Sinking Aero Seat Post on TT Bike

The aero seat mast on my Trek Speed Concept gradually sinks during rides. I understand that this is a relatively common problem on TT bikes with aero seat posts. I’ve tried a bunch of things to try to get it to stay up, and it’s better than it was, but it still gradually falls over 2 or 3 rides which changes my position.

I’ve used carbon paste and set the torque with a torque wrench. I’ve also played with shims and tape on the post to try to give it more friction, but nothing seems to hold it in place permanently.

Can anyone recommend some good tips and tricks to help with this problem?

Canyon Aeroad suffers from the same issue, several of my friends suffered from the issue, I got mine and my bike fitter removed carbon paster I had used and user Finish Line Biber Grip, never had the problem, friends have started using the same and their problems have gone away

Not much help … but all I had

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Thanks… I’ve used both Fiber Grip and Park Tool Supergrip. Neither worked on their own.

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What’s the recommended torque setting? I was having issues on the Bianchi so asked my local dealer who ‘off the record’ said they always use 1 Nm of torque more than what it says to use. Certainly sorted mine out and I’m sure Bianchi aren’t the only ones who set these values a bit too conservatively.

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Had the same problem on one of my aeroposts. Tried three different carbon pastes & none of them worked permanently. Was unwilling to violate the manufacturer’s recommended torque spec.

In the end, I pulled the product tag off a Coure Silver Speedsuit & used it as a shim in conjunction with Park Tools carbon paste. Tightened it up to the mid range of the torque spec. It’s held solid and squeak free for a year and a half.

image

It looks better IRL than this photo makes it look but I’d be telling a fib if I said it looks good. Still I don’t think anybody else ever noticed. But it doesn’t slide down three inches in the middle of a ride…in fact it doesn’t slide at all. And it doesn’t sqeak…which was an unexpected benefit.

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silly comment alert

you’re having trouble keeping it up? :slight_smile:

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Too specific. It’s a common problem on every aero post I’ve ever had with an expander inside the frame rather than a clamp :sob:
Here’s what I did with my 3T’s slidey post:

  1. Clean it and the seat tube thoroughly.
  2. Install it with new Muc-Off Carbon Gripper to the manufacturer’s torque
  3. In the trainer, grab the saddle and rock it around
  4. Re-torque it
  5. Repeat steps 3 & 4 until there is no play and the torque settles down (instant click from the wrench)
  6. Do a workout, during this workout stop every 10 minutes to check height and re-torque
  7. For the next week, check the torque and height at the end of every workout.

After a week of workouts very slightly loosening things, I presume that the expander was very slightly moving around, it eventually settled and no longer slips. Let’s see how long my luck holds out. I bet the next pothole or speed bump ruins my streak :laughing:

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Had the same issue on the TT bike I had 10ish years ago.

Doubt I would want to do this anymore, but back then I would scuff the post up a bit with sandpaper to fix this. The scratched up area would provide better grip and stop the slipping. :man_shrugging:

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@Brennus That’s awesome. I’ve done somthing similar using metallic tape (intended for hvac systems). Not sure where I saw that recommendation but someone else told me it worked great for them. It has given the best results so far so I may just add another layer today…

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@rjessop That sounds like a great procedure. I’ve definitely gone over it a few times but not so thoroughly or repetitively. I will definitely play with it some more as you have described. Thanks!

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I haven’t had any problem with the seat post, but I kept getting the slipping problem with the expander cap in the fork steerer, the guy at the bike shop suggested to add some superglue, one drop on “plates” of the expander and just let it set after I retighten everything, works like a charm ever since.

Now I do admit glueing your seat post is a little out there, but perhaps you could use some thing like an “expander” inside the seat post, maybe some polystyrene or the like, just to act as a brace against compaction from the clamp, similar to how the stem and expander work on the front.

Hope it gives you some inspiration.

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@shawrx Well arguably that’s not much different than using a carbon paste that has beads or sand in it (like fiber grip and supergrip). Everything I have ever used one of those pastes on has ended up all scratched up too. It’s painful to see what that stuff does to the bike parts!

@iamkidzor Yeah, I can’t imagine using crazy glue on my post, but your post reminded me that @Jonathan often recommends Rectorseal Pipe sealant to stop threaded parts from creaking and squeaking on mountain bikes so maybe this would be another application for that??

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Heh, my bike did this as well the first ride. My buddy, who’s a mechanic, took it out mid-ride and rubbed some dirt on it. Didn’t slip the rest of the ride. lol. I think I took it out and cleaned it up and used Park carbon paste and it’s been fine since.

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Agreed. Back then I didn’t care about a scuffed up
seatpost. These days I look at my bikes as art and don’t want to jack them up!

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My seatpost was slipping even after trying many of these suggestions, in the end i took it out, masked it up, put 3 heavy coats of paint on the lower section where it clamps, and put some tread grip in between the 2nd last and last coats (basically fine sand for putting on painted stair treads)

Made it a very snug fit that doesnt slip anymore

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@jezza323 That sounds extreme but whatever works! I don’t think I’m quite there yet but I do appreciate the information… Do you remember what kind of paint you used?

just a half empty spray can i had sitting around, nothing special

my frame is a direct from china model, so I wasnt too fussed about it putting some paint on it. Probably wouldnt have done it on a name brand frame unless I was really desperate. It has a terrible clamp mechanism, wedge in the frame type, definitely a bad idea for a seatpost clamp IMO

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Most aero seat posts have crappy wedge clamps just like you describe. At least older ones like mine do. There must be a better way to design these things.

i no rite. My https://masoncycles.cc/shop/categories/bokeh-bikes has a perfectly lovely seatpost with a finish to die for and paste has scoured it :frowning:

My BMC TimeMachine seatpost clamp is a plate behind the post with four 5nm bolts. Never budged a millimetre :smile: There’s always an exception to the slippery aero post rule.

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