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  1. #1
    RoadBikeReview Member
    Join Date
    May 2012

    sizing help on a 48 or 51cm synapse carbon

    i am 163cm male..... 76 cm insean (level in groin measurement) with femur length length a little shorter than lower leg..... small size 40 (7) feet.... short arms, small hands, short torso

    i was previously on a 52cm tarmac.... low head tube and long tt didnt work for me so i am going to the synapse

    should i go with the 48cm or 51cm?

    my tarmac had a 12cm head tube and 9mm spacers and that was still too low but iam wondering which head tube would be best for , the 48cm has a 13cm ht (which is basically the same as the tarmac meaning i would have to run spacers on the 48cm), the 51 had a 14.5 cm ht... i would like to run the bike w/o spacers so i am leaning towards the 51 but i dont want to be too high.... however, my short arms and torso probably will needs more than the 48 will give

    as for seat tube, i am debating between the 74 deg tube on the 51 and the 74.5 on the 48... which one will give me the setback i need?.... i want the saddle to be in the middle of the rails or slightly forward, both for aesthetic reaons and for performance ones

    any other short guys like me riding the synapse? any feedback would be appreciated


  2. #2
    RoadBikeReview Member
    Join Date
    May 2012
    ok..... let me rephrase the question..... i want to get the size 51 cause i like the idea of having a slacker seat tube..... assuming i do not run any spacers, does anybody know how much saddle to bar drop i will have the on the 51?

    assuming that my cycling leg legth is 76, lemond suggests (using this just for reference i know that my saddle heigth will be 2-3cm lower) 67 cm from middle of bb to top of saddle so lets say my measurement ends up being 64cm from bb

    the 51cm synapse has a stack of 54.8cm.... adding on 8cm approximate for the headset and stem, the heigth to top of bike should be around 63cm

    do my numbers add up? based on that, with no spacers, my bars will be only a cm or two from the saddle, or are my calculations too conservative and i will end up having more drop than that?.... will i have enough drop? i know that is a personal question and to be fair i do not need alot b/c with short tordo and arms but i am wondering if the 48 would be a better fit?

    i had a 52cm tarmac and the long reach on that permitted me from being comfy.... it had a 12cm head tube, i ran the full 9mm of spacers but it was hard to tell if the issue was head tube length or excessive reach, or both

    any thoughts? unfortunately, my dealer doesnt have one in my size to test


  3. #3
    Reputation: Ruby13's Avatar
    Join Date
    Aug 2011
    I can give you my thoughts as my wife tried a women's Synapse in both a 48 and 51 and she's 157cm.
    Now the geometry might be a bit off I haven't checked from the men's model but my LBS had her try the 48cm vs a 51 in a Specialized Dolce as the top top is shaped differently. She felt okay but a bit cramped on the 48 and ended up with the Specialized in a 51 (liked the colors better).
    The reasoning is that you want to stretch out a bit and you will probably end up riding on the hoods most of the time. With the 48 using the same reasoning you will be more upright and not in a comfortable efficient position.
    In my case I have a 54cm Synapse and have a very bad back. While I was fitted the LBS told me to ride a while before I made any changes since I still felt stretched out to much. I ended changing my stem from a 120mm to an 80 that effectively shortened my reach which I think you are worried about. Now after riding over 2500 miles my body has gotten in a better position and I am thinking of putting the longer stem back on.
    So I "guess" my suggestion is to go with the 51, it will still be more upright and you can always make adjustments in stack height and stem length to dial in your comfort point.
    Hope this helps.

    '11 Synapse 3+

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