onespeedbiker

I bought this Schwinn Peleton new in 1999. Since then I changed all the Shimano Components to Campy and the seatpost/stem to Nitto. What I noticed however is the spec'd 27.0 seatpost started to slip; perhaps it was the difference between the beadblasted OEM Titec and the polished Nitto, but I suspected something else was amiss as the seatpost seemed to wallow a bit in the seattube and it seemed to take more turns than usual to tighten the seatpost collar. So, I removed the seatpost and tried a 27.2 and it fit perfect! I then did a search and it turns out few 853 Peleton owners had experienced the same issue. Is this just a matter of variable tolerances, is this common or is this unusual?

fietsbob

It is not a hand crafted frame , it came out of a factory.
not all 27.0 seat posts are 27.000 precise.
ditto 27.2 being 27.200.

onespeedbiker

I mic'd them both and they were right on..The seat tube at the collar was a bit ovalized still I got 27.0 side to side and 27.3 front to back. There is little doubt this seat tube should have been spec'd for a larger seatpost..

Jeff Wills

No, they're never that precise, unless you're talking a high-end frame that's been prepped properly at delivery. The next larger seatpost would be 27.2mm diameter, which I guarantee will jam in the seat tube if you try to insert it.

You could try taking the frame to a good shop that has the correct reamer and the knowledge of how to use it. Other than that, a beer can shim would help.

fietsbob

+1, get the tube ID de-ovaled, then, the fit for the post improved, as above.

FBinNY 

Seat tube tolerances are usually pretty close. It has nothing to do with the frame being high quality or hand made. The tubing is supplied at the right size from the mill, and these guys know how to hold a spec. Some factories pass a reamer (fixed size and will cut to spec,) down the tube as a final operation to deburr the slot, and correct any minor ovalizing.

Then best test for seat post fit is to look at the seat tube slot when the post is clamped. The slot is milled into the finished frame and the sides start out parallel. A properly fitted post will have a close running fit within the tube, so when clamped the top of the slot will close only slightly. If it closes to less than half the original width there's a good chance the post is too small.

As to why these particular bikes have a problem, I can think of three likely reasons.
1- an undocumented change in the tube spec., and so a mismatch between the posts brought to the assembly line and the frames.
2- a simple typo in the working spec sheets, so wrong posts were purchased.
3- a dealer who reamed the seat tube bringing the ID above the original spec.

The why doesn't matter. The largest post that fits into the tubing below the lug or weld area (4" down) is the correct post.

onespeedbiker

Perhaps you missed my original post. I inserted a 27.2 seat post and it slid (in about 200mm) like the two were made for each other. BTW, I'm a bit anal when it comes to proper operation and fit. The idea of using a beer can shim on a Nitto seatpost makes my skin crawl. I did try sprinking a little dirt on it while I was riding a century a couple of weeks ago and it worked; but it's not the right size!

onespeedbiker

The last frame I bought had the same issue and caused the same ovalization. IOW, it's was most likely the undersize seatpost (27.0) that caused the ovalization! In this case it was so bad I had to de-olvalize the top of the seattube before the larger seatpost would fit. If you do the math it's fairly obvious the smallest measurement of an oval will increase once the oval is made round.

onespeedbiker

Perhaps I am guilty of looking for the answer I already assumed, but yours makes the most sense. As with the old saying (without the moral significance) if the shoe fits wear it! It makes no sense to me to try and make a seatpost size work just because it was the OEM spec. Thanks!

Bill Kapaun

Keep in mind, 0.2MM is only 0.008"

onespeedbiker

Yes, but it is often the difference between slippage and not.

onespeedbiker

Well I resurrected this post first to give kudos to Jeff Willis for how much I considered what he said. Earlier I said that I tried a 27.2 seatpost and it fit. Well, I forgot it was an old Super Record seatpost that needed some resurfacing so the diameter was closer to 27.1. When the 27.2 Nitto seatpost arrived I tried it and indeed it jammed. I took the frame to an LBS I trust to see if it could be reamed out to 27.2. The owner said yes it could be reamed but he would not guarantee it would not compromise the frame. He further said it appears the seatpost has been wobbling, as the first 65mm is about 27.2 but the next 40-50mm narrows (27.mm- 27.1mm) and then farther down it opens up again. As most the experienced posters on the forum suggested, he recommended a beer can shim.

Thinking things over, the only fix I didn't like was the shim; I like elegance and a piece of a beer can is not elegant. So what I did was use a combination of fixes. I first used a brake cylinder hone to clean up and maybe open up the bottle neck a little. I then cut the seatpost down to 200mm and sanded .1mm off the bottom 100mm. A little patience and I had slight step down at the end of the post. Smeared on some grease and the new post fit like a glove; no wobbling and no slipping. There is also nothing to detract from the seat post and there is another 25mm of unsanded post (actually the sanded area doesn't look bad at all) in case it needs to be raised or lowered for a different seat.

BTW I found this describing 853 tubing.https://www.tetcycles.com/Frames/Tubing/tubing.html What I want to know is what the wall thickness numbers mean. I'm guessing it's in millimeters and it's about butted tubing, but the diameter measurements are in inches (I think I read about this mixture of millimeters and inches somewhere but my memory is not what it used to be).

spinbackle

I have a '99 Peloton that I built up from a NOS frameset. I used a new 27.2 Thomson seatpost from the get go and have had zero slippage.

DannoXYZ 

I hate that the U.S. is the last bastion of the old Imperial standards. Heck, even the U.K. is metric nowadays. I have two copies of Solidworks installed, one for SAE measurements and one for metric and I have to convert my drawings between the two depending upon which supplier I'm ordering from...grrr..

Anyway, inch measurements are often used to specify the outer-diameter of the tubing. While mm measurements refer to the wall-thickness of the tubing. In the old days, you had bikes with 1.125" down & seat tubes, 1" top-tube. To compete with aluminium and CF frames, manufacturers have upgraded the sizing to yield lighter and stiffer frames. The numbers you see are typos, they represent the thickness of the tubing at the ends and middle:

0.65/0.4/0.65mm are double-butted tubes that have 0.65mm wall thickness at the ends where they face higher torsional and bending loads and the middle is thinner to save weight without much of a strength/stiffness penalty. The thicker ends are also to deal with the heat of welding/brazing. Similarly...

0.7/0.4/0.7mm is slightly thicker
0.8/0.5mm is thicker still and is typically a single-butted seat-tube. The thicker end is down at the bottom-bracket.
0.9/0.6mm is even thicker and used in larger sized frames.