Bicycle Mechanics - 26.4 seatpost in a 26.6 tube?

So Wednesday I went to the local bike shop to get some parts measured so see what kind of parts I would need. The seat tube diameter is 26.6mm, would I be able to use a 24.4mm seat post?

nope.

Not recommended. Shims aren't so good either. universalcycles, cambria,jenson and others have most types. e-bay might if you would trust that.

If you're in a crunch, yes it will work.

Caveats:
1. You will have to shim.
2. You will also have to tighten the seatpost bolt more than usual.

It's not the best idea but ...

If you already bought the 26.4 seatpost and have a 26.6 seat tube,
You can use a piece of cardboard (yes paper) to shim it.
It's not the best, but it will work.

However if you're going to be using this long term (which i suspect)
and you haven't gotten a seat post yet, then get yourself the correct sized seat post.
That will put your mind and conscience to rest.

Damn... thats kinda gay. Is .2mm really that much?

yes, 0.2mm is really that much.

you have to think of it in circumference terms.

26.4mm has 82.86mm circumference
26.6mm has 83.52mm circumference

try inserting the 26.4mm into the frame, it'll fall right into the tube.
a perfect match will not.

get a can of coke

drink it

then get some sissors and cut it open
use the sides of the can to shim ur post.

i am doing this now with a campy 26.8 in a 27.2 and its not going anywhere.

you will only need 1 layer around the post. each layer is 0.1mm

So Wednesday I went to the local bike shop to get some parts measured so see what kind of parts I would need. The seat tube diameter is 26.6mm, would I be able to use a 24.4mm seat post?


The sizes you list in the text don't match the sizes you list in the subject. No way a 24.4 mm seatpost would work.

A 26.4 post probably would work in a 26.6 seat tube - 0.2mm differences are pretty common in stem/bar clamp diameters (25.8 bars in a 26.0 clamp)... depends on your seat clamp and maybe frame material, if you've got one lying around it might be worth trying it but I wouldn't buy the wrong size on purpose.

get a can of coke

drink it

then get some sissors and cut it open
use the sides of the can to shim ur post.

i am doing this now with a campy 26.8 in a 27.2 and its not going anywhere.

you will only need 1 layer around the post. each layer is 0.1mm

wow i think im gonna do this... good idea man thanks

Yes, it can be done. No, it shouldn't be done. They don't make seatposts in 0.2 mm increments just for the love of more stock numbers.

copy paper is right about .1mm (100 microns) thick. Just put one layer around your seatpost and slip it in there. I have to imagine a coke can is WAY too thick. I would imagine a coke can would be .2-.3mm thick, twice what you want.

I work with optics, we use paper as feeler gauges, so I am not just making it up. Standard copy paper, or even a post it note are right at .1mm, I measured copy paper just yesterday ;)

I would still buy the correct size soon, but you should get away with that. Only put it where the clamping area is, as that is the only part of the tube that squeezes the seatpost. If it gets wet, replace, and check it every day before ya ride. Paper is cheap...but still, get the proper size.

Just because it says "26.6 mm" on the tube does not mean that it is actually 26.6 mm in diameter. There is some variance in the seat post diameter and there is some leeway. If there wasn't any then seat posts would start slipping as soon as there was any wear at all on them, which doesn't happen with any regularity. The real issue is that a 26.4 mm post is really 26.3-26.2 mm in diameter, so it comes in a more than 0.2 mm narrower than the nominal diameter would imply.

.2mm kind of gay?
well there is a need to have accutate fit with stems , seatposts , handlebars.
if you have to you can get a 26.8mm post and EVENLY sand off a few thousandths of an inch to get it to 26.6mm, just mark the range of the post going inside the frame.
an undersize post can wreck a frame.

I would recommend you get some copy paper. But go and get some calipers too and then measure the copy paper. You might want to look into laminating the paper, but ask the guy for the "thin" lamination. He'll know what you mean. Once you get it back, come home and look at it for a bit, then measure it again with the new calipers. You probably should get the calipers calibrated and certified before you do this. Next, go out and buy a paper slicer. Cut the shim to a rectangle measuring 50.8mm X 82.8mm and then drink a Coke. You're getting close now so you could probably get away with a splash of rum in that Coke. wrap the shim around the seatpost with the 50.8 mm edge running longitudinally and the gap at the rear of the post, parallel to the axis of the seatpost, and then grease the seatube. You should research what kind of grease to use with a laminated copy paper shim first, as I'm not a lubrication engineer so can't say for sure. Ask the guy at the copy shop specifically what plastic the lamination is made of. He'll know what you mean. Insert the Seatpost and shim combination into the pre-greased seatube and then tighten the binder bolt. You'll need a torque wrench for this.Next, get on the bike and ride it to the LBS and ask them for a 26.6 seatpost. It'll be under 10 bucks.

copy paper is right about .1mm (100 microns) thick. Just put one layer around your seatpost and slip it in there. I have to imagine a coke can is WAY too thick. I would imagine a coke can would be .2-.3mm thick, twice what you want.



actually a coke can is about 0.09 mm wall thickness, it's just about right. People always think cans are thicker for some reason.

Shim stock: http://shop.ebay.com/i.html?_nkw=shim+stock&_armrs=1&_from=&_ipg=

How did this thread resurface? The last posting before these two new ones was 8 months ago.