Soma Double Cross riders - advice please

Discussion in 'Bike buying advice' started by zoomboy, Oct 15, 2012.

  1. zoomboy

    zoomboy New Member

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    Hi everybody, Thanks for all the great input so far about bike builds. I've still got a question or two......... I'm feeling the need to upgrade from my 'always felt a bit small' hybrid bike to a more do it all type of road bike/cross bike. The Soma Double Cross has caught my eye. Next in line is the Surly Cross Check. I have the tools and motivation to attempt a frame up build etc. looking at drop bars with STI shifters. My main dilemma is about frame sizing. The LBS has me sized at 56. Is that top tube or seat tube ?? My current bike only has 'M' stamped on it, no actual number, so I'm not sure how that equates to the two frames mentioned above. The bike is an Avanti Pioneer, about 10 years old and it has a flat bar. Vital statistics - inside leg (inseam) 33", height 5' 9 1/2", arm length - average plus a little bit. Has anyone with about my measurements built a Soma Double Cross ? What frame size did you choose and did it end up fitting without too many spacers under the handle bar etc ? Another thread seems to imply that going down a size to a 54, based on the top tube length of the Double Cross frame would be a way to go. Seeing that I live on the other side of the world from the frame supplier, I'd like to get the right fit first time around. The main plan is general fitness riding/shopping trips and maybe some light touring. I think that I would enjoy riding a lot more on a bike that didn't feel as cramped as my current ride. Thanks again. Any advice would be much appreciated.
     
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  2. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Definitely size bikes by effective top tube length and not seat tube measurements.

    It's a bit tough to compare an upright city style hybrid to a road or cross bike as your position will likely change a bit but start by measuring the effective top tube length of your current bike measured horizontally from the center of your headset to the center of your seatpost. Compare that to the geometry tables of your desired bike and consider the length of your current stem. Assuming a fairly normal 100mm to 120mm stem you could go with an effective top tube of maybe 20mm shorter or maybe 20mm longer but not much more than that for the same position and perhaps a couple of cm longer for a more laid out road position vs. a more upright city bike position. But assuming the bike simply isn't too tall (and neither the 54 nor 56 cm Soma is too tall in standover with its sloped top tube) then you can make the seat height work with the wide availability of long and short seat posts these days.

    I'm about your height with a bit less inseam but personally the 567mm effective top tube on the 54cm Soma would be quite long for me and I'd fit better on the 52 even though I ride 55 and 56 cm road bikes. Part of that is the super slack 72 degree seat tube angle on the Soma and it's likely you'll ride with a fairly forward saddle which effectively shortens the top tube but it's still surprising to find a top tube nearly 3cm longer than the seat tube measurement.

    Same thing happened when I bought my Ridley X-Fire but that was mostly standover height and I had to size down to a 52 which seems crazy small but it's a great fit when paired with a 120mm stem and I can actually clear the top tube while straddling it before a race. So start with top tube measurements when looking at frames, also consider standover height if going to a different brand, especially in cyclocross bikes as they often have high bottom brackets but seat tube based measurements really made more sense when bikes were all built with traditional square geometries that matched top tube length to seat tube length and make less sense today.

    -Dave
     
  3. zoomboy

    zoomboy New Member

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    Thanks for the info Dave. It will be very helpful. I imagine that I'll also have to account for the fact that the seat on my current bike is pushed as far back on the seat post as I could manage. It's about 2-3 cm back from neutral. Maybe I should measure my arm length too as I used to climb a lot of trees when I was a kid :) Cheers.
     
  4. alfeng

    alfeng Well-Known Member

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    In addition to what daveryanwyoming said, you need to decide whether you are only using the bike for "regular" riding OR may eventually use it for "racing" ...

    Because, if your current bike feels a little small, then (IMO) you really want to figure out whether it feels small because the handlebar is too-low-or-too-high OR the top tube is too short OR something else ...

    • perhaps simply putting a longer stem on your current bike would make it fit better
    • or, a high-rise stem may be in order

    I still have the Drops of my handlebars lower than most people prefer ... but, ONLY BECAUSE I was always comfortable when riding with my hands on the Drops -- you know, touching the floor with my palms flat & knees straight was never a strain.

    So, with all of that said, I am also 5'9" (but with shorter legs than you have) ...

    Here is a FORT CX frame that I had about 10 years ago ...

    [​IMG]

    I sized it according to the top tube which was, by my recollection, ~55cm (+/-) ... the top of the saddle is 28.25" above the center of the BB spindle. The cranks are 175mm.

    • suggestion: measure your current bike's set up AND take a tape measure to the bike shop so you can measure any bikes which you are considering and/or test riding ... AFTER you find a bike-or-two whose ride you think you like, then go back and set up your current bike, accordingly. Test ride YOUR bike. Go back & test ride the bikes at the shop(s), again.

    The slack(er) head tube compared to the seat tube means that the effective top tube length is shortened as the stem is raised.

    If I had it to do over again, I would probably have chosen a frame ONE SIZE smaller ... mainly to get the handlebars in a slightly LOWER position. That is, YOU also need to be aware of the stem height which different frames will allow ...

    BUT, since notions of racing are far away for me, I would not choose a Fort, now, because it is a "true" CX frame which lacks eyelets or water bottle bosses so the bike lacks the utility of the common CX-type frames-and-bikes which are currently available.

    BE AWARE of crank arm length on any "new" bike that you buy ... a personal matter, to be sure, but generally people with longer legs use cranks with longer crank arms (e.g., 175mm, or more)..
     
