any advice on a 28.0 seatpost?

[cash05458]

Hey, just started building a C50 and wanted to use my 27.2 thomson post. Of course, the c50 takes a 28.0...bought a use shim that is supposed to be a 28.0 shim but when that is inserted in frame it overlaps on the edges and at that point, you can't then get the 27.2 post in...wondering if they sent me the wrong shim or maybe I am missing something? Any advice? anything else I might try if the shim won't work? tricks? I would really like to stay away from having to buy a 28.0 post btw...thanks!

[DfCas]

Buy any shim that takes up 0.8 mm. A 25>25.8 or a 25.4 > 26.2. I have an older carbon frame that takes a 28 and I use a 27.2 in it with a shim.

[charliedid]

Buy a proper seatpost is my suggestion.

[Black Dog]

Thomson posts are very close to 27.2 and as such have very little wiggle room. Try another 27.2 to see if it is the post or the shim that is causing the right fit. If you have vernier calapers you can take a quick measurement of each and find out also.

[Peter P.]

I'm with Black Dog; measure the I.D. of the seat tube to see if it's really 28.0mm. Is that really what Colnago specs?

If the numbers are good, then you should contact a Colnago dealer and get the correct shim.

As far as I can tell, neither Cane Creek (https://www.canecreek.com/product/seatpost-parts-accessories/) nor Problem Solvers (https://problemsolversbike.com/products/cockpit/seatpost_shims) offer a shim to solve your problem, so if a shim exists it must be proprietary to Colnago.

There is a 28.0mm Colnago seatpost for sale on eBay (https://www.ebay.com/itm/NOS-VINTAGE-COLNAGO-CARBON-SEAT-POST-28-00mm-x-315-mm-218-grams-C40-C50/352563623072?hash=item52166df4a0:g:weoAAOSwQDdbnlC O) for the low, low price of $190!

[Kirk007]

If you change your mind about buying I have a like new WR Composition that I bought for the brief time I had a C50.


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[cash05458]

Well, measured...frame is def. a 28.0...and I have a cracked 28.0 carbon post here...unusable of course...but that fits perfectly...the thomsom measures 27.2...so it's a shim problem...

[cash05458]

Peter...yeah, I saw that on ebay...def. not the direction I wanted to go in...there is another one on there for 199 plus 18 postage...:cool: But will talk to Kirk and see what's out here as well...might as well do it right.

[Joxster]

Been down the road of using shims, just buy a 28.0 seatpost and be done with it. The number of rides I've been on and had slipage because of the shim, and the rides where I've thought theres been slipage................. It's a pain in the thighs

[oldpotatoe]

Well, measured...frame is def. a 28.0...and I have a cracked 28.0 carbon post here...unusable of course...but that fits perfectly...the thomsom measures 27.2...so it's a shim problem...

Get one of these..USE, sold/used many..Great product.

https://ultimateuse.com/spares-and-accessories/seatpost-shims/272mm-id-shims

[Peter P.]

Been down the road of using shims, just buy a 28.0 seatpost and be done with it. The number of rides I've been on and had slipage because of the shim, and the rides where I've thought theres been slipage................. It's a pain in the thighs

I don't know the exact circumstances under which you experienced slipping with a shim, but I have a Cane Creek shim for my Soulcraft (the frame is designed for a 30.0mm post, but Sean supplies the shim for 27.2 usage) and have no problems. And I'll admit I wasn't personally thrilled to use a shim when I ordered the frame, fearing slippage. My lack of problems could be because Sean is a meticulous machinist and it is a custom frame.

[jamesau]

I have a C50 and use a USE thermoplastic shim with 27.2 Reynolds carbon post. It all installs intuitively and has never slipped under my 190ish pound self.

[El Chaba]

The *RIGHT* way to do it is with a 28.0 post...and they are still available new from WR Compositi. Having said that, a really nicely made shim might actually be better at spreading the clamp load over a carbon post if oriented correctly...

[oldpotatoe]

The *RIGHT* way to do it is with a 28.0 post...and they are still available new from WR Compositi. Having said that, a really nicely made shim might actually be better at spreading the clamp load over a carbon post if oriented correctly...

IMHO, ANY carbon post that is secured by a seatpost CLAMP..turn it around 180 degrees to try to ensure the 'hole' is as round as possible when tightening or use a Campagnolo seatpost clamp. Seen more than a few carbon posts cracked by the clamp.

[ultraman6970]

I dont know if anybody mention this... the seat tube in those c50s is not always 28 :D Great for colnago tho, he made sure the darn seat tube wont slip down.

Even with 28mm colnago seatpost you can have a really hard time to put those things in to the point that some sanding needs to be done in the seatpost, just scuff the clear coat off.

I have one of those USE shims and are the right thickness and well measured all over, wonder if you got the right thickness but the wrong diameters, like for a 31.2 (or whatever) and thats the reason is overlapping? IME the USE shim should not overlap because are a good product.

What the op can do is just a pair of scissors and cut a few mm left and and right of the shim? suggesting scissors because the shim is like paper. OP definitely you have to measure the thickness of that shim 1st ok?

[weisan]

he's good.

https://forums.thepaceline.net/showthread.php?t=232991

[cash05458]

well, silly me...so altho I had ordered a 28.0 shim...just checked the box I had tossed into the trash it came in and see they sent me a 30.0 shim instead...so that would explain all the confusion...went ahead and ordered another at 28.0...thanks guys!

[DfCas]

At one time Kalloy made a cheap 28.0 post and I have at least 1 in the parts box. Don't know if it is still available but may be worth investigating to have a backup post on hand.

I use an USE shim and a 27.2. Never a slip.

[ultraman6970]

THe 28 use shims are hard to come by lately, like if use stopped making them.

[DfCas]

I used a 25>25.8 shim. Worked fine.

[jemoryl]

For awhile I rode a bike, a steel Basso Viper, that required a 30.0mm post with one that had a 29.4mm diameter plus a sheet of brass sheet metal of the correct thickness. I simply calculated the needed thickness and found a variety of thin brass sheets in a hobby store. Worked fine for several years until I came upon a 30.0mm Thomson.