Alloy mtb frame modification, seat tube and brace trim

  • This topic has 48 replies, 24 voices, and was last updated 2 years ago by  alexh.
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  • Alloy mtb frame modification, seat tube and brace trim
  • alexh
    Member

    I built the frame up as a winter bike, but I’m quite smitten by it and it’s geometry.

    The problem is the seat post is a bit long. I’ve trimmed it as much as I can in order to still fit a clamp above the brace.

    Ideally I would like at least another inch off it. I’ve already compensated a bit by using a super slim saddle and thicker than normal pedals.

    I know another owner has removed the brace entirely, in order to trim his seat tube without him or the bike imploding.

    Any recommendations on who could maybe take this on?

    Picture:

    View post on imgur.com

    Premier Icon lesgrandepotato
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    You could put the post down a bit?

    shorter cranks would be a better idea. That saddle isn’t super slim either.

    As for cutting the frame, do it yourself.

    alexh
    Member

    It’s a dropper post, it won’t go any lower.

    Agreed, that seat isn’t the slimmest. I’ve taken the specialized phenom off as its an instrument of pain. It’s got my 170mm cranks on it too.

    As for cutting it myself, it’s something I’m considering. Grind down the welds to the brace and then send it away to be refinished?

    Premier Icon letmetalktomark
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    Why not run it slightly “dropped”?

    It’s a dropper post, it won’t go any lower.

    Agreed, that seat isn’t the slimmest. I’ve taken the specialized phenom off as its an instrument of pain. It’s got my 170mm cranks on it too.

    As for cutting it myself, it’s something I’m considering. Grind down the welds to the brace and then send it away to be refinished?

    Selle SLR or a Pro Turnix a pretty slim saddles. 165mm cranks are another option (and seem popular these days). Or get some thicker socks!

    As for cutting it myself, it’s something I’m considering. Grind down the welds to the brace and then send it away to be refinished?

    I don’t think it’d be too much trauma to cut the brace off. Then just file the welded areas flush. It looks like it’s anodized? I’d probably just put some toiuch up paint on it and leave it at that.

    Premier Icon mechanicaldope
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    Shorter drop dropper? I’ve always wondered how small a persons frame must be if they can run a 170mm dropper.

    Premier Icon TomB
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    Pic didn’t show for me, I have tried to put it up here :

    mikewsmith
    Member

    Doesn’t look like much to cut off, the brace is there for a reason…

    alexh
    Member

    The other issue is that even when the seat is dropped, I don’t feel it’s giving me enough room to move around. It’s too high compared to my other bikes.

    I agree, the brace is there to support a moment on the long seat tube, but if the tube is sufficiently trimmed it should not need to be there as its braced by the top tube.

    David, it is ano finish. I’m more minded to DIY it. I might do some measuring and planning. I’ll lose the end of the decals on the post, but as its really a winter hack, I’m fine with that.

    legend
    Member

    I agree, the brace is there to support a moment on the long seat tube, but if the tube is sufficiently trimmed it should not need to be there as its braced by the top tube.

    But the top tube likely hasn’t been designed to handle the load on its own

    Premier Icon russyh
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    Can’t you go for one of the droppers with the shorter collars? Was it the Bikeyoke dropper that had a slim top collar?

    Premier Icon chakaping
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    I know exactly how you feel with it, most bikes I like the look of have seat tubes too big for my stubby legs.

    I have a leftfield suggestion for you, based on owning the same bike…
    http://unduro.co.uk/mtb/behold-the-frankenthumper-aka-project-279/

    If you favour technical trails over covering miles, there’s not much of a downside at all.

    IA
    Member

    I’ve always wondered how small a persons frame must be if they can run a 170mm dropper.

    My frame’s enormous, but you should see the length of my legs 😉

    Stevet1
    Member

    I’ve done something similar in the past and the one piece of advice I would give you is – make sure the seat tube is the same diameter all the way down…

    Just get a dropper with a 100mm instead of 125mm drop??

    thepodge
    Member

    I have essentially the same frame and before buying it considered a similar modification to get a longer front end but decided against it because…

    Seat tube could be slightly different internal dia.
    Grinding could cause heat problems in the alu frame.
    Toptube seat tube joint may not be strong enough.
    Seat could be so low the wheel gets in the way when post is dropped.
    You may not be able to insert the post much further because of the seatube bend.
    Didn’t want to generally fubar a perfectly good frame.

    philjunior
    Member

    1) You’ll weaken the frame (whether it breaks there as a result depends on a lot of things).
    2) When your suspension bottoms out it will hit the saddle if you lower it too much.

    I’d guess different frame/shorter dropper post/put up with it are your best options.

    Premier Icon Andy R
    Subscriber

    chakaping – Member
    I know exactly how you feel with it, most bikes I like the look of have seat tubes too big for my stubby legs.

    I have a leftfield suggestion for you, based on owning the same bike…
    http://unduro.co.uk/mtb/behold-the-frankenthumper-aka-project-279/

    If you favour technical trails over covering miles, there’s not much of a downside at all.

    But fitting a smaller rear wheel won’t change the saddle height, so the OP’s problem willstill be the same.

    How much too high is the saddle at present – or did I miss that?
    I wouldn’t even entertain the idea of removing that brace – simply because you’ll ruin a perfectly good frame and the seat tube will probably end up fracturing anyway.

    Premier Icon Andy R
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    Ok – I did miss it. Another inch off it.

