shuru421

My bike originally came with a Sugino Spk which i researched to find out its 27.2, however when i bought my bike i removed the seatpost to find a 26.8 seatpost. And it seems pretty snug i might add, when i tried to put it back on.

CV-6 

It sounds like the slot on the back side of the seat tube is pinched together. Got a photo you can share?

The Golden Boy 

You know I have a bike that has a marked 27.2 that moves freely, I can't get any other 27.2 to fit. OK, that's 2 others, and I didn't do much playing 'cuz I didn't feel like scratching the posts.

mstateglfr 

You should use the seatpost size the tubing was made to use. If a 27.2 doesnt fit, take a thick flathead screwdriver or thin file and slowly pry the seat tube slit apart so it is evenly spaced.

It may be too loose and slightly oblong when you drop the 27.2 seatpost in, but thats fine as the top of the seat tube is malleable and will form around the seatpost once properly tightened.

plonz 

Using my digital calipers, I often find .2mm in variance betweem my measurement and the stamping on the post itself. Some are right on while others are off. Same goes with handlebar clamp areas vs. stated dimension.

I try to use the designated size but ultimately go with what feels best.

randyjawa 

By going too small with a seat post, you are running the risk of damaging the seat tube lug. The smaller post will allow the ears of the lug to close up, sometimes. And, the smaller diameter seat post will allow the seat lug cavity to distort. This is a pretty easy fix, but a fix that should be implemented so that the proper post will fit. This is How I Prepare a Seat Lug that has experienced problems...

RiddleOfSteel

Everyone is all over this, but my initial reaction at the headline was 'nope!' because I've tried and it didn't work even though I wanted it to... I'd vote to see if the slot looks pinched/tapered, to use a screw driver (remove binding bolts) to get the slot straight and try a 27.2 post and go from there.

79pmooney

Both seatpost ODs and seattube IDs can deviate from spec. Yes, your seat lug may be pinched but the tubing could also be a little off as can the seatpost.

I am surprised no one here has suggested shimming the post. Sheet aluminum makes excellent shims. I have my Mooney's MTB 26.8 post shimmed for the 27.2 tube. (In 1995 2-bolt seatposts were not in style. I wanted one. I saw two SunTour 2-bolt posts at a shop, a beautiful 27.2 road and an MTB post at half the price, same post but less fancy finish. I bought it and have been shimming it with Coke can shims ever since. My math says the shims should be too small and a loose fit, but the fit is so good it could pass for as designed so I haven't bothered to change it.

Ben

79pmooney

+1 (Basing decisions on reality? What a concept!)

Ben

SteelCharlie

It's been my unfortunate experience that new framesets are seemingly prep'ed by persons of dubious parentage and doubtful abilities. Not surprising considering the number of children that are employed by local shop kinda places. The Caylor that I have was done by a moron devoid of skill or knowledge in the use of what I can only assume was an adjustable reamer. Well, that's a lie. I know it was an adjustable cuz I saw it in the shop where I know the original owner had the frame prep'ed. And big buck shop that it was the "mechanic", and I use that term only as an identifier of position not skill, was clearly a defective and incompetent.

At the other end of that is the situation like one I had where the frame had been not prep'ed at all, just crammed together with no machining done whatsoever. Proved to be an unexpected challenge to dis-assemble. Not to mention problematic to find someone capable of attending to the necessaries.

At any rate, soft drink cans are a simple solution to a problem that often prompts homicidal urges.

but that might just be me


Charlie

shuru421

Done, Im going to go ahead and fine myself a sugino spk and have the bike as close to original components as possible. Just a wheelset/saddle away from that.

T-Mar

What is the tubeset? If it's one of the Tange Champion sets, 26.8mm may well be the correct size post?

shuru421

^ funny how you keep saving my life.

VINTAGE SUGINO SP-K 26.8 MM DIAMETER ALUMINUM SEATPOST/GREAT CONDITION!/JAPAN | eBay

This shows that the Sugino SPK in fact DID come in a 26.8 diameter. I just only happened to come across the the more common 27.2 diameter ones on ebay.

My frames tubing decal that DOES NOT say "Champion" on it, rather it says, "Chromoly Double Butted" in a red/green albeit being a Champion tubeset. Ive always wondered why/when they decided to replace it? I personally think the gold "Champion" decal for the tubeset compliments it better.

So possibly the "Champions" decals might be the 27.2 seatpost and mines actually is a 26.8?

Prowler 

This year's winter project is a 531 frame that came with a 26.6 seat post. Post was free and actually felt too free. The slot was pinched a bit. I borrowed a steel 26.8 post (yup checked it, 26.8 on the nose) and sure enough it fit beautifully after I opened the slot a whisker and wiggled the post in. Based on this thread, I cut apart a Coke can (I know it does not matter which brand but that's what I had) and measured the wall thickness = 0.1mm. Ah, beauty! I cut a test shim that covered about 3/4 of the post circumference and slid them both into the seat lug. Perfect fit. Before I'm done I'll cut a final shim and trim it to match the contour of the seat lug then tighten it all up. Easy peasy.

Loose Chain

You can buy steel or brass shim stock from .001 up. J

RiddleOfSteel

Forgot to think of shimming! As I sit three feet from one of my bikes which has its seat post shimmed... A while ago I had ultimately misread a 26.4 post as 25.4 and ordered a lovely seatpost from VO (not a VO seatpost, though). Don't know why I didn't bother with calipers which were somewhere lost at my place, but after swearing that I looked for the '6' and couldn't find it, I ordered it 1mm smaller. Pretty much been shimming it every since depending on the bike. Can't let it go to waste!