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  1. #1
    Superflying on Haven
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    How to : Extend a 400mm seatpost

    I have a short torso with long legs. When I need a bike, I'm in between two frame size. I need a medium frame (usually with a 80mm stem) for my torso but I would need a large frame (19 inches seat tube) for my legs. Most people always told me to get a large frame but I don't like the handling. Here is my solution that I share so that it may help other people who have the same problem and need an extension on a 400mm seatpost. This is for a seatpost with a 30.9 diameter.

    You need to "sacrifice" an old 30.9 seatpost and a 27.2. Cut a 27.2 seatpost (the lenght you need) and insert it inside the tube of the 30.9. Then cut another 30.9 and use it as a shim over the 27.2. It is supposed to fit very very tightly but maybe a bit of sanding will be necessary. Use some JB cold weld if necessary. As you can see on the pictures, it will extend your seatpost enough to avoid a cracked frame. My seatpost went from 400mm to 485mm (I know, I know... the Ritchey seapost has a particular shape at the bottom) . I used this trick for few years and I never had a problem.

    I hope this may help someone
    Attached Thumbnails Attached Thumbnails How to : Extend a 400mm seatpost-ext-1.jpg  

    How to : Extend a 400mm seatpost-ext-2.jpg  

    How to : Extend a 400mm seatpost-ext-4.jpg  

    How to : Extend a 400mm seatpost-131-3172_img.jpg  

    How to : Extend a 400mm seatpost-131-3171_img.jpg  

    Last edited by Menzo; 05-17-2010 at 04:37 PM.

  2. #2
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    I would take to a local machine shop and have it welded rather than JB weld. Good thinking!

  3. #3
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    Holy Long Seatposts Batman!

    Nice job and ingenuity. How about a picture of you riding it? I'd like to see what that looks like. Is that a weird request?

  4. #4
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    I think you need some riser bars, maybe a set from an old Schwinn Sting Ray.

  5. #5
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    I would prefer it to be welded together but then it would need to be heat treated ideally.

    I did a similar job on the fork for my cruiser, steer tube was to short so I found another steel steerer and added it on.

  6. #6
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    I did the same thing a few years ago on my fisher 292. I used hysol 9430 epoxy, which is 10 times stronger than welding. I would never weld the seatpost in this situation. JB weld is also a very good product, I've repaired lots of aluminum products with it and it has never failed.

  7. #7
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    Would that not put a sketchy amount of leverage (= flex) onto your frame?

  8. #8
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    Thats one of the worst examples of forcing a frame to fit I've ever seen. Congratulations. Your extending a seatpost and commenting on the 'handling' of a larger (one size, no differences other than slightly longer TT and more seat I'd bet) frame are mad. I hope your medical insurance covers you for the accident.

  9. #9
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    Good god man. You need the next size up frame! Your seat is way too high. You would be better off changing cockpit (stem big sweep bars, saddle forward) then monkeying around with the seatpost. Your seat is WAY too high. your center of gravity is compromised. Be careful!
    29ers are more fun!

  10. #10
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    Changing frame sizes won't change his center of gravity at all. That's based on how far he sits from the bottom bracket, which is independent of his frame size (assuming he gets his targeted leg extension on both sizes)

    Quote Originally Posted by tmccrohon
    Good god man. You need the next size up frame! Your seat is way too high. You would be better off changing cockpit (stem big sweep bars, saddle forward) then monkeying around with the seatpost. Your seat is WAY too high. your center of gravity is compromised. Be careful!

  11. #11
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    OP :: Seeing as you're using an inline post with the saddle centred on the rails, I'd think a "next size up" with an inline post would be OK for you. But YMMV.

  12. #12
    memento mori
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    I'd guess Seven,Moots,or even Thompson can and would make a custom post for ya.

  13. #13
    TR
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    I would love to know some body dimensions that needed that "fix".

  14. #14
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    You're right. I was thinking in terms of leverage. Moving the saddle (work) away from the fulcrum would make the bike top heavy. maybe mythbusters can tackle this one..lol
    29ers are more fun!

  15. #15
    Superflying on Haven
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    It's always funny to read the comments of people who don't know me, never see me and are not inside me, telling me what and how I should setup my bike. You guys should make kids so that you can teach them all your knowledge... They'll worship you

    Have you ever heard of a guy named RYAN TREBON. Believe me, my situation is ten times better than him

  16. #16
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    Clearly you're not manly enough to ride gnarcore stuff, otherwise that seatpost for the price of 3 would have failed a long time ago.

  17. #17
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    Menzo, what exactly are your dimensions? I have relatively long legs and short torsos also. My inseam is 32" and I'm 5'6" tall. I always choose frames based on top tube length and normally end up on a med/17"/18" frame.

    Have you looked into custom builders?
    "There are those who would say there's something pathological about the need to ride, and they're probably on to something. I'd wager though that most of the society-approved compulsions leave deeper scars in the psyche than a need to go and ride a bicycle on a mountain." Cam McRea

  18. #18
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    I would second the idea of getting a custom frame. Any builder can easily make a frame for you that accommodates your unique issues.

    Ingenious job making your seatpost work, but I'd worry about having something like that put together in the region by my sack!

  19. #19
    bonked
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    Or how about a woman specific frame. I'm not joking or trying to be a smart a$$, but women typically have longer legs and shorter torso, so frames designed specifically for women typically have shorter top tubes than 'typical' frames. And you could always put a decal over the model name if it's called something like the princess or the butterfly.
    Quote Originally Posted by banks
    That is one big f'n dude!
    Yes I am!

  20. #20
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    50mm stem and the next size up frame would be a better idea.
    get to know me thru my blog
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    spend $$ at my sponsors shop http://www.revolutionutah.com/

  21. #21
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    nice fix.
    now to more pressing questions. Where the hell do you buy pants?

  22. #22
    TR
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    Quote Originally Posted by singer
    nice fix.
    now to more pressing questions. Where the hell do you buy pants?
    At a pants party???

  23. #23
    Superflying on Haven
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    Menzo, what exactly are your dimensions? I have relatively long legs and short torsos also. My inseam is 32" and I'm 5'6" tall. I always choose frames based on top tube length and normally end up on a med/17"/18" frame. Have you looked into custom builders?
    I'm 5'10" with a 35" inseam. I'm right on the fence of Medium/large. I tried a large frame with a very short stem (60mm) and it felt like I was riding a Jesse James chopper bike. The wheelbase is too long, the handling awful.

  24. #24
    Plays with tools
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    Quote Originally Posted by Menzo
    It's always funny to read the comments of people who don't know me, never see me and are not inside me, telling me what and how I should setup my bike. You guys should make kids so that you can teach them all your knowledge... They'll worship you

    Have you ever heard of a guy named RYAN TREBON. Believe me, my situation is ten times better than him
    except Ryan is lucky enough to have custom FSA seat posts. He runs more drop on his mtb than most pros run on their time trial bike, wow. really is pretty oddly proportioned. The townie bike I built for him has a head tube that's almost a foot long

    don't bother listing to unsolicited fit advice, the internet breads experts and idiots faster than anyone can imagine. Although your solution is unorthodox to say the least I think it's pretty sound considering you almost have enough seat post in the frame without your extension, your just buying your self a little insurance.

  25. #25
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    27mm difference in the wheelbase between Med & Large and therefore the wheelbase is 'too long' and the handling 'awful'? Ah - OK - right - I see.

    I'm always amazed how people find ways to ride (too) small frames.

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