1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
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2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    Cutting Seat Post - Do I Cut Top or Bottom?

    Hi guys,

    I have 30" inseam and bought the smallest bike possible, but the seat post is still too high for me even when adjusted all the way to the bottom of the seat tube. I can reach the pedals with the tip of my foot, not the heel, so I'm barely reaching. This causes my pelvis to be very painful after each ride ... Therefore I'd like to cut my seat post.

    My question is, do I cut the top or the bottom of the seat post? I'd think that cutting from the bottom makes more sense, and then marking a new minimum insertion height line.

    Also, anyone brought their seat post to home depot for them to cut? How'd that come out?

  2. #2
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    obvious troll is obvious

  3. #3
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    Quote Originally Posted by BobaX View Post
    Hi guys,

    I have 30" inseam and bought the smallest bike possible, but the seat post is still too high for me even when adjusted all the way to the bottom of the seat tube. I can reach the pedals with the tip of my foot, not the heel, so I'm barely reaching. This causes my pelvis to be very painful after each ride ... Therefore I'd like to cut my seat post.

    My question is, do I cut the top or the bottom of the seat post? I'd think that cutting from the bottom makes more sense, and then marking a new minimum insertion height line.

    Also, anyone brought their seat post to home depot for them to cut? How'd that come out?
    We don't mind stupid questions but in this case please ask yourself the question you posted before posting. If you cut from the top of the seatpost, you would lose the ability to attach the saddle to the post.

  4. #4
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    Quote Originally Posted by mimi1885 View Post
    We don't mind stupid questions but in this case please ask yourself the question you posted before posting. If you cut from the top of the seatpost, you would lose the ability to attach the saddle to the post.
    Well put, the OP either doesn't have a clue or is a troll.

    Cut from the bottom with a hacksaw or dremel if you want to be able to use the seat.

  5. #5
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    This is a serious question; I searched before asking. I ask top or bottom because there were other threads (Google search) where they talked about top/bottom, and some suggested top for some strange reason that may apply only to that op's specific application/objective. I was sure it's the bottom, but just wanted to confirm before I make the cut...

  6. #6
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    Do as you have thought which is to measure and mark the minimum insertion line and then cut the post. HD might not cut it for you... Just use a hacksaw and a new/quality blade.

  7. #7
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    Well now you know

  8. #8
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    Bobax, there are seatposts that are just a simple post and have a cheap steel clamp assembly that gets slipped over the top. I sort of doubt that you have one of those, but anything is possible. Even then, the post is stepped down in diameter at the top end so that this said clamp can slip onto it. So, regardless of what you have, you always want to cut the post at the bottom. Always, Always, Always .

    I know that in another thread, you were asking for help with your Elixir 3's. Do you mind letting us know what kind of bike you've got etc., any changes you've made to it, so that we have a better idea as to answer your questions?
    Stay aware of those who hide in plain sight.

  9. #9
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    I have a 31.5" inseam, don't ride the smallest (or even second-smallest) adult bike, and show some seat post. And I have no problem reaching my pedal with my heel.

    I feel like there must be something else going on here. Can you post a picture of the bike?
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  10. #10
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    I just found by happenstance that he is riding a Motobecane Fantom. Apparently, after looking at a picture of that particular model bike, the seat tube has a kind of a bend to it where the suspension linkage ties into it. So, he really isn't able to put very much post into the frame.
    Stay aware of those who hide in plain sight.

  11. #11
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    Bobax, just make sure that when you do cut it, that you leave enough that you will still have atleast the minimum insertion length in the frame. This will avoid wrecking your frame and seatpost (most importantly your frame).
    Stay aware of those who hide in plain sight.

  12. #12
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    Cutting Seat Post - Do I Cut Top or Bottom?

    Quote Originally Posted by jochribs View Post
    I just found by happenstance that he is riding a Motobecane Fantom. Apparently, after looking at a picture of that particular model bike, the seat tube has a kind of a bend to it where the suspension linkage ties into it. So, he really isn't able to put very much post into the frame.
    If that's the case, then that answers a question I had: "if the seat tube is all the way down, why cut it at all?" If the bike is a poor design, and doesn't fit properly, send it back and get one that will fit him

  13. #13
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    I always cut mine in the middle that way it is reversible...
    When you've seen someone rupture their scrotum on a bike you won't take the standards for top tube clearance lightly!

  14. #14
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    You must have one of the DS model Motobecanes then. Yeah, just cut however much you need to off of the bottom of the post. I see 16" being listed as the smallest frame size available, and probably a big sized 16" at that. This was sometimes an issue on the old Trek Y bikes too.
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  15. #15
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    You know the rule...."cut from the top and ask questions later".

  16. #16
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    Dude.. you have a serious amount of issues with this bike .. front brake bleed, bent rotor, chain rub, seat tube, front fork..

  17. #17
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    Quote Originally Posted by emoe View Post
    Dude.. you have a serious amount of issues with this bike .. front brake bleed, bent rotor, chain rub, seat tube, front fork..
    It's a BD bike. I'm not surprised.

