I am 188cm and usually run 58cm frames. A lot of ppl I know who are the same height and very similar saddle height have been downsizing their frames and running a longer stem with spacers. My question is has anyone done this and actually felt like the bike handled better or are most people just chasing what pros and Instagram influencers are doing?
This is actually the opposite of the trend I’ve been seeing (people riding bigger bikes without headset spacers).
You’re getting a shorter wheelbase with the smaller bike, but the longer stem is slowing down your steering slightly, so I think the difference is smaller than most would think.
The bigger bike with the shorter stem usually feels like it responds to steering inputs more quickly, but maybe is a little slower to actually change direction quickly, whereas the smaller bike takes a bit more input at first, but then follows through quicker.
If you’re riding at really high speeds often, then a longer stem can be beneficial, but for those of us riding around 15-25 mph most of the time, I think the bigger bike is probably better. 
The problem with sizing down is that a lot of road race bikes still have really low stack heights (this is slowly changing). Yes, you can add headset spacers, but at your height, a 56 would still be really low in most cases.
Is there any reason why you’re considering this other than “Pros are/were doing it.”?
It seems to me the recent trend is to have frames with better geometries so that you don’t need to slam the stem and run crazy long -17 degree stems. The Escape Collective has documented that while some pros are still slamming their stem, most don’t and you see more of a distribution. This seems healthy.
I like using -17° stems on road bikes because with a HTA around 73°, you’re getting a stem that’s pretty much parallel to the ground. 
I think it’s unnecessary and ugly when stems are at an up or down angle.
Yea I agree it seems to be moving away from that but I think it will come in phases, at least based on the circle (bubble lol) I am in.
Pre-phase - Wout Van Art runs a size (or two) too small and a 140mm stem and slams it - I must do the same to be pro and aero
Phase 1 (we are here) - spacers are cool again, for my next bike I will run one size down but don’t need to kill my back and can keep spacers on
Phase 2 (we are moving here) - I am going to get my “true” size and run a “normal” stem and no spacers.
Phase 2.5 - Bike geometry slowly changes to accommodate the above with more “progressive” fit. No what 32in wheels would do to this on gravel side..
Based on my fit numbers - I can technically make a 56cm and 58cm work.
58cm would be slammed, 110mm stem
56cm would need ~25-30mm of spacers or so and 120mm stem
- just basing this off Tarmac geo-
basically wondering if the smaller frame “positives” (lighter, shorter wheelbase, “more agile”, etc) offset the spacers and longer stem.
and agree better geometries will fix this but it feels like we are still in the early innings there (new cannondale supersix for example actually decreased their stack and Tarmac SL9 geo didn’t change at all) so not sure what to do while we wait for bike geos to catch up
Nominal stem length is irrelevant, what actually matters for handling is wheelbase and front/rear weighting on the wheels.
Smaller frames with shorter wheelbases put more weight on the front wheel
Pros- change direction fast, feel nimble, ideal for bunch racing, more Aero at pro speeds ( smaller gap between front wheel and downtube)
Cons- twitchy and less stable at high speed on sweeping descents. This is why you see so many amateurs on “race bike geometry bikes” dragging their brakes down fast descents.
Larger frames with longer wheelbases move the weight distribution away from the front wheel
Pros- Stable at high speed, carves well at high speed on sweeping descents
Cons- slower steering feels sluggish when riding in the pack, feels harder to adjust and hold the wheel, you need to move weight forward on the bike to give the front wheel the grip it needs. Less Aero at the speeds pros ride at. (bigger gap between front wheel and downtube)
The real question I’d be asking myself is what kind of riding do I do? Do I want to feel super confident ripping down a 50mph+ descent on a frame size up, or will I be fighting my way through a pack of dozens of other riders inches away on the short twitchy bike? Pros spend most of their time doing the latter and have the handling skills to cope with the first.
I understand that stem length can be seen as fixed, for proper sizing, but it cannot be irrelevant. Stem length has at least as much relative power over handling as wheelbase and weight distribution.
Steering is degree per second over arc distance and cannot be separated from either chassis characteristics as they all influence each other. For a given typical marginal difference between stem and wheelbase, the stem has significantly more power.
If a given rider sized down 1-2 sizes, the wheelbase changes by a smaller factor than the expected stem length change, and has a smaller overall effect on handling.
Going from 58 to 54 Tarmac is Δ20mm WB and most likely >Δ20mm SL. The relative power of each can be calculated by the expected difference in hand displacement over steering arc as well as difference in minimum cornering radius at expected speed. The higher the speed the lower wheelbase relative power, because the minimum radius is that much larger and the steering arc is that much smaller.
Although it is the driven variable from these changes; Wf/Wr has significantly more power than wheelbase. At my weight, Δ between a properly fit 58 and 54 Tarmac ends up about 1kg more on the front wheel. This is relatively small to the total system weight but has a significant effect, as many of the people who stuck one of those burrito bags on their handlebars with a full load can attest.
Stem length change and the resulting weight distribution change will dominate the actual ride feel and handling mechanics far more than the nominal wheelbase change at typical range and road bike speeds.
