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  1. #1
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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
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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
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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
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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
    http://oilcanracer.blogspot.com/

    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
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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
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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
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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.

  26. #26
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    i feel your pain, i have to ride a med niner air9 with a 410 thomson at the max with a 70mm stem. although i dont get bad handling issues. pretty much all my mtbs follow the same formula as well.

  27. #27
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    Quote Originally Posted by TooTallUK
    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.
    Exactly my thoughts too and with a remark like "I hope this might help someone"...well yah it might just help someone being seriously injured or even worse.With all the good parts out there im shure one can find a better soultion (as said bigger frame,shorter stem,sweepback bars,ect.).I have no issues with inovation but to what cost?

  28. #28
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    Quote Originally Posted by TooTallUK
    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.
    i would guess that it has more to do with the 40mm shorter stem and not being used to feeling so far behind the wheel instead of over it. That difference can definitely be noticeable and can make the wheelbase feel "longer". Combine that with an actual 27mm difference in wheelbase and you certainly have a difference in handling

  29. #29
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    Quote Originally Posted by Menzo
    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.
    Funny, you moan about the handling of a slightly longer bike, yet you run Furious Freds.

  30. #30
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    Quote Originally Posted by monolith
    Funny, you moan about the handling of a slightly longer bike, yet you run Furious Freds.
    yeah he is obviously only riding in straight lines since he doesn't have real tires. Once he puts on some nice big DH tires he can comment on the handling of his xc race bike

  31. #31
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    It's not only about the insertion, but the leverage. Way to void the frame warranty. I'm sure Spec is going to be scrutinizing over any of these they get back for failure.

  32. #32
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    Pics saved for later LOL usage.

  33. #33
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    i would guess that it has more to do with the 40mm shorter stem and not being used to feeling so far behind the wheel instead of over it. That difference can definitely be noticeable and can make the wheelbase feel "longer". Combine that with an actual 27mm difference in wheelbase and you certainly have a difference in handling
    Yep your are right

    I don't make any assumptions, unlike many comments here, I say assertions based on my experiences. I don't ride a medium just for the sake of riding a medium but because after I tried several sizes and several setup that is the one I feel good.

    Few numbers (for those who understand maths and logic) : The medium Epic has 590mm effective top tube vs 615mm for a large. The wheel base is 1109mm vs 1136. Both have the same seat tube angle 74 deg and chainstay length 448mm. Which mean going to a large extend the seat tube (ok that's good) BUT it also extend the front of the bike of a full inch. Those who say stupid things like "it makes no difference" are making assumptions. Back in the days when there was no sloping top tube geometry with freakin short seat tube I had no problem ;-)

    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.
    I think the pictures give the impression the seatpost is more extended than it is for real or maybe that it because my stem is at the lowest although the saddle and bars are almost even heiight. I don't really understand why people are raging... oops this comment will bring more rage
    Last edited by Menzo; 05-17-2010 at 01:59 AM.

  34. #34
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    I hear there are other bike manufacturers out there who have different geometry. That might just be a rumour. There will always be people totally dedicated to getting a certain bike to fit despite all evidence that another brand might be better for them.

  35. #35
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    I <3 confused mtbr bikes.

  36. #36
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    Quote Originally Posted by customfab
    except Ryan is lucky enough to have custom FSA seat posts.
    I think that's the route I would go if I needed a really long post. Custom usually allows you to go up to 500mm long. And for a weight weenie, I am assuming it would weigh less.

    Menzo - your bike looks sweet and fast. Nice work on the seatpost work around.

    BB

  37. #37
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    The only long seatpost available on the market is the Syntace P6 Carbon (480mm) but not in size 30.9. No custom builders where I live, I had to use my brain but the result is solid although there is a penalty of 70 grams because of the double layers.

  38. #38
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    You're on the wrong size bike.

    I hear that alot. 5'11" with over a 35in inseam. I feel the OPs pain. You should see the length of the head tube on my custom Lynskey road bike. The solution - custom Ti Rockstar. I'm more than willing to spend your money.

