sunshine09

The bike's size is S/M (manufacturer says for 1.68 cm - 1.77cm) and since i am 1.77 my supposed size is M/L(manufacturer says 1.73cm - 1.82cm, pretty much in the sweespot for me). Covid ruined the market so i cant pick sizes, it is what it is, I am not experienced so i cannot tell if the bike in question is a good fit but i do 150 - 200 kms per week on flatbar bikes and i know from experience that poor fit can absolutly destroy you after an hour on it. what should i do guys?

Andy Somnifac 

It will probably be fine. You can make plenty of adjustments during a fit (you're going to get a proper fit, right?). Personally, if I'm in between sizes, I tend to go for the smaller size. I greatly prefer that to the larger frame.

topflightpro

Maybe. It depends not only on your total height, but body proportions and how you like to sit on your bike.

sunshine09

why does it have to be so complex friends? bike fitting is an arcane art at this point, no matter how much i read and research on it, it is always so elusive

Bigbus

I have a 54cm and a 60cm and I find them equally comfortable for long hauls. Just set it up close and ride it. Then make adjustments to suit. Your body will make a lot of adjustments for you and within no time it just feels right. Lots of videos to get you in the ball park. Good luck and don't over think it.

surak

You can make a smaller frame work, but it may be aesthetically unpleasing with a massive stack of spacers and a positive angle stem. If you ride a flat bar like most, which is more upright than all but the least racy drop bars are designed to be ridden, then that kind of look will very likely be what you end up with.

Bike fit is not really that hard when you can test ride, it's only tricky when buying without trying. If you don't know what works for you, then maybe it's a bad idea to buy online.

big john

If you have a flat bar bike that you are comfortable on then you have a baseline. Compare the geometry chart of the bike you have to the one you are thinking about buying.

grizzly59

Check the crank arm length it comes with vs the M/L. If that's too short for your legs, I wouldn't buy it, no spacers or stem swap to fix that. If your legs are long for your height you may have comfort issues if you are at the upper edge of recommended height. What model bike are you looking at?

urbanknight

This. One factor that keeps me from going down one size on most bikes is seat tube angle. I have long thighs for my height, which requires me to set the saddle back a lot, and sometimes too steep of a STA keeps me from being able to fit it properly. But chances are you will be fine.

DaveSSS 

Fitting isn't that difficult if you know your saddle height accurately and have some idea of saddle to bar drop. I know exactly what range of stack and reach I need for a good fit, using my favorite 80mm reach bars. Height alone is a poor dimension to use for bike fitting.

I use a large 10cm saddle to bar drop, so I can ride a smaller frame than someone who thinks that 4cm of drop is a lot.

mstateglfr 

A lot of times, the geometry within a bike's sizes will change around the medium frame size.
The smaller frame will have a steeper seat tube angle and more relaxed head tube compared to the next frame size up.
that sort of thing.

You should check into this as the two sizes may feel and ride differently, even if your height can fit on both.

Kabuki12

For me on the vintage steel road bikes the seat tube length and top tube length are important for comfort. That is why , with long legs and short trunk, I ride racing bikes. I ride 63 or 64 cm bikes with short top tubes and not too long of stem. A tight cockpit is most comfortable.
I can get away with a 60cm bike(I have a couple) but I look for the correct size most times. Sometimes with vintage bikes you can make allowances with seat post adjustments and stem changes if it is that bike you really want at a price you can’t turn down.

delbiker1 

Everybody is so different there are too many variables to make more than a wild guess. You can make a frame set work for you, to a point. You state you would be going from ML to SM, basically a two size drop. There is a good chance you will feel cramped on that size. Personally, I can get more comfortable on a too large frame set with adjusted set up, than with the opposite. I am guessing that has to do with a longer head tube and the seat post being positioned a bit lower than would be usual. Remember, the smallest and largest measurements sellers give are the extreme ends of the rated size. Probably, not that many people at the extremes are going to be a real good fit for the bike, but might be able to get it there.

MAK

Arcane yes, but nevertheless very important. Ride with your seat too high or too low and after a while your knees are shot. Improper reach can cause back issues.

as for your original question...I've found that it's easier to make a too small bike larger (new stem, stem riser, setback seat post, etc.) than making a too large bike smaller in most cases.

jaxgtr

it is easier to make a smaller bike larger, but much more difficult to make a larger bike smaller. I tend to choose a smaller frame as I can make that fit my needs.

urbanknight

That may be true for you (and maybe even most people), but not for all. With my aforementioned long thighs and short shins, I need a laid back STA. Even with a 25mm setback seatpost, anything steeper than 73.5 seems to be no good for me, so I rarely fit on a 52 or 53 while my seat post isn't all that far out on a 54 or 55. With a 56 or 57, I can just get a 10mm shorter -17 stem and it works fine even though it looks ridiculous with only a few inches of seatpost showing.