    But I'm not going to give the OP any crap about asking the question. Some carbon (road, mostly) seatposts are intended to be cut from the top. The seat clamp portion clamps onto the carbon post, and at some point lower on the post, the carbon is shaped to a semi-aero shape. There's a very small amount of adjustment on these posts (I think about 15-20mm) above the minimum insertion mark, and then the post narrows to a round shape near the seat clamp. So after the bike is fit and you know how high the saddle needs to be, you cut x mm from the top.

    But after reading, this is not the OP's problem. It's just the frame design. It's not surprising that a small frame with a bend in the seat tube is going to limit seatpost insertion. If the bike has a straight seat post, it's frequently the water bottle cage bosses that limit insertion. In these cases, you have two options: Cut the seat post (from the bottom), or buy a shorter post to preserve the minimum insertion mark.

    But I agree with AndrwSwitch, there's something else going on with fit. Looking up the sizing suggestions on BD's site, I think the OP just has a bike that's too big. This is the biggest problem with BD's bikes. Not enough sizing range.

    Looking here, Shimano DynaSys, 3x10 Speed 29er Full Suspension Mountain Bikes - MTB - 2011 Motobecane Fantom 29er | Shimano DynaSys full suspension mountain bikes | Save up to 60% off list prices on new bicycles, I suspect based on the information given in this thread and at the following link, that the OP is short...maybe 5'4 or so? I think it's stupid to say a small/16" frame is for someone in the 5'7-5'9 range. That would be me, and I ride an 18"/med frame, and sometimes think a 19" would fit well with a short stem. Ignoring for the moment that the sizing suggestions seem completely screwed up, BD seems to think it's A-Okay to screw over short riders (short guys and short to average ladies).

    I hate to be the guy telling people that they made a bad decision on a bike, but it sounds to me like the OP bought a bike that might be too small. That depends how much seatpost is still sticking out of the frame (how much lower can it go?) and how long the OP's torso/arms are. Maybe the bike works just fine for cockpit length and maybe there are several inches of seatpost length sticking out such that cutting off a couple would get the saddle height to an acceptable level.

    But it's also possible not. Bike manufacturers normally aren't in the business of installing obscenely long seatposts onto a frame so that a bunch of riders who buy the bike have to cut the post or insert it as far as it'll go (except maybe kids' bikes). Too much seat post means for higher material costs, which doesn't make sense when you're buying something that cuts just about every corner possible to lower cost.

    Pictures would help, of course. And not just of the bike, but also of the OP sitting on the bike.

  18. #18
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    Quote Originally Posted by emoe View Post
    Dude.. you have a serious amount of issues with this bike .. front brake bleed, bent rotor, chain rub, seat tube, front fork..
    First bike, first time assembling, adjusting, etc.
    Problem = an opportunity to learn.

    Quote Originally Posted by NateHawk View Post
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    Thanks for the thorough explanation Nate. I bought a small Fantom (link here). I'm actually barely 5'8 with 30" inseam. I'm not below average in height, but not THAT short that even the small Fantom won't fit me ... I will do a fit test after cutting the seatpost to see my reach, etc.

    Btw, the seatpost on that bike is 400mm regardless of frame size. If a large frame uses 400mm, it doesn't make sense for small frame to also use 400mm. I believe this is where my problem lies.

  19. #19
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    Cutting Seat Post - Do I Cut Top or Bottom?

    Okay, if those are your dimensions, your torso "should" fit the frame (if the fit guidelines are accurate), then you should be able to just cut the post and make things work. I guess BD cuts corners by including stupid long seatposts, too.

    Cut away. Just do a little at a time so you don't go too short.

  20. #20
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    Park Tool publishes a checklist, with links, for building new bikes. OP, I think if you go through it, you'll get out ahead of whatever the next problems with your bike are. You probably won't have to do everything. But at least make sure it's been done.
    http://www.parktool.com/blog/repair-...-bike-assembly
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  21. #21
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    Pictures always help. There are some posts that explain how to do that. Here's one: help posting pics There are others if this doesn't cover it. It's often hard for us to visualize what people are talking about. It sounds as though you are limited in how much of your seat post you can slide down into the frame of your bike, but it would help to see if that's the case.

  22. #22
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    As often happens around here, your post has gone off the rails a bit.

    It's no uncommon to need to cut a post on a full suspension bike. I needed to cut the post on my Yeti so I could put the post down low for technical sections. Hit it with a hacksaw and clean up the burrs with a file or some sandpaper. Grease it back up and put it together.

    Make sure you keep enough post in your frame or you risk breaking your frame. It was said above but bears repeating. There's a "MIN INSERT" line on your current seatpost, measure from that line to the current bottom of the post. After you cut, keep at least that much post in your frame at all times, I would recommend making a scribe line (if the post is black) or a marker line (for sliver posts) that indicates where your new min insert line is. If you've already cut, make sure you have enough post in the frame to get down below the weld for the intersection of your top tube and the seat tube. If this doesn't make sense, go to a bike shop.
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