This is the primary reason lots of people started riding, what looked like, child’s bikes (and almost boasting about how small a frame they were running)
I actually did this very thing with my most recent purchase of an Ari Shafer 3.0. I usually fit between a 56 and 58 and have ALWAYS gone with a 56. This time though I decided to go up a size, shorter stem and slammed. Loving it so far. Obviously that decision came with reviewing the stack height and reach of the frame…but yeah, it’s perfect!
I think it really comes down to stack and reach, it can’t just be a 58 is a 58.
I had a 3T Exploro in size L, and have a Caledonia in 56, they were almost identical in stack and reach.
I just got a Lauf Seigla in size M, the sizing difference between M and L is huge on this bike. The L would have been tall and long even slammed. I run the medium with a normal stem and 20 mm of spacers. The fit is almost the exact same as the Caledonia. I like a bit shorter reach for gravel.
I also lean toward smaller bikes, my very first bike was too big, my second bike was too small, now I only use stack and reach to buy bikes. If you have ever ridden “too big”, they feel weird, “bulky”, “boardy”, “not twitchy”, not sure best to describe it. Its easier to make a small bike bigger, than a too big bike smaller.
Awesome! How tall are you? That Ari looks pretty slick. What’s your setup for it?
I have a theory about this, it comes down to torso length vs top tube length. People with short torsos and long limbs and good mobility prefer smaller frames, people with long torsos and short limbs prefer larger frames. Both can be build up to the same stack/reach.
Same size as OP here.
I’ve ridden a 60, a 58, and a 57 road bike and 58 and 57 gravels. Also L, XL, and two other Ls in terms of MTB. When renting a bike somewhere, I always look for a large (~58) option. It is my natural size and it works independently of bike geometry. This is crucial!
All the bikes I mentioned were different models with different geometries. The 60 road was a Trek Domane (high stack, endurance fit). Shorter friends could ride it comfortably. 58 is a Trek Emonda, which is to date the best fitting bike I’ve ridden. More all-around racey geo. My current bike is a 57 ICAN A22. Longer, lower, slacker, aero fit and profile. It has felt too short or too long (or rather too low) on occasions, but it all boiled down to saddle fore-aft. The resulting changes in weight distribution have a HUGE impact on how the bike handles. I really had to nail that one to make the bike work.
One time I rode a size 58 Trek Madone. It felt quite weird at low speeds and only felt like it’s coming to life at speed.
On the gravel side, the 57 I ride is quite comfortable, but also on the verge of being too small for me. I couldn’t imagine riding a 56 with drop bars of any kind, my knees would come too close to the handlebars for me to feel comfortable. Toe overlap is also an issue.
All in all, IME it’s best to use true size and adjust from there. If anything feels weird, it often boils down to weight distribution, even more so on MTBs
Yeah, stack and reach are typically the gold standard here, especially when comparing radically different road bikes like the Domane and Emonda that @Savov7 mentioned.
The first real road bike that I bought when working at a shop was a Domane, and it was tough to get the bars low enough on it, but the size down had a really, really short reach. That bike also has a slack HTA, so using a really long stem wasn’t the best option. Looking at geometry is always useful.
When considering pretty much anything other than road bikes, I’d look at top tube or effective top tube lengths too. MTBs in particular can have wildly different seat tube angles, and so two bikes with the exact same stack and reach figures can have very different effective reaches.
When talking about bike sizing at a shop a long time ago, a coworker who was near retirement age and had been a mechanic for his whole life said he used top tube length for sizing. I always wondered why until I started getting into MTBs. 
I’m 6ft on the dot. I’m using an 80mm stem…which is shorter than I would typically use, but the wheelbase is longer than I’m accustomed to and, speaking with Ari, they recommended the 80mm (side note: best customer service I’ve ever had). I have Sram force w/172.5 cranks, pro discover carbon bars (42mm), and 50mm Dubnitals…probably will go larger once I get difference wheels just because I can.
I’m at the other end of the size spectrum from you where I started out riding frame sizes 54 and went down to 52 and now 51 with a longer stem, for me personally I much prefer the smaller frame size. I don’t use spacers and my stem isn’t crazy long, only 20mm longer than factory spec but for me it does feel better underneath me on the smaller frame. I don’t know if that’s the science, but I just know I’m happier on the smaller frame size. From what I’ve seen before the main reason that pro’s size down on the larger frame sizes is the weight difference and stiffness, which is small, but when you’re talking hundreds of dollars per gram at the world tour level it counts.
For me on the road bike, what matters is getting the right position of the bars relative to my saddle, which must be correct relative to the BB. With my saddle height and setback set correctly, I run a 10cm drop from the top of my saddle to the top of my bars. ATM I forget the horizontal distance from the middle of the saddle to the bars but as long as I can achieve that with a given size frame and reasonable stem and spacers, I’m good.
To throw another item onto the list - setback seatposts.
I agree that saddle and bottom bracket position are key. I’ve had to get 15mm to 20mm setback seatposts on my bikes to get the proper fit for best power and least injury potential.
I’ve found solving the saddle and pedal stuff first has been key to limiting any knee issues. Then layering in the stem and cockpit for optimal aero/comfort.
I’m 5’ 10" which is the sweet spot for being comfortably big on a medium and a large feeling like riding a barge. I wouldn’t make the decision based on fit charts - you have to go ride it.