    So, cut the seat tube as short as possible without cutting into the weld area – that should get you 20mm by the looks of it.
    Drill two 5mm holes in the back of the seat tube in the area between the top tube and the brace and then slot between them, say 2mm wide. Find, or get made up, a split clamp to suit the frame dia and clamp the seatpost with that.
    Unorthodox maybe, but it’s a better solution from an engineering point of view than removing the brace.

    Premier Icon superstu
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    Don’t do it. Keep it and make do or sell it and fund something that fits IMHO.

    Premier Icon nwmlarge
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    I had the same issue with a Lapierre spicy,

    I cut what I could off the seat tower and fitted a reverb which is the lowest clamp to rail height I could at the time.

    In the end I conceded and bought a Saracen Ariel and its a dream.

    I get a much lower seat height when it is down and feels like it is out of the way now when i’m throwing shapes.

    Premier Icon chakaping
    Subscriber

    But fitting a smaller rear wheel won’t change the saddle height, so the OP’s problem willstill be the same.

    It will drop the rear of the bike by 2cm, so the saddle and BB should be at least 1cm lower – combined with the slacker HA it will make the bike MUCH more confident on steep stuff, which I assume is where the OP is having trouble.

    As hes running a dropper, I dont think it’s an issue with the steep stuff, just his legs arnt long enough when the dropper is at full extension.

    Premier Icon chakaping
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    I see what you mean and I take the point about wheel size not changing distance from pedal to top of saddle, I was focusing on this bit…

    even when the seat is dropped, I don’t feel it’s giving me enough room to move around. It’s too high compared to my other bikes.

    I have a 150mm dropper that came on my enduro bike – and at full extension it’s 5 or 10mm too high. I’ve got very good at micro-dropping the saddle or stopping it at the right height with my bum.

    Premier Icon kayak23
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    Just get thick pedals innit… 😀

    alexh
    Member

    It’s a two-fold problem of my legs not quite being long enough to use a preferred saddle and pedal combination, and I’d like the seat a touch lower on the ‘gnarrrr’

    I’m minded to think if I were chopping the seat tube to near the top tube (25mm or so) I would not be concerned about losing the brace. However, I’m listening to the advise above and post dia and insert length (to the bend) need checking first.

    You may think I’m ignoring the other comments on the potential to snap the seat tube, but if it’s shortened enough, I can’t see it breaking as the moment on the welds from my seat load is dramatically reduced. I’m also 11st, and the frame cost me very little.

    I’ve taken the seat post tube down as much as I can, whilst still leaving enough room for a small clamp above the brace weld. I don’t quote follow what was mentioned about the split clamp and the holes.

    The 650 rear wheel might be an option, but I fear it will be a bit extreme and lose the roll over characteristics (it’s got a minus 2 degree headset and 140 fork already, and pedal strikes are easily instigated). I think I’ve read some of your blogs previously, chakaping. The wheel supplier you mention in your blog, was the owner I spoke with who removed his brace entirely (who purchased my canfield yelli frame too-small world)

    I’ve made do by using old v12 dmrs and a thin saddle, but I’m not enjoying that saddle, and the pedals don’t help with strikes either.

    Time for some more measuring before I crack open the tools.

    Premier Icon chakaping
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    The 650 rear wheel might be an option, but I fear it will be a bit extreme and lose the roll over characteristics

    It didn’t lose much (if any) rollover ability downhill, but on flat bumpy stuff it was noticeably harder work.

    it’s got a minus 2 degree headset and 140 fork already, and pedal strikes are easily instigated

    OK, you’ve talked me out of it!

    Have you thought about 165mm cranks? Zees are fairly cheap, if you’re single ringing it.

    Just a thought if you go ahead. Are three any bottle bolts on the steattube? These often protrude into the steattube and prevent dropping long (400mm) seatposts. If so they would need reaming out. It would be the same if there are any welded junctions further down the steattube that your current post doesn’t reach..

    alexh
    Member

    The zee cranks are flipping heavy though. I am going to try the yari fork with a 150 air spring. I have bottomed the fork on the local dh trails. This should remove my low bb /pedal issues.

    No cage bolts to worry about, just that bend by the mech mount.

    alexh
    Member

    Well, no going back now.

    I had the angle grinder out to fix the wife’s exhaust.

    So here it is

    View post on imgur.com

    I’ll update the post if it snaps.

    That looks spot on – well done!

    Premier Icon kneebiscuit
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    Will the saddle not catch the wheel when it’s dropped and you hit something big?!

    Premier Icon kneebiscuit
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    Ps fair play for having the cajones to just do it!

    Premier Icon superstu
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    Will the saddle not catch the wheel when it’s dropped and you hit something big?

    My thoughts too.

    I also wonder how that seat tube will get on. I’d keep an eye on it.

    The small Hammerhead Thumper frame is pretty much the same as the OP’s now so there shouldn’t be an issue with the rear wheel / saddle clearance.

    Easy to check by letting the air out of the shock.

    thepodge
    Member

    First dibs on the frame if / when it dies or you get rid. It’d be good to have spares for mine

    alexh
    Member

    Theporge, noted.

    Clearance is fine with a flat shock.

    Load path on big hits is up the stays and to the shock mount. I just need to be mindful how much I load the seat tube when seated.

    Most of my riding is up fire roads and then down trails.

    Time will tell if it survives.

    Premier Icon takisawa2
    Subscriber

    Couldn’t you have just modified the dropper stanchion, ie: remove the head, shorten & re-attach ? Its probably just pressed on.

    But fair play for a tidy job in taking the brace off.

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