Madone SLR - Slipping Seatpost
 

This happened to me on a ride yesterday! I have a 2019 Madone SLR and noticed creaking from the saddle/seatpost area while in the saddle. The noise would go away every time I would get out of the saddle. I took it to my dealer and he showed me how loose the seatpost was. I'm not sure about this, but a few days before I adjusted my Iso speed to make the bike stiffer. Maybe that could have had an affect on the seatpost too as the L shape iso speed is connected to the seatpost. Good to know I'm not the only one.

If it is torqued to spec, should not be slipping. This is very strange. Especially if using carbon fiber grip paste.

I would contact Trek and ask for a fix or my money back. Those are expensive bikes.

I had the same problem with my Domane. Dealer gave me a torque wrench for the seat with advice never to use anything else. The wrench is rated at 5 nm; the seatpost seat clamp spec is 6-9nm. I tightened my seatpost up to 7 nm and no more slippage.

This isn't a problem limited to Trek. It seems that all the bike companies who have gone to the "hidden" / integrated seatpost clamps are having the same issue. My first 2019 BMC SLR01 had the same problem -- curable only for brief periods of time -- until BMC eventually replaced the frameset. The replacement frameset hasn't had the same problem, but the post height is clearly marked and I check the torque at least once per month. (It's on my calendar.) The benefits of these clamps are purely aesthetic -- there's no meaningful aero benefit because of the location of the seatpost clamp. Sometimes, the manufacturers "innovate" purely to please the marketing department. And the buyers pay the price. Very frustrating.

"This isn't a problem limited to Trek. It seems that all the bike companies who have gone to the "hidden" / integrated seatpost clamps are having the same issue."

This is an age old problem with hidden post binders, wedges, etc. They have always done this as everything is conspiring against the "clamp" system. Gravity, weight, movement, etc. all want to drive the post down into the frame. If I recall correctly Profile had the Fly bike with a hidden binder and it did this. There have been steel and aluminum frames with wedges and hidden binders that did this. Nothing new in cycling, is there?

Took my Madone SLR out for its first proper long ride (60m) today. Exact same problem. It had dropped by 3-4cm by 15 miles in. The Trek assembly manual doesn't seem to have the recommended torque for these bolts, but I was doing it by hand anyway. After the problem showing up more than once, I tried to give it a little extra torque the third time (there's grip paste in there from the LBS) and I did each bolt at least twice - it seemed to hold for the rest of the ride. Not a huge body of evidence but I'm hoping that's done the trick.

Update: 5 Weeks & 1600 km On
 

No slippage since I cleaned and re-installed the seatpost. Reiterating that I torqued the lower bolt first then the top bolt using the 5.2 Nm torque key that came with the bike.

Thanks, interesting.

Checked mine with a torque wrench last night and it was >8Nm. I didn’t want to push the wrench any higher. If it slips now I’ll get the shop to sort it rather than risk over-stressing it.

There's always the pro solution seen at Paris-Roubaix, aka the taped up hose-clamp

https://cimg9.ibsrv.net/gimg/bikefor...d8b1e60f81.jpg

https://cimg5.ibsrv.net/gimg/bikefor...1d52b838ad.jpg
https://cimg0.ibsrv.net/gimg/bikefor...c7d1f81144.jpg
My seatpost keeps getting loose by rocking back and forth. The plastic cover hides two bolts that tighten the L Shaped ISO Speed and seatpost. I have to tighten it every few rides.The rail on the back is for adjusting saddle height. Efeeing pain in the ass!

I had cleaned my seatpost wedge etc as @Cyclefiend suggested but I still lost 1cm in 30km. So I took it back again.

I think mine has been dropping (only had it 2 weeks) when the isospeed has moved a lot, it does seem to be the back/forth movement that prompts it to slip but that coincides with hitting vertical drops in the road so it's hard to be sure.

I don't think anything holding the seatpost is under that plastic cover in your first photo. I don't think there's any reason to go inside there unless you're replacing the isospeed mechanism.

The only thing holding the seatpost up is the friction between the wedge at the front of the post and the inside front of the tube, and the two edges at the back of the post against the inside of the back of the tube. And that is done by tightening the two 5mm hex bolts (ideally using a long torque wrench attachment) in the slot at the back of the post which your second yellow arrow points at.

BUT that pressure/friction maxes out once those bolts are in as far as they can go. You can put as much torque on that as you like (don't try) and it won't push the wedge any further forward because they physically run out of thread. The ends of the bolts just go into two threadless hollows on the back of the wedge to force it forwards.

Apparently Trek told my retailer to cut off two washers from those bolts which then allows them to push the wedge a little further (using the recommended 7Nm). This is obviously a slightly insane engineer's response to a design or manufacturing tolerance failure but they've done it anyway.

I'm going to test it today. (edit: I am reviewing this plan in light of the massive hail storm that just began)

... As an aside, I've spoken in person to 3 Madone 2019 owners - of a 6 disc, 7 disc, and 8. None of them have had this problem and two of them are heavier than me.

Very good post. I've got a SLR disc (just built up from the frame) so have been following this. Mine slipped after my first ride, but after putting friction paste all has been good. I was going to ask about weight, but you covered that in your post.

Maybe this isn't relevant but thought I'd throw it out there. Have you compared saddle position to those of the other 3 owners you spoke of. Meaning the forward/back position relative to the post. I'd imagine that could change the amount of pressure at the contact point of frame/seatpost.

Thanks. :)

I haven't, I did wonder about that - mine was approx 8cm offset* from the nose of the saddle to the crank vertical, but I've changed saddle to my trusty Selle Italia C2 so it's probably slightly different now. I've just emailed the other owners to check...

* I've got the normal seatpost, I think there are options on a custom Madone to have one that curves further back?

Not sure about the curving back bit, but I know there's options for height of the seatpost.

Well the surgery seems like it might have worked. Did the exact same 32km route that lost me 1cm the other night and it seems fine. Felt more solid too. Fingers crossed!

Trek slipping seat post
 

Just purchased Trek madone and guess what - seatpost slipped on first ride. Back to retailer who also informed by trek to cut the washers from the bolts. I pick it up tomorrow. Give me good news - you’ve had no problems since ???

Good news indeed. Did a 50 miler Sunday and no problems. Measured my crank-saddle afterwards and still the right distance. Reasonably bumpy roads at times too. Seems solid. Make sure they don’t over-tighten it though ;) I’m sure they know what they’re doing.

No problems since & I've probably got something like 2k miles on it. Hit some rough bumps and potholes during one event & no movement.