  5. zoomboy

    zoomboy New Member

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    Thanks alfeng. I did some measurements of current bike and found that the effective TT lenght is 56 cm + seat has been slid back 3 cm = 59 cm. Also have ridden a few bikes and found that medium/large sizes feel best for me. So I'm going with Soma Double Cross 56 cm frame. (= 57.6 effective TT length from their frame geometry table) Should be able to fine tune from there with stem length and seat position etc. In the process of amassing all the parts for the build and I'll get a photo on here when it's done.
     
  6. Muirenn

    Muirenn New Member

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    Wonder if someone could help me answer the same question.

    I emailed Soma, hoping for stack and reach, and they told me to look at effective top tube only, and go up a size if I want to be less aggressive. (I would say I'm more comfortable in a more aggressive position, but don't intend to race. Not anytime soon, anyway).

    Well, my Pinarello Quattro fits well, its number are:


    Quattro: 51.5 Size Seat Tube 53.5 (c-t) Top Tube 53.5 (TT) (This is actual, the only one listed. Stack 53.1 (S) Reach 37.8 (R) Head Tube 13.0 (HT) Head Tube 72 Angle (HT°) Seat Angle 73.7 (ST°) Chainstay 40.6(CS) Setback 14.5 (SB) And my measurements are: Height 170 (5'7'') Ins 84.5 (33.3) Tor 58.5 Arm 58.5 I use a 110 mm stem with a zero offset seat post due to high saddle height (73 center of bb to top of saddle) and inseam torso ratio. Need the zero in most bikes I ride just to barely get over the pedals. I was thinking 48 or 50. Any suggestions? From some of the comments, it sounds like 50 will be too big, but the 50 has the same actual TT as my Pina. I'll bring the measurements to my fitter, but he is an engineer, and the numbers are a little sparse. :( Here is the chart again.

    [​IMG]

    Thanks again. Thought it made more sense to add this to a developed thread rather than start a new one.

    Sheila Muirenn
     
  7. alfeng

    alfeng Well-Known Member

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    I believe that you are mis-interpreting the "geometry" for the SOMA Double Cross frame ...

    You need to ignore the "actual" TT length and focus on the effective (aka "virtual" or "level") TT length ... which means that the 48cm SOMA DC frame whose virtual top tube is 540mm is probably the better frame choice since I'm pretty sure that your Pinarello has a "true" (as in, non-sloping) horizontal top tube.

    FYI. If you were to set up the Soma DC with the same number of spacers between the stem & the headset then the stem & handlebars will probably be significantly LOWER than the relative differential between the top of the saddle & the handlebars on your Pinarello and you will probably find that you will want a shorter stem ... probably a 100mm will be the right length; but, possibly a stem as short as 90mm-to-95mm.

    Wider handlebars could result in the need for a shorter stem, too.

    FWIW. I have several bikes whose frames have vastly different sizes ... although there was a period when I was experimenting, with the exception of saddle height above the BB & the saddle's set back, I would say that all have ended up being set up essentially the same as what I was riding decades ago! Of course, that probably means that I got more lucky than I should have as far as setting up my earlier bikes ...

    Basically, to ensure continuity between my bikes ...

    • first, I establish the relationship of the saddle to the cranks -- this is regardless of the crank arm length & it isn't a "fixed" relationship to the spindle
    • then I measure from the middle of the REAR edge of the saddle to the rear of the horns on the hoods regardless of the width of the handlebars or the height below the top of the saddle

    When I get the measurement to within about an inch, I generally stop tweaking the fit ...

    • variables include handlebar width, bend, etc.

    The result is that 'I' don't notice when switching between bikes since my upper body is essentially at the same angle (probably within ~1º) & the angles of my shoulders/elbows/wrists are essentially "the same."

    To some extent, the frame size is (IMO) cosmetic ...

    Regardless, the rule-of-thumb in the past for CX frames is to size them ONE SIZE smaller than your Road frame (presuming the Road frame is properly sized for the rider) ... where I believe that "one size" typically referred to an "inch" gross difference in the seat tube length (a variable amount to the actual size difference depending on the seat tube angle) ...

    Hence, the 48cm Soma DC has about an inch smaller seat tube & it has a TT which is close in length to your 51.5cm (the theoretical c-c) Pinarello.


    • to state what may be obvious, a reason for the "one inch" sizing difference is to compensate for the higher Bottom Bracket which a CX frame will typically have when compared to a Road frame + the larger CX tire circumference & therefore to ensure that the standover height is approximately the same ...

    BTW. While my FORT certainly "fit" me, my too-late realization was that I would have preferred a frame which was "one size" smaller & adjusted the fit accordingly.
     
  8. zoomboy

    zoomboy New Member

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    Thanks again folks for your help and advice on my project.
    [​IMG]


    Sorry it took so long for me topost my result. The bike's been finished for a couple of months now.

    I ended up going for the size 56 frame. My height is 177 cm (about 5' 9 1/2") with average proportions.
    The fit is great and I've never ridden such a 'nice feeling' bicycle.

    Went with SRAM Apex groupset, Tektro RX5 brakes with RL720 cross levers, and 32 mm tyres.

    It's set up for general purpose work - go get the shopping, light touring, general fitness
    etc and I could'nt be happier.

    Would probably go with the next sized down tyres next time as the type of riding that I do is 95% road
    with the occasional excursion off road to avoid stopping at traffic lights etc. Have since changed pedals
    to Shimano SPD style clip in's.

    Cheers.
     
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