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  1. #1
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    How common is cutting the seat tube on a new bike?

    I was checking out some bikes that were "fit for me" by the LBS, but the seat was too high, even after lowering them all the way. They said that they could cut the seat tube an inch or 2 so it would fit me. I did try the next smallest bike size, but that was much more cramped. So my question is how common is it to cut the seat tube? Do they always make it longer to accommodate taller people but allow it to be cut for shorter?

  2. #2
    Home School Valedictorian 02Giant's Avatar
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    I think they had two sizes, one too big, the other too small, and are trying to sell you one of them.
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    Senior Member brianmcg123's Avatar
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    It's very common. Some bikes come with excessively long seat posts. The bottle bosses get in the way if you try to put it down far enough.

    Let them cut it.
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    Seat tube NO. Seat post OK, but I agree that some sellers will try to sell a poorly fitting bike. And others may not know how to fit a bike.

  5. #5
    rugged individualist wphamilton's Avatar
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    He's talking seat tube, not post.

    Even if you did that, what about reach?

  6. #6
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    What he said, a seat tube you could cut a couple inches off of? I wouldn't think so, seat post yeah.

  7. #7
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    He said seat tube, but I'd guess he meant seatpost. Anyway, I'm with Al1943 & brianmcg123. Cutting the frame would be a MAJOR no-no, but if the bike fits otherwise, it's OK to trim the seatpost if need be.

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    Given the nature of the question, I'm fairly certain the OP means seat post, despite writing seat tube. For clarification the seat post is the part that slides up and down inside the seat tube of the bike frame.

    What bike models are you looking at? If its a sloping top tube design, I'd really question cutting the seat post. You can do it, but its usually because the bike doesn't really fit. Unless you have a very long torso, which would need a low seat and long top tube.

  9. #9
    Quirky Grifter LesterOfPuppets's Avatar
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    What bike make/model are you looking at? How much seat post is showing when it's bottomed out?

    On some frames a long seatpost can bottom out while a LOT of post is still showing.

    Are you trying for a feet flat on the ground while butt is in the saddle type of fit?
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  10. #10
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    I agree that it was most probably about a seat post not sliding past the bottle bosses.

    But there remains the small possibility that the OP is very short, and the shortest 26" bike is a bit tall, and going 24" too limiting. In that case, a skilled and knowledgeable shop might determine that 1" or so could be trimmed off the seat tube, and the slot extended accordingly. Many frames these days have seat tubes extending way beyond the top tube or seat stay joints, IMO unnecessarily so, and have room to trim. In fact we've seen a reasonable number of failures in this extended seat tube design.
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    Ok - I guess I meant the seat post as that is connected to the seat. I tested a Giant Roam in S, M and L. Both the L and M were too tall. The S was fine, but the length to the handlebars were cramped. The seat extended about 5 - 6 inches and couldn't go down any further.

    Sorry for the confusion. I'm still learning the bike parts.

  12. #12
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    Quote Originally Posted by lhrocker View Post
    Ok - I guess I meant the seat post as that is connected to the seat. I tested a Giant Roam in S, M and L. Both the L and M were too tall. The S was fine, but the length to the handlebars were cramped. The seat extended about 5 - 6 inches and couldn't go down any further.

    Sorry for the confusion. I'm still learning the bike parts.
    No sweat. Get the bike with the better overall fit, and as posted, there's no problem with cutting the post unless you suddenly have a growth spurt.
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  13. #13
    Senior Member Wilfred Laurier's Avatar
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    question for lhrocker

    were they talking about cutting the seat post
    which is the removable part that slides in and out
    or
    were they talking about the seat tube
    which is the part of the frame where the seat post goes

    the two answers to your question are
    if it is the seat post that would not go down far enough
    this is very common on smaller frames
    as they often come with the same long seatpost as larger frames
    and features inside the seat tube
    usually the water bottle bosses
    so cutting the seat post
    is not necessarily an indicatio of a poor fit

    if
    however
    the seatpost went all the way in
    and the saddle was sitting directly on top of the frame
    and the shop wants to cut the top of the frame off
    that sounds mvery much like a bike that is too small

    you say this is the smallest 26" wheel bike they had
    but it is not the smallest frame available
    so you may need to find a different shop
    and see what they have

  14. #14
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    Hey Will,

    I'm talking about the post that the seat is on that goes up and down on the bike. Fully inserted, there is about 6" of post sticking out. The wheels are 700c's as this is a Giant Roam. Being a beginning biker, I wanted the seat to come down a little lower so I can learn with confidence. Hope that helps. I also tried out a Giant Escape in Medium, and I was able to lower the seat significantly more than the Roam.

  15. #15
    coprolite fietsbob's Avatar
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    cramped reach to handlebars is cured with a longer stem, Ideally, swapped by the shop
    before you took the bike home.

    yes a frame with a greater slope to the top tube will allow a lower saddle drop .

    no matter what brand .. /model ..

