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  1. #1
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    Cheating a frame size with an offset seatpost

    First of all, hello to all. This is my first post here.

    I also new to mtn biking. My friends are into it and I am game to try something new so I went with them...Walmart bike and all.

    Fortunately I lived through the ride at Dupont State Park.

    Obviously its time to step up in equipment. Being the cheapskate that I am, I am looking at a used Kona Four 26" full suspension. Problem: This bike is an 18" frame and I am 5'6". Proper fitting would dedicate that I go with a bike that is 16" or 17" max. From my research the real issue would be the top post measurement. The question is, "Can I cheat that by using an offset seatpost?" (Do they even make such to reduce the distance from the seat to the stem post? I see a setback post online.) Should I combine this with a short stem post and shoehorn myself onto this bike or simply move on? (but it's such a beautiful bike and a great deal...)

  2. #2
    Workin for the weekend!
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    Short stem (40mm) and a straight post, with the seat cheated forward. A dropper post would offer you even more of the stability you would need, when you needed it.

    Jus, sayin...

  3. #3
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    dont get a bike thats the wrong size. period. Saddle for-aft adjustment is not for cockpit sizing but for proper pedaling position (kneecap vertically above pedal spindle at the 9 oclock position.); since seat angles vary. Even if you "cheat" and slide the saddle really far forward with an setback seatpost installed backwards, when your standing out of the saddle for aggressive riding and downhilling the saddle position is no longer a factor and you will feel stretched out and sketchy. BTW the real issue is the bikes "reach" (horizontal distance between bottom bracket and top center of head tube); not sure what u mean by "top post measurement"
    '14 rocky mountain altitude, rally edition
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  4. #4
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    If you have a bike that's too big, making it fit with a short stem is a good idea. If you are buying a bike, making it fit with a short stem is a bad idea. Keep looking.

  5. #5
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    Thanks to all for the insights. The right side of my brain said the same thing just as I typed the question. Too bad its such a beautiful ride. I'll move on.

  6. #6
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    A lot has to do with personal preference, and I don't think anyone mentioned that..

    My downhill bike I bought a size small simply for flickability, my AM bike is the "proper" size because I'm seated more and it becomes more of a factor. Depending on your muscular build you may be able to muscle around a larger frame and it would probably give you the benefit of some added stability if you get into some fast bits.

    I say buy it, and give it a shorter stem. Your new to the sport so you probably won't notice the frame size too terribly much. If you find after awhile it is indeed much too large, and you want to keep biking, you can always buy the same frame a size smaller (or a new frame!), swap components over, then sell the one that's too big.

  7. #7
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    Move on. Since you have no problem buying a used bike then you can easily find something on pinkbike or ebay that will suit you better.

  8. #8
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    If seat tube angle is the same between sizes, the effective rear triangle (rear axle, BB and saddle) will be the same in any case. The saddle position is adjusted in relation to the BB and doesn't need further attention once you've found a good setting.

    The differences made by a larger frame are as follows:

    - Standover height is increased, so you have less room between the top tube and your family jewels. (If you have long legs for your height, this may not be a problem.)
    - Headtube will be higher. You might need to slam the stem (no spacers between the stem and headset), which is by many considered an aesthetic bonus.
    - Wheelbase will be extended forwards. This reduces the risk of OTB and generally makes the ride more stable.
    - You need to use a shorter stem to compensate for added frame length. This increases steering precision and speed, which is desirable given the added stability of a longer wheelbase.

    So in my opinion a frame one size "too big" might actually be a good thing, as long as you don't run into trouble with standover clearance.

    It's never about the right bike size for your measurements, but the right bike size for you.

  9. #9
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    Quote Originally Posted by Saul Lumikko View Post
    If seat tube angle is the same between sizes, the effective rear triangle (rear axle, BB and saddle) will be the same in any case. The saddle position is adjusted in relation to the BB and doesn't need further attention once you've found a good setting.

    The differences made by a larger frame are as follows:

    - Standover height is increased, so you have less room between the top tube and your family jewels. (If you have long legs for your height, this may not be a problem.)
    - Headtube will be higher. You might need to slam the stem (no spacers between the stem and headset), which is by many considered an aesthetic bonus.
    - Wheelbase will be extended forwards. This reduces the risk of OTB and generally makes the ride more stable.
    - You need to use a shorter stem to compensate for added frame length. This increases steering precision and speed, which is desirable given the added stability of a longer wheelbase.

    So in my opinion a frame one size "too big" might actually be a good thing, as long as you don't run into trouble with standover clearance.

    It's never about the right bike size for your measurements, but the right bike size for you.
    I was trying to find a way to say all that, thank god for Saul. He's right, I have ridden bikes that were a little too big and a little too small. You can make it work if it's close
    I'm sick of all the Irish stereotypes, as soon as I finish this beer I"m punching someone

  10. #10
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    [QUOTE=Saul Lumikko;10862146

    The differences made by a larger frame are as follows:


    - Wheelbase will be extended forwards. This reduces the risk of OTB and generally makes the ride more stable.

    Up to a point. if the bike is really too long, you will be leaning forward to reach the bars, tehrefore distributing more of your weight forward on the bars; especially on steep downs it will be hard to keep your weight back, actually leading to more chance of otb. can cause back pain too.

    - You need to use a shorter stem to compensate for added frame length. This increases steering precision and speed, which is desirable given the added stability of a longer wheelbase.

    Again, up to a point. Stems can only be so short!

    I run a 30 mm stem on a bike thats just a tad too big, works out fine but after some time ive found handling to be kind of wierd. personally, i like the feel of 45-55 mm stems anything longer feels slow and shorter feels a bit twitchy.
    '14 rocky mountain altitude, rally edition
    '11 transition blindside

  11. #11
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    Check out what Mondraker is doing with their "forward geometry". Ever seen a stem with a length of 0 before?

    Practically speaking you are right, you can only play with stem length up to a point. But when your bar would touch the steerer within the stem, the frame size is probably so large already that stack and standover height are too big for you anyways.

  12. #12
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    "Proper fitting would dedicate that I go with a bike that is 16" or 17" max."

    There are many differences between frames of the same size of different manufacturers.
    Did you measure yourself and calculate the frame dimensions for your meaurement (e.g. with competetive cyclists calculator) and compare that to this frame's measurements? That will give you an idea how much your are off and if you can make it work by using shorter stems etc.

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