I'm thinking on buying a CAADX 105 and I need help with the size of the bike (you can see geometry following the link).
First of all, these are my measures:
Inseam length: 82,5 cm.
Torso length: 66 cm.
Arm length: 67 cm.
Weight: 70 kg.
I currently own a Cannondale CAAD3 mountain bike, size M.
From my size, it seems I would need a road frame of 56, so a cross bike of 54 will fit me. It is my first non-mountainbike, so I don't have real references.
I went to a shop where they had the CX9 in 56, and it seemed giant to me. The top tube was just there 'in my parts'. So I'm almost sure that 56 is not my size: the seller said it will be more confortable for me, and that I should only buy the 54 if I intended to do some racing, but I think he was trying to clear stock...
I want the cross bike to replace my mountain bike in some forest tracks and occasionally to use it as road/touring bike. My mountain bike feels slow when I need to ride say 20 km on semi-decent roads to arrive to the forest tracks.
Then, today, I have found this sizing chart from Ridley: it seems I would need a 52-54... but I don't understand how they measure the legsize...
Schwin Twin, Rayleigh sports (1968), Bianchi (dont know year or type), Green fixed - built to my own desires, Cannondale CAAD9, Schwinn ss build, Fugi something-or-other.
I have read somewhere that riders 5'9" to 6 should go with 54cm, you are just over 5'9" so maybe try a 52. I have a 54 caad9 and I am 5'8" and i feel like it is just a tad too big. I think it will probably be easier to make the 52 fit if it is slightly too small than the 54 if it is slightly too large.
I would recommend looking at the effective top tube length (considering seat tube angle effects) and head tube length compared to a road bike that fits you and go from there. I don't think there's any magic formula like "road bike size - 2cm because bike sizes are often published as seat tube lengths which are (a) inconsistently measured and (b) virtually irrelevant compared to TT and HT. Just my opinion though.
I haven't tried it yet but a friend did and said it was kinda useful try the site wrench science it is suppose to be like put your size and preference in and it gives you an idea of proper frame size worth a try i suppose.