Typically going a bit lower can be achieved by increasing mobility and/or easing other bike adjustments so dropping the saddle a bit.

Too much drop is also far easier to correct than too much reach by using a riser stem etc. I understand in this case that's not an option.

All in all, if neither size works with the given integrated components, I'd look for something else.

100bikes

Not sure where this comes from, but the mention of "General advice" being go to a larger frame is innaccurate - IMO.

I am not going out on a limb when I state that:
There is virtually no benefit to a larger frame than needed for a bicycle rider.

A stock bicycle with a frame to large will actually cause the fit to be compromised(stem length, crankarm length, etc)
resulting in potentially difficult handling.

Not to mention a larger frame has more inherent flex.

Since there are no standards for frame geometry, the design philosphy of top tube length
relative to frame size/standover height and frame angles are what the makes various manufacturers
frame offerings unique.

Materials, components and paint are pretty interchangeable.
I know of a Colnago that was painted Bianchi Celeste -with Bianchi decals - to meet the needs of a team rider.
Result - looked like a Bianchi and rode like a Colnago.
Rational - the Colnago "fit" this riders needs better than equivalent Bianchi, equipped exactly the
same and one with similar frame materials.
.
Keep in mind- the top bar always wins!

rusty
(45+ years selling and fitting bicycles)

Kontact

Going with a shorter stem isn't going to compromise handling. The difference between two frame sizes is generally one stem size - so a 100mm stem on the larger size and a 110mm stem on the smaller one. That's all.

Larger modern bikes aren't more flexy. I don't know where people get that idea. It isn't really true of old steel bikes, either.

Eric F 

In my experience, changing stem length isn't going to make a significant difference in handling, unless it's a really significant change. Many years ago, when I was young, fast, and strong, I went from a 110mm to a 130mm stem on my road bike at the suggestion of the coach I was working with at the time. I didn't really notice that my bike handled much differently. After taking a break from riding for 15 years, and getting back to it at over 50 years old, I found that my 130mm stems were a bit too much of a stretch for my current body. Going to 120mm did not give me any noticeable difference in the way my bikes handled. I've tried different stem lengths on my MTBs, as well, without a significant change in handling traits. I could see that going from 130mm to 80mm (or vice versa) might be significant enough to notice, but a cm or 2, not so much.

I agree 100% that bike fit is critical. Too big or too small beyond minor height/length/width adjustments is a bad idea.

elcruxio

Tapping out a road bike in terms of stem length for me is somewhere around 80mm. Below that it starts getting sketchy. Personally I prefer 130mm

Iride01 

On my 2020 Tarmac I was between sizes too. 56cm and 58cm. I went with the smaller size. More sporty handling, more fun.

I changed from the 100mm stem to a 70mm stem. And the first two or three rides were different feeling. But not any different than what I've experienced riding entirely different bikes. You just get use to it. Unless you are the type that doesn't like getting use to things and quickly put everything back like it was.

As for the OP about reach. Well reach to the bars from the saddle does increase, but probably not as much as the stack increases. Especially if one is willing to shorten the stem an overcome the initial difference of feeling they'll have until they get use to it.

Calsun

For me an off-the-shelf bike is a starting point. I often replace the stem and the handlebars on my road bikes and always replace the cassette. I always replace the pedals and grips and tires on my mountain bikes. With the exception of a custom road bike frame for touring I have bought my bikes from local shops and then had them make the modifications if special tools were required. Bike geometry has changed so much over the years that ther is no "rule of thumb" that can be relied upon.

For my part I do not want to be scrunched up on the frame and want sufficient distance between the seat and the handlebars. That usually means changing out the handlebar stem with a new one. I view this as a good time to upgrade the handlebars and handlebar tape as well. With road bikes I like to add additional material along the top of the handebars before starting with bar tape and this makes this section fatter and provides more surface area for my hands and minimizes hand nerve pinch from long rides.

Redbullet

I took a deeper look on the geometry:
"Reach+" is 18mm longer for bigger size (10 mm probably come from longer handlebar - call it “stem”, although it is integrated).
"Stack+" is 21 mm higher for bigger size.
Are those significant differences for comfort?

And regarding the “inseam” measure: if I press a little more, I am at the lower limit of the bigger size bike. Arm span minus height ratio - which I have just red that it counts - is +2 or 3 cm.

Eric F 

For me, 18mm longer and 21mm higher are pretty big changes. For a road bike, I might not be able to get the stem as low as I prefer, and might end up with a shorter stem than I prefer, as well. That said, my preferences might not align with yours. Part of the challenge here is that is sounds like you don't know what your fit preferences are, and how/if they might be limited by the frame's dimensions. This is - again - why buying a bike from an LBS has valuable advantages. They can help you figure out which frame size is right. For your online retailer of choice, it's a much bigger gamble if you don't already know what your preferences are.

ClydeClydeson

I have never heard this 'general advice' that bigger is better. It doesn't even make sense because every person has different proportions, flexibility, comfort requirements and expectations. Two people of the same height and body proportions are not necesdsarily a perfect fit on the same bike. I used to do fittings for custom assembled bikes and the fitting was always considered a 'starting point' - we expected and just short of demanded the customer come back after riding to discuss changes to be made to get it closer to 'optimal'. Occasionally this even meant swapping the frame size or going from a drop bar to a flat or riser bar, or other such major alterations, but normally it would be switching a 90 mm stem to a 110mm stem or the like.

My suggestion is to take a tape measure to whatever bike you currently ride and find comfortable and compare to the published geometry specs for whatever bike you are considering.

THere is generally a range of 2 or 3 sizes that a person can fit with a bit of tinkering - the 'ideal' size, one size bigger, and one size smaller. THe difference between two adjacent sizes is generally only a cm or two on any dimension, and this can almost always be compensated for with adjustments or a swap of standard size components. If you have a bike that is comfortable to ride for the distances you want to ride, and the bike you are considering is available in a size that is within a cm or two in most dimensions, then it will almost definitely be workable.
If your you feel your current bike is NOT comfortable enough, try to estimate what adjustment - bar height, reach, saddle fore-aft, crank length, etc -needs to be done to get it closer to what you think would work better, measure that bike and see if an available size of the new bike you want would bring you closer.

Iride01 

Reach in geometry charts is measured from the extended vertical centerline off the BB horizontally to the head tube. Stack is from the horizontal extended centerline of the BB to the roughly the top of the head tube.

Of course you did use the term Reach+ and Stack+. So maybe you should enlighten us or at least me as to what they say those terms mean.

Redbullet

I found these terms on the geometry elements of one producer, below the standard terms without "+". I googled the terms with "+" and i understood that they are measured similar to the original without "+", but not up to the head tube, but up to the center of the handlebar at the point it clamps to the stem (or it does not clamp, if it is integrated). I understood that is a more practical way of measuring, which takes into account the dimensions of the stem, spacers, etc.That is how I deducted that 1cm difference of the total in real reach (reach+) comes from a longer stem (well... integrated). I hope you get the explanation despite my imperfect English.

Redbullet

Agree. But not only that prices at LBS are 15-20% higher, but they have a very limited number of options, not covering what I am searching for.

Redbullet

The main issue here is the integrated handlebar: you can not work on stem length to reduce the reach if you need (and I have the feeling that modern bikes exaggerate with long reach; even the pro's are less stretched...). So, you end up either with a long reach (bigger size), or with a huge saddle to bars drop (smaller size). It is worth to remember that steerer is also fixed, you can not add any spacers below the stem.
I should add here that my body proportions are absolutely normal, so normally it should not be a problem to find an "out of the shelf" solution, but I'm still struggling with that.