Seatpost - is it a 26.2 or isn't it?

[Yog Sothoth]

Bought a NOS saracen frame, unbadged, so no idea what model. Pre-disc though. I measured the seat tube ID at 26.2mm using verniers, although it was very slightly over 26.2.

Anyway, ordered a 26.2 seatpost from America which has now arrived. Blow me if it doesn't just drop straight in, with slight play! I re-checked the tube size, and sure enough, 26.2 and a tiny bit over. Measured the post and it's 26.2 and a tiny tiny fraction under. Should this matter? Whatever, I can't believe it should account for the loose fit.

Makes me wonder if my verniers are out! :shock:

When I say there's play, I mean it actually rattles slightly. There's no friction as I drop it in. If I hadn't measured it, I'd swear it needs a 26.4, but I'm damned if I'm buying another post on a gamble.

Thing is, 26.2 to 26.4 is too thin for a shim. I have a spare 25.8 post but again, shims don't seem to be available for the conversion to 26.4 (after an online search).

I've no idea what post sizes Saracen used in their late 90s frames ( I'm guessing the age) so it's all getting a bit 'try it and see'. :?

 

[Charlieboy28]

might be some help might not, i had similar problem with a 27.6 tube and 27.2 seatpost which needed a shim, use do a 0.4 shim for 25-25.4 which they advised me to use, didnt work for me though, could not get the shim and seatpost in?

it might work for your 25.8 to shim to 26.2 though and maybe slightly bigger than 26.2 which is what you need

 

[Andy R]

Thing is, 26.2 to 26.4 is too thin for a shim.

Not in the world of Coke cans, it's not

.004" thick (0.1mm) so just perfect. Make it about 70mm long and leave about 2mm proud of the seat tube and roll a small lip onto it to stop it sliding too far down. It it all works and fits ok, then degrease the top 75mm of the seat tube (and the outside of the shim), mix up a bit of epoxy and apply to the seat tube, fit the shim and then the seat post and leave it while the adhesive cures. Trim the lip if it gets in the way of the seat clamp.

I've had one like that for a couple of years now on my '95 Explosif, which is nominally 27.0mm but too loose for a Thomson 27mm post. Works faultlessly.

 

[Yog Sothoth]

Thanks guys. I'd heard mention of coke cans on another forum so I think I'll try that. If that fails I'll gamble a few quid on a USE shim. Is that a plastic or alu shim btw? I know USE do both.

 

[Charlieboy28]

for that thickness its ally, and pretty much like a coke can

 

[Yog Sothoth]

Funny how post sizes and tube sizes don't always match, despite what it says on the tin!

I've always found it a bit puzzling that seatposts come in 0.2mm increments, from 25 to 30+mm, which is a far bigger size range than any other bike component, and which (as I'm finding) can be infuriating if you're starting with a bare frame.

Marking the seatpost size on the seat tube would be a helpful step for manufacturers to make.

 

[FMJ]

I measured the seat tube ID at 26.2mm using verniers, although it was very slightly over 26.2.

I can give 5 guys the same pair of verniers, have them all measure the same part, and get 5 different dimensions. That's why we jokingly refer to them as "very nears".

 

[Andy R]

I measured the seat tube ID at 26.2mm using verniers, although it was very slightly over 26.2.

I can give 5 guys the same pair of verniers, have them all measure the same part, and get 5 different dimensions. That's why we jokingly refer to them as "very nears".

They do to an extent rely on "feel", although not as much as ordinary inside calipers - as far as seat tubes go you can only measure the ID of the top 15-20mm with verniers anyway, which although it should be the same as lower down sometimes isn't as the top can get very slightly splayed (or pinched for that matter).

 

[mikee]

it's often best if your unsure to get someone to turn up a bung
with the nominal size ie 26.2 and .2mm either side to check for sure

digi- calipers cause endless hours of mirth at work as desk engineers
measure things to within 1/4 an inch , one bloke was 9mm out on an
actual dimension of 216mm

 

[Barneyballbags]

I've got the same problem with my build at the moment....

1996 LTS which is supposed to take a 27.0 seatpost. Tried to drop a 27.0 in there and it will only go in a small amount before it gets stuck. So I'm thinking that I might need a 26.8...

Also, my LBS measured up my Alpinestars Cro Mega for a seatpost and came up with 29.4mm. I dropped a 29.4 in and it's a fraction small. It still clamps up ok though.