Frame size problem.

Rawski

I'm new to road bikes and would like to buy a used one. I looked over the guides to help me find the correct size, but due to my sizes, it's a bit tricky.
I'm 175 cm (5'9") tall, 86 cm inseam, and my arms span is almost 180 cm (5'11"), I'm also flexible.
I found a formula based on inseam 86 x 0.7 = 60 cm frame size. Other guides gave me 56 cm based on my height. On some forums, some say that 54 cm fit them perfectly. People that sell used bikes, often in the description suggests a person hight that their bike will fit. But this is only based on the person's height. From what I understand, I can adjust some parts to fit the bike better, but some like reach, not so easy.  
Can someone put some light on what size I should aim for and maybe suggest what adjustments to make?
I can't just sit on the bike and give it a try to find if it feels comfortable, as road bikes are new to me and I don't expect to feel comfortable regardless of the size. I'm sure there are arms and legs angles that I should look for, but again I'm new to this and have no idea what to look for.

whyamihere

A 60 would be far too big. I'm 6cm taller than you, and generally ride a 56, though this depends to some extent on the manufacturer's specific sizing and the fit that I like. If you've never ridden a road bike, you're going to be best served by going to a good bike shop and asking them to help you, or finding somewhere that offers bike fitting services. Anything else is just guesswork.

def_defyr

It depends on whether you are looking at a frame with a straight top tube or a dropped one. But I would say, based on your relatively regular dimensions, that no larger than a 56 cm straight frame and, honestly, a 52 or 54 dropped (slanting) top tube. That should get you in the ballpark. You can adjust more if the frame is a bit small rather than vice versa.

But yeah, if you are serious, the above advice re a bike shop and fitting is spot on. If you can afford a bike fitting and to buy a new bike (even if it's not a high end bike) from a good quality shop, they will probably give you a discount on the bike, and it's in their interest to make sure it fits as well as possible, so they will swap out seats, bars, stems, cranks until it's just right. And if you go back after a month and things don't work they should continue to work with you for free.

joe_totale-2

I'm 6 foot tall and have about the same inseam as you.
I generally ride a 56cm frame or the equivalent depending on the manufacturer, it suits me well and has done for years.

It's easier to make a slightly too small frame fit by doing things such as using a longer stem than one that is slightly too big.

As stated above you really should go and try some different size bikes before making a purchase.

brundonbianchi

I reckon You’re between a 54 and a 56 in most manufacturers frame sizes. It depends very much on the frame type as well. Stack and reach are the 2 most important geometry measurements for most people, regarding ‘fit’. If the bike has a ‘compact’ frame with a curved top tube design, it makes things a bit trickier. To cut a long story short, if you want a sharper feeling, go 54, if you want it a bit more ‘relaxed’ feeling, go for a 56. Then play around with stem lengths and bar widths, until it’s how you want it. I would normally say get a bike fit done somewhere reputable, but that’s a bit off the cards at present.

dj58

Going just by your height as you have realised, does not take into account your arm, leg and torso length. All bike manufacturers frame sizes do not necessarily match, that is why frame stack and reach dimensions are quoted along with the other geometry measurements to help with fit and comparison.

A medium 54cm, medium/large 56cm or a large 58cm could all fit you. Things you can alter to affect a bike fit are saddle height and fore/aft position, crank arm length, stem length and angle, number of spacers above/below the stem for the length of the O.E. steerer tube, 2nd hand bike may have had the steerer tube cut down, and handlebar reach and drop. It is often said that it is easier to make a smaller frame fit than one that is too large.

When you find a bike that you are interested in buying, look up the geometry if you can or ask the seller to give you the dimensions, you could then draught an actual size drawing. You can also ask on here if anyone has that bike and what size they have for their dimensions.

https://blog.bikefit.com/how-to-fit-a-road-bicycle/

topsey_turvey

I'm 6'2" and ride a 58cm frame. Even a 56 might be too big for your height.
There really is no substitute for sitting on the bike and seeing which suits you best.
I have three frames, all the same size, and they all feel different when I switch around.
You wouldn't buy a pair of shoes without trying them for size, so why spend a lot more and not try for size?

DeVlaeminck

In most road bikes you will be a 54 - those that run small (Cube) maybe a 56. I can't see you ever fitting a 58 - I'm just shy of 6'2 and generally ride a 58 in most makes - or I'm bottom end of an XL.

You can shorten the reach by fitting a shorter stem though I wouldn't go less than 10cm, on a smaller bike maybe you'd go to 9cm . Some bars are also shorter reach and narrower bars tend to make it feel shorter too. Stack can be lowered if you have spacers under the stem but only raised if you have spacers above it. Well you can buy a stem with a different angle or flip it so it points up though some (ok me) aren't keen on the aesthetics of that.

N0bodyOfTheGoat

Given you're a bit shorter than me, but with longer legs and longer arms, I'd be surprised if you fitted a 58cm Cube Attain well.

These days it's all about stack and reach numbers, I suspect that for many manufacturers you will be a 52/54/56cm.

Rawski

Thanks for all the comments.
The problem with trying different bikes is that I'm not buying a new one. And I don't wanna go to the store knowing that I will not buy from them and use their fitting service. I'm new to road bikes and will start with used ones. If I get hooked, I will change my bike next year. I could of course ask different sellers with different bike sizes to try the bike first, but since I'm new, regardless of the size, it will feel a bit awkward, since the riding position is different. The bike would have to be way too big or small for me to notice that something is off.
I think that 54cm will be a good choice. Few of you said that it's easier to adjust the smaller bikes than bigger. And an overall suggestion from you guys was around 54 cm. I will start with that. Then with time, I will gain experience, found out what to look for regarding the position on the bike, will learn proper techniques, and all this will help me to be better prepared for next maybe more serious purchase.
Thanks again, now at least I know where to start from.
Cheers.