Fitting a 31.6mm dropped post to 31.8mm

Danieljephcott
Danieljephcott Posts: 334
edited August 2016 in MTB workshop & tech
Hello all,

I'm looking at getting a second hand dropper st some point but most come in a 31.6mm size.

I believe that my voodoo hoodoo has a 31.8mm hole and I was wondering if this will fit ok? To me it's only 0.2 mm but normally these things matter. Also being very heavy it's even more important that it tightens properly.

Would I just need some of the carbon paste and that's it?

Thanks in advance

Comments

  • friborg
    friborg Posts: 2
    Are you sure it is 31,8 inside diameter?
    31,8 sounds like outside diameter for a 27,2 inner diameter
  • Danieljephcott
    Danieljephcott Posts: 334
    Hmmm maybe. I measured the seat post and it's so hard to determine between a 0.2mm difference.

    My tape measures not the best.
  • Danieljephcott
    Danieljephcott Posts: 334
    Also I could do with some help on the sizing. I'm 5ft 11. I've measured my seat post from every frame to the top of the post just under the seat and it's 140mm. I've taken the seat post out and it's 390mm. So I'm thinking if I get a reverb I will need the 380mm x 125mm drop.

    Does that sound about right?
  • The Rookie
    The Rookie Posts: 27,812
    Most Merida made frames are 31.6mm, the seatpost will have it stamped in it and I'm pretty sure you will have the ubiquitous single bolt 31.6mm post.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Danieljephcott
    Danieljephcott Posts: 334
    Yep pretty sure it's a 31.6. Just need to work out which size to get. I'm actually thinking I need the 380mm x 100mm drop which is a shame. I think as there is a collar to contend with aswell which is about 30mm. Meaning the minimum the seat post will stick out the frame will be 155mm if I get the 125mm drop which will be to high. If I get he 100mm then the minimum amount sticking out the frame is 130mm which means I'll need to add another 10mm to give me my perfect seat hieght.
  • rockmonkeysc
    rockmonkeysc Posts: 14,774
    It is 31.6mm which is an odd size. You might get away with a 31.8mm post. Or you might need a 30.9mm and a shim..
    Transition Patrol - viewtopic.php?f=10017&t=13070235
  • whyamihere
    whyamihere Posts: 7,700
    31.6 is one of the 2 common sizes for droppers. I've never seen a 31.8.
  • Danieljephcott
    Danieljephcott Posts: 334
    Due to having a big frame and a low ish seating hieght at only 140mm I've had to go for the 355mm reverb with a 100mm drop. I'm pretty sure it's the only one I could of had. If I went for a 125mm drop then once you add on the coupler it's like 155mm which would have been to high.

    Anyway reverb is on order :)
  • The Rookie
    The Rookie Posts: 27,812
    RockmonkeySC wrote:
    It is 31.6mm which is an odd size. You might get away with a 31.8mm post. Or you might need a 30.9mm and a shim..
    Back to front, 31.6 is very common, 31.8 is rare. Probably why RS do a 31.6 Reverb (you can shim a 30.9 to fit a 31.8 anyway).
    http://www.chainreactioncycles.com/rock ... -prod84857

    That said my '31.6' Planet X frame is actually a 31.8, but as I was planning on using a shim with a 27.2 carbon post it wasn't an issue.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.

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