neo_malarkeyist

Recently got my hands on one of the rather elusive and mysterious (according to this forum at least) Raleigh sp-1000s from the early 90's. Love the thing already—it's mint condition, rides like a dream, and was an absolute steal at $150. I'll post some pics if people want to check it out. It's been fun reading the past threads about them.
Slowly working my way through some part switches and dialing it in. The original seat post is just a tad shorter than I'd like it to be. The seat post diameter is 26.6mm, and after not finding many appealing long 26.6 posts online I opted for an Aliexpress carbon post in 25.4mm and figured I could just shim it up. Curious if anyone else has used shims with carbon seat posts—I've seen a lot of threads about shimming in carbon frames, but not the other way around. Wondering if there will be issues with slippage or anything?
I figure it's safe as long as it's not over-torqued and fits well. Anyone have experience with this? If not I'll report back after I get the shim. If it's a bust, the carbon post was only $20 (gotta love straight from china).

cxwrench

No way in hell I'd trust my well-being to an Aliexpress carbon post. That said if you had a good quality post I would be fine with shimming it.

Polaris OBark

I accidently bought the wrong diameter Salsa carbon seat post, so I ordered a shim. But Salsa it turns out actually warns not to do shim a carbon seat post.

Ever.

There are two concerns. The first is that pinching at the slot will damage the post, and second is the concern that effectively you will be using minimal (say 100 mm max) indirect contact with the seat tube on the frame, which can put undue stress on a small section of the post.

If this is a problem for a Salsa post, presumably a "good-quality" post, it is going to be much more of one for a cheap unbranded one where liability is evaded.

The main problem is that a fractured $20 cheapo carbon seatpost could do far more than $20 worth of damage to the hapless rider.

masi61

I have a Ritchey Superlogic 350mm 27.2 post that is shimmed in a 30.0 seat tube on my titanium “Veritas” bike. I tried 2 different aluminum ones and they both creaked. I then happened upon the “U.S.E.” Delrin (nylon) shim and was finally able to get a snug fit that does not make me want to over tighten my seat binder bolt to remain creak free. The U.S.E. ones if you can find that brand (the company is English) are a little longer than the inexpensive Chinese ones.

FBinNY 

There's nothing inherently wrong with using a well made shim. It should be about 2.5" or longer (2x diameter +).

To ensure against stresses from ovalizing, Grease the outside of the shim (between shim and frame) well, and orient the shim's slot away from the frame"s. Also, assemble the post into the shim dry to lower the camping force needed to prevent slippage.

If I had my choice, I'd use an anodized shim to prevent/reduce corrosion, but it seems that everyone isn't doing so, and I haven't heard of any issues.

neo_malarkeyist

I've heard surprisingly good things about Aliexpress carbon products. I have a few buddies that have been running all their carbon bars, seat posts, and saddles from Aliexpress without issues for quite a while. Guess they're made in the same factories as a lot of the major brands, just no labels. I just got the post and it looks as legit as any name brand post I've seen. We'll see how it does though!

veganbikes

That is a guess. It generally not correct there is no third shift or magical backdoor producing the same parts and scooping some extras for private sale. You do you but carbon is a more specialized material and I would want it from a trusted source either here or overseas.

Also if I am buying from Alibaba and his 40 thieves why not just get one of them to build you a post in the correct size. It is dumb to want to shim a cheap-o post from an unknown source when there is probably one either already in the correct size or could be made by one of these brands. Me personally would rather just get a good reliable post from Thomson or get a titanium post from say TiCycles (Dave is awesome) and not worry about carbon.

easyupbug 

This is difficult as they do exist. Having done industrial vendor evaluations in the PRC in the early 2000s I saw production lines of identical parts final stage packaging/palleting with Chinese manufacturers labeling with the next pallet of identical parts down the assembly line all clearly packaged as Crane valves of Ipswitch, United Kingdom. That said the Chinese are incredible at low quality excellent appearing products, the Silk Street Market in Beijing is known World wide for selling fake name brand items and gets over 10,000 visitors/buyers a day.

squirtdad

I think the keypoint is that the quality is hit or miss, the products may be great or the may not be, there is no way of knowing, but a seatpost failure would be painful I personally stick with aluminum and would never consider a non verifiable source for one

counterfeit is real, and in some case hard to detect, like counterfeiters making frames that weigh the same as the real thing https://www.velonews.com/not-all-fra...terfeit-bikes/

icemilkcoffee 

There are tons of 26.6mm seatposts on Ebay. How long a length do you need?

As to carbon 25.4mm seatpost with shim- I did the same thing with my Centurion Ironman and had lots of issues with the seatpost slipping. I don't know if it's the small diameter seatpost, or the aluminum shim, but it just did not like to stay put. I switched back to an aluminum seatpost with no shims and it had zero problem with slipping.

Atlas Shrugged

The OP was looking for an economical solution and now we are recommending a custom titanium post? Other than bicycle forks I can’t think of more silly use for titanium than a seatpost. There are literally millions of carbon seatposts in use and nobody is worrying.

veganbikes

I actually recommended a Thomson post but I recommend Dave at TiCycles because he makes relatively cheap stuff in the US in whatever size they might need since the likely want for carbon is either weight or some sort of comfort.

easyupbug 

Is carbon post considered more comfortable? I am sensitive to carbon being better in handle bars as I have arthritis in my hands and wrists but developing in my back so seat posts are of interest. I enjoy a trike for bad arthritis days but would like to keep it to a minimum.

FBinNY 

A few things to consider.

1 - while there are some inherent differences between the various materials used in bike making there are greater differences resulting from how those materials are used. So it's possible that a carbon seatpost might give you similar benefits as your carbon handlebars it's equally possible that it won't.

2- a major difference between handlebars and seat posts is the unsupported length. A seatpost is a relatively stout component compared to the bars and that's such we'll never give you that kind of flex.

3- also consider the inertial mass. Unless you're riding with elbows locked the inertial mass of your hands and lower arms is tiny compared to the inertial mass of your torso when the saddle has to lift it.

If you're concerned about your back either learn to ride lighter by anticipating shocks and lifting yourself out of the saddle a bit or consider a suspension seatpost.

I'm not trying to talk you out of trying a carbon post just trying to help keep your expectations reasonable.

easyupbug 

FBinNY, you sir have nailed it. I will look into my carbon posts more carefully (I have too many bikes) as I for the reasons you espoused have found carbon bars helpful as I strive to remain up right cycling. Being a mechanical engineer by training and vocation coaching is helpful in my understanding of my growing frailties. You are correct as to bumps, I am always up on the pedals. Osteo arthritis has brought a new level to the earlier rheumatoid arthritis.

icemilkcoffee 

That carbon fiber seatposts dampen vibrations is not a myth. It's been tested and it's a very significant effect. The longer the seatpost showing, the more significant it is. Likewise with setback- more setback=more shock absorption.