Fentuz

Hi,
i m looking into gravel bikes, more specifically, planet x and cinelli but others could do too.

i am right on the limit between M and L or 54 and 56. So what should I do?
go for the shorter and fit a longer handle bar stem or go for the bigger and fit a shorter stem?
also, if I go bigger, is there and advantage to fit a shorter crank set 165/170 instead of 175?

thanks

dsaul

I would go bigger and use a shorter stem. That gives you more toe clearance to the front wheel and gets the front wheel a bit further in front of you for more confidence when descending on bumpy terrain. For the crankset, I would go with whatever you currently ride.

Fentuz

I sketched various configuration using the data from Cinelli

shoota 

Whichever you pick don't exceed your standover height. The other parts of the bike can basically be changed to fit.

prj71

You are over thinking this. Get the larger bike and put on a shorter stem. Longer wheelbase = more stable ride.

RocThrower

I'm between most 54 and 56 frames and never know what to pick. I paid for a fancy bike fit only to be told I could ride either size. I usually ride 56, but a few years back I built up a 54 under the advice of 'it's always easier to make a smaller bike bigger" and I ended up hating it. I never got comfortable on it, even with a 120 stem. The last bike I got was a 56 and it feels great. I have a longer torso and shorter legs, so I don't have much exposed seat post, but I'm very comfortable and like the handling. As far as cranks, most bikes in these sizes come with 172.5, and that's all I've ever ridden.

tdilf

I would go with the advice above assuming you can't go ride both sizes before buying

chas58

Bingo.

I was in the same place between 54 and 56, and mail ordering a bike.
I bought both, tried them out with various stems, and kept the one I liked better.
Seriously, if you are spending the coin on a new bike, its worth $50 shipping charge to try them both out
(FYI, I bought a Canyon, and the return shipping was $0. There was zero cost to me trying out two bikes).
Yes, stand over height can be critical (especially if you have a horizontal top tube).

I ended up with the smaller one because I liked the more lively handling, the shorter reach ultimately was more comfortable, and I liked the standover height.
remember, with more seat tube exposed, you are going to get a lot more comfortable ride with a good carbon seat post.
(I put a comfy high $$$ carbon seat post on a bike that fit me like a glove, but had very little seat post exposed. There was zero comfort benefit from the carbon seat post on that bike).
All things being equal, the shorter frame will be more lively, the larger one will be more stable.

good luck with your choice

mstateglfr 

figure out measurements of a bike that fits you well. then compare that to the geometry of bikes you like and pick the size that is closest.