Help with sizing-
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  1. #1
    mtbr member
    Join Date
    Feb 2014

    Help with sizing

    So I'm trying to pick up a nicer fat bike now after my last one was stolen. I'm interested in a used Fatback Rhino FLT that I have found at a good price, but it's a size small(14). I used the calculator at [](, but I had to self measure. So the numbers are not perfect but they likely are within 1/8th of an inch of my actual numbers, think I did alright at accurate form.

    Actual inseam 31in

    Trunk 24in

    Forearm 12in

    Arm 24in

    Thigh 22in

    Lower Leg 21in

    Sternal Notch 57in

    Total Height 70in

    This returned Standover of 29.5-30.1in and virtual top tube of 22.5-22.9in for the XC fit, and the gravity and all mountain are slightly smaller figures.

    From their geometry page at [, it seems close enough.

    I've never really tried to size myself out before, just sticking with a medium previously which always seemed fine. But I'd really like to pick this one up if it's not going to be too small. Being 5'10" I would have figured that would be too small but the geometry of the bike along with that calculator seem to suggest otherwise.

  2. #2
    mtbr member
    Join Date
    Jan 2016
    I find that calculator to be OK for road but not so much for mountain. At 5.10 I doubt a small works at all and would not be surprised on some bikes you fit a large. Go to a local LBS and test ride a couple of bikes in various sizes and see what really works--a deal is not a deal if it does not fit. Note I am 5.11 and almost always fit a large but I have a 34.5 inseam so very different----but your long torso would indicate a need for a longer top tube even than me--note my top tube on a trail bike is 25--that 22.9 seems way off to me

    Again go ride as only you can tell

  3. #3
    mtbr member
    Reputation: Shredmonkey's Avatar
    Join Date
    Jan 2013
    Also 510 here, Id say no way. Checked out the geo. You should absolutely be on a medium if not a large. Dont get the wrong bike to save a few bucks.
    Just my $0.02 though.

  4. #4
    mtbr member
    Join Date
    Feb 2014
    Thanks guys. That makes more sense, and I definitely don't want something that far off. Figured I would check though since the numbers seemed alright and I've never used the measurements before. Sigh, haha guess back to waiting for something to pop up.

  5. #5
    mtbr member
    Join Date
    Jan 2016
    In the meantime hit the lbs and test ride a bit to get a feel for sizing---or try a couple of your buddies bikes on for size

  6. #6
    mtbr member
    Reputation: mack_turtle's Avatar
    Join Date
    Jan 2009
    That Competitive Cyclist fit calculator is useless for mountain bikes, at least for modern ones. It told me to pick a frame that is two sizes smaller that anything I could ride, and I am 5'9".

  7. #7
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    Standover is not a primary fit dimension, additionally. It's a secondary consideration. Note in the details of this fit calculator when you hover your cursor over the standover dimension. They're using standover as a stand-in for the STACK of a frame (height of the headtube, which is a major factor in determining handlebar height). This is not even remotely valid.

    Agreed with the others who suggest that this calculator is outdated. You can still dig some useful information out of it, though.

    I punched all your numbers back through to see what additional information it supplied with the results. It's important to note that the "xc fit" supplied a stem length, too. 8.8 to 10.4 cm. XC riders don't usually even run stems that long anymore. My road bike has a 90mm stem, though.

    Bike geometries have changed and stems have gotten shorter. I guarantee the fatback you're looking at comes with a much smaller stem. Unfortunately, the spec list doesn't say. It's probably fair to estimate that the bike will come with around an 60-80mm stem. Also note that the sizing info the calculator gives you does include the top tube length of the medium fatback frame. Still with a long stem.

    One thing you can do to help make the numbers from this calculator more useful for modern geo bikes is to consider the top tube length + stem length from the calculator with what the bike comes with. So the large could work with a shorter stem than the calculator spits out. I've used this method for my last 3 bikes (I use the wrench science calculator, which is similar to this one, except that it actually saves the measurements I input years ago). Less to determine the outright size I should be looking at (I've been around long enough that I know what size works for me - at 5'8, I'm USUALLY on a medium), but rather to determine the stem length I should be using for a given frame. It's actually worked fairly well to help me ballpark it.

    I've also worked in shops for awhile, sizing folks for bikes so I've got some experience measuring folks and sizing them up to the point that I can look at most people and get their bike size pretty close. For you as a long-torso/short-inseam 5'10, I'd say you're a solid large. As a long-torso/short-inseam person, you're likely to encounter some larges may have top tubes that you find uncomfortably high (the standover measurement). It's one of the drawbacks of having this combination of body proportions. Some riders in your situation buy a frame size too small to get the standover clearance they seek in the specific frame they want, but this is the wrong way of doing it. Doing this will result in a poor fit that'll suck to ride. The correct answer is to buy the frame size you need. Your choices are either to get used to a standover clearance that's initially uncomfortable (there are techniques for mounting/dismounting to help you with this), be picky and look for a specific bike with enough clearance (there ARE some out there) and as many of the other criteria you're looking for as possible, or have a custom frame made. Obviously the full custom route is going to be the most expensive. The other two options will probably require some amount of compromise.

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