Looking for some sizes advice for my first ever roadbike, any owner of the r-081can help me here?
my inseam and height is 82cm and 173cm, should i go for the size 52 or 54?
Look at the picture above your comment.
That is the set up for rider with height= 169cm inseam=79cm. on frame size 49 using 100mm stem at -10 degree.
the headset cap are 7mm tall and then 10mm aero spacer under the stem. Crank length used is 165mm. (it affact how high the saddle should be, if i use 170mm crank i'd set the saddle 0.5cm lower.) The saddle height is not very accurate as i actually raise the seatpost up further for 0.5cm after
i take the photo. (so the picture show the saddle to be 0.5cm too low. negligible but just make sure i say it)
The rider(myself) is 4cm shorter than you but with 3cm shorter inseam means my torso is only 1cm shorter (don't know about arms length).
52 is 0.6cm longer and 1.7cm taller than 49. -> i can fit this size too with no spacer and thin-ish (~2mm) headset cap and 90mm stem*
54 is 1.0cm longer and 3.5cm taller than 49. -> the headtube is just too high for me.
*: Length is something to consider more than just bike's reach difference because the head tube are 71,72,73 degree(for size 49,52,54) so any spacer under stem also effectively shorten the reach down. for example if i use size 54 i would need 80mm stem rather than 90 (100-10,different in reach between 2 sizes).
the first comment of this thread show size 52 with 80mm stem but lower spacer than mine. (for the look comparison)
if you use size 54 and your arm are similar proportion as me and OP, you'll end up with stem length 90mm (at most) or less (more likely).
So i'd strongly suggest 52 rather than 54 except if you plan to ride with very high handle bar and short stem then 54 can reduce spacer needed under stem.
But choose it yourself.