    If a shop doesn't have your size when you walk in, you may have followed the sales of that one,
    they did have in stock, to someone, also your size ..
    and either have a boxed bike yet to be assembled or have to restock from the importer's distribution warehouse

    It's Summer .. that happens .. FWIW, repair turnarounds are faster in the winter..
    Last edited by fietsbob; 07-20-14 at 12:48 PM.

  16. #16
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    I work in a Trek shop. There's usually one size of one model each year where they spec too long a seatpost for the size and we end up having to cut posts for riders right on the border between that size and the next size down. Usually a mtn bike, one of the smaller sizes, like a 16" or 15.5" model. 90% of those buying the bike won't need it cut, but it won't fit that in-betweener without cutting the post. A customer or two each year. OP is one of those lucky customers.

    Since cutting the frame voids the warranty, I can't see a shop suggesting cutting the seattube... Not only that, but it would also not eliminate the issue with the too long seatpost...
    I know next to nothing. I am frequently wrong.

  17. #17
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    Quote Originally Posted by lhrocker View Post
    .... Being a beginning biker, I wanted the seat to come down a little lower so I can learn with confidence. .....
    Often, the only thing blocking the post is the waterbottle screw extending into the frame. In these cases, simply removing the screw solves the problem, allowing the post to go past. I'd buy the bike that was the best overall fit and see if removing the screw solves the problem. Otherwise cut the minimum needed to achieve your goal off the post, hopefully leaving enough for you to get ideal saddle height next month.

    Worst case, you cut too much off and have to shell out for a long post later.
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  18. #18
    coprolite fietsbob's Avatar
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    seat post diameter is right, Product management, the main criteria in choosing the part is price..

    and is often shipped with the saddle on it in the box, 1st time its inserted is dealer assembly..

    seems 29ers the post bottoms out on a bend in the seat tube , bent to get tire clearance in the front.
    without making the chainstays longer, affecting the climbing traction..

    sawing of a bit off the bottom of a seat post that only retails for $25 is no big deal ..

    back when the convention was a horizontal top tube and typical stand overs were high.

    .. the seat posts were Made shorter .. things change ..

  19. #19
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    Small, medium, large is not enough sizes to fit all riders. I suggest you shop brands that have more sizes.
    And there is a lot more to fitting a bike than just the height, like top tube length and knee over bottom bracket relationship.
    Last edited by Al1943; 07-20-14 at 01:39 PM.

  20. #20
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    If you like the reach of the bike from the seat to the handlebars, but the seat is too high, then definitely cut the post. I have my bike fitted similarly. I like a long top tube, so my bike is technically too big for me according to all the smartypants cyclists out there. But, with this set up, I can blow through a Century with absolutely no discomfort.

  21. #21
    自転車整備士 oldskoolwrench's Avatar
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    There are times that a seat post needs to be trimmed, as fietsbob and mconlonx have said. I've done it many times in order to get the seat lower on a 24" kids MTB, or in order to fit myself better.

    The important thing is to make sure you have enough inside the frame; I like to use a minimum of 4.5" inside the seat tube as the general rule, dependent on the seat cluster type.

    Like fietsbob said... not much worry when it's an inexpensive OEM post. A Thompson Elite, well... I wouldn't recommend it, but I have done it before, for one of my bikes.

  22. #22
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    Quote Originally Posted by oldskoolwrench View Post

    ... not much worry when it's an inexpensive OEM post. A Thompson Elite, well... I wouldn't recommend it, but I have done it before, for one of my bikes.
    No reason not to cut ANY post as long as you understand the question of minimum insertion. Even a Thompson, which is unique because the company allows this modification without voiding the warranty. As they point out, cutting a post shorter also makes it stronger.
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  23. #23
    自転車整備士 oldskoolwrench's Avatar
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    Quote Originally Posted by FBinNY View Post
    No reason not to cut ANY post as long as you understand the question of minimum insertion. Even a Thompson, which is unique because the company allows this modification without voiding the warranty. As they point out, cutting a post shorter also makes it stronger.
    I wasn't aware of that, FB! Many thanks for the info!

  24. #24
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    Quote Originally Posted by brianmcg123 View Post
    It's very common. Some bikes come with excessively long seat posts. The bottle bosses get in the way if you try to put it down far enough.

    Let them cut it.
    Yea, it's not a big deal to cut it, as long as the bike really fits properly.

    My wife had that problem with a bike that otherwise fit her fine - the seat post was a full-length type (at least 350 mm) and wouldn't lower enough because of the water bottle boss. Cutting it was dead simple and quick. We had the shop do it (it was a rental), but I could have done it in 2 minutes with a hack saw. The cut doesn't even have to be perfectly straight. Make sure they re-mark the "minimum insertion" line based on the new length though.

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