DaveSSS 

I use a 32mm FSA k-force post. Saddle position set by KOP is not considered to be relevant by many pro fitters. I pay no attention to it. A 1 degree change in STA changes the top of the post by about 12mm. The change between sizes is quite often only 0.5 degree.

My latest two frames are the smallest I've ever owned. The stack is only 509mm, compared to my previous 527. With the 527mm stack, the 15mm headset top cover with a -17 stem worked. With the new frames I use a 30mm headset top cover and a 10mm longer -17 stem. The STA was supposed to be 0.5 degree steeper, at 75 degrees, but is wasn't. I can use a 25 or 32mm setback post, but the 32mm centers the saddle on the clamp.

eduskator

It will work as long as you get it properly fitted to your body. It might look odd (high seatpost / high stem), but some people do go with 1 size smaller for performance gains.

aliasfox

What's the bike you're looking at? Does it have stack/reach measurements? I'm 1.78m (5'10" in American), so I may be able to help with some specifics.
I ride a road bike with a stack of 575mm and reach of 382mm, with a 100mm stem and 5mm of spacers.

- From a stack perspective, I would consider this a reasonable 'Endurance' position. Race bikes in my size have stacks as much as 40mm lower (I've seen 55cm bikes with 535mm stacks), and you often see those with slammed stems (no spacers). Coming from a flat bar bike, I'd expect you'd want a stack measurement that was taller rather than shorter, which would push you towards the larger size. There ought to be room for spacers - my bike even came with 35mm of spacers under the bar, raising the handlebars to cruiser-like heights.

- From a reach perspective, 382mm is definitely on the short end, and paired with a 100mm stem (relatively short), I'm definitely more on the "comfort" end of the road bike spectrum. If you're coming from a flat bar bike, a shorter reach might be more comfortable for you, as you'll feel less like you're in a "superman" pose on the bike.

Additionally, body proportions and flexibility play a big part. I'm 1.78m, but I wear pants with a 30" inseam - basically, the shortest one can usually find off the rack. I imagine then that my torso is therefore proportionally longer than the average male, and because reach is less adjustable than seat height, that drove me to the larger size. I'm also not an especially flexible person - especially not at the beginning of each season. Last season, I started out with 20mm of spacers under the stem, ending with 10mm. This year, I've been able to drop that to 5mm, as I've been able to get more miles in, earlier.

So in your case:
- If you have longer legs than average (thus shorter torso), you may want to go for the smaller bike for the shorter reach, and vice versa if you have shorter legs
- If you are especially flexible, a lower stack height (smaller frame) can put you in a more aero position, at the expense of comfort.
- Sizing isn't absolute, and there's definitely a range of bar height/bar reach that can suit you, depending on your flexibility and comfort level. If you're not going to get a fitting, be prepared to play with stem spacers and bar rotation until it feels right. You may end up having to shell out for a longer or shorter stem, too.
- You'll find that seat position (fore/aft, height) is much less variable. Regardless of saddle, post, or frame, my seat position over the bottom bracket doesn't really vary - always within ~5mm for height, and probably just as small for fore/aft. You may need a fitting, or you may need to go out on a few short/easy rides with an Allen wrench to tweak the seat position until it's just right.

Best of luck!

ClydeClydeson

In my experience, most bikes are made in size increments small enough that most people could fit on two or three sizes acceptably with minor modifications (a cm or two more or less stem length or rise or spacers, saddle height or fore/aft adjustment). If you go more that one size away from 'ideal' then you might have to start getting non-standard parts to kludge a fit, like X-long seatposts or ridiculous riser stems or bars.

Also, everyone is different and what a manufacturer makes for the 'average' 1.77m person might fit your perfectly with no adjustments, or it might not.

genejockey 

The last NEW bike I bought was a Canyon Endurace. Canyon's bike fitting consists of height and inseam (5'11.5", 34.5"), and they suggested a Medium. I compared the stack and reach for it with the stack and reach of the 3 bikes I already had and which are all comfy for as many hours as I can ride a bike, and it would have required me running all the spacers under the stem as well as swapping in a 130mm stem for the 100mm that was standard on it. By contrast, the stack and reach on the Large was right in the ballpark of the other three, and would be the same bar-saddle position with 2cm of spacers under the standard 110mm stem. So I got the Large, and it fits great.