    The Serotta Tech with years of experience that fitted me told me he only had one other customer with such atypical proportions. Some people are just on the end of the bell curve.
    Last edited by DrDon; 05-17-2010 at 06:47 AM.

  39. #39
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    I think that JHK's seatpost is way too high and its frame undergoes too much leverage and might break...
    Attached Thumbnails Attached Thumbnails How to : Extend a 400mm seatpost-jhkscustomsf100.jpg  


  40. #40
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    It's funny how a group of people who actively encourage 5'2" rider to buy 29er also talk about how a rider using a 80mm stem on an XC bike needs the next size up. One size MUST fit all!!

    Nice looking bike. Good job making it work better for you.
    Each bicycle owned exponentially increases the probability that none is working correctly.

  41. #41
    The White Jeff W
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    Quote Originally Posted by laffeaux
    It's funny how a group of people who actively encourage 5'2" rider to buy 29er also talk about how a rider using a 80mm stem on an XC bike needs the next size up. One size MUST fit all!!

    Nice looking bike. Good job making it work better for you.
    ..and how the standard mantra around here is 'go to the lbs and buy the bike that feels best' but when this fella says the bigger bikes don't ride well for him he's doing it wrong.
    No moss...

  42. #42
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    Clever solution by the op. Part of the problem is the radical slope on the top tube. Other brands of medium bikes would probably fit him without so much seat post needed.

  43. #43
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    Quote Originally Posted by jeffw-13
    ..and how the standard mantra around here is 'go to the lbs and buy the bike that feels best' but when this fella says the bigger bikes don't ride well for him he's doing it wrong.
    my main problem with this is that i doubt the OP tested other bikes/sizes for long enough to get over the "it feels wrong because it's not what i'm used to".
    a parking lot ride definitely won't do it.

  44. #44
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    Quote Originally Posted by syl3
    my main problem with this is that i doubt the OP tested other bikes/sizes for long enough to get over the "it feels wrong because it's not what i'm used to".
    a parking lot ride definitely won't do it.
    Let me get this straight, you insult somebody based on an assumption that this person didn't buy a bike according to your standards without knowing anything (or not much) why this person purchased the bike under what circumstances?

  45. #45
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    Quote Originally Posted by Minimalist
    Let me get this straight, you insult somebody based on an assumption
    You call that an insult? Dry your eyes, princess and a hug will make it all better.

  46. #46
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    Quote Originally Posted by Minimalist
    Let me get this straight, you insult somebody based on an assumption that this person didn't buy a bike according to your standards without knowing anything (or not much) why this person purchased the bike under what circumstances?
    Welcome to the Internet!

  47. #47
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    Quote Originally Posted by sanjuro
    Welcome to the Internet!
    I know, but sometimes I wish that the dull tools would just shut up. Guess I am a dreamer.

  48. #48
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    Btw, based on the stem length and the assumption the rider does fit this bike correctly, I just wonder how the frame will hold up with a longer seatpost. Time will tell.

    Personally, I would save my pennies for a custom frame.

  49. #49
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    Looking back on the OP, he says that he "used this trick for a few years". So, whether you like it or not, it seems he has proven this as a reliable solution for himself.

    Being a short legged guy, I never have a whole lot of seatpost sticking out and it does look like there would be a lot of stress on it, but how much stress is too much? They make 400 mm seatposts, and that seems like a lot, but they work, so why can't 485? Apparently, it does work for the OP.

  50. #50
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    Going out on a limb here, but the OP also may well not be as fat as the average mtbr user, and it sure seems like leverage on the frame is also going to be determined by the weight on the seat, hm?

    While not as extreme, I have similar issues sometimes with fit (longish legs to torso) so I can understand the issue. I am a little bit taller though, and usually end up on large frames. Not always.

    But no matter, the mtbr types will just go on riding their rigid singlespeeds with weird looking handlebars and flat pedals around the upper midwest, complaints and criticisms drifting on the breeze.

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