jpescatore

Back in December 2019 I bought a Jamis Renegade Escapade to be my gravel/touring bike and what I ride on more relaxed road rides with my wife. Steel frame, carbon fork, crank and seat post, bit 40mm tires. I have about 1500 miles on it, really like the bike.

A few weekends ago, it warmed up into the 50s and was sunny - I decided to take the Jamis out on the C&O Canal Towpath for a 30 mile ride. Very pleasant ride for the first 15 miles out and 10 miles back, but then the seat started to tilt forward. I figured the seat rail bolt had loosened up, just leaned back on it, would look at it when I got back to my car. But then the seat seemed to wobble side to side and I said "Hmmm...," got off to check and saw what preceded this:


That's not good...

The carbon seat post had fractured and I had to do a mix of hike a bike for the very crowded sections of the Towpath near Great Falls and riding standing up holding the seat until I reached my car. Glad I didn't lean back too far/too long - the seat was still on top when I got off, but after just a bit of riding out of the saddle, it completely flopped over.

I had raised the seat recently, so thought maybe I had screwed up with the carbon seat post. I had even used carbon paste to reduce slippage and the urge to over-torque. I checked my torque wrench, I had not over torqued it. The "don't let this line show" line was still in the seat tube, I hadn't raised it too far.

Brought it to the bike shop where I bought it, they were surprised - everyone has heard of this happening, very few people seem to have actually experienced it. There is a lifetime Jamis warranty on the frame but everything else is one year, but Pedal Pushers said they would treat it as a warranty repair, no cost to me - they concurred that I had not over-torqued or over-extended the seatpost. Must have just been a manufacturing defect.

They didn't have the right size carbon seat post, so they put in an alloy one and will call me when Jamis delivers the replacement - with the supply chain delays, that may be a while. But, I think I'm willing to pay the 8oz in extra weight to not have to worry about riding standing up over carbon daggers again...
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chaadster

Yoooooo! That's crazy!

There was a guy over in the Clyde/Athena forum complaining about post slippage with this same frame. The seat collar design seems kinda silly to me, but more importantly and perhaps more relevant, is that he had a lip, or edge, inside the seat tube, so the diameter was not consistent all the way to the top. I don't recall how he fixed it or what became of that-- I'll go check in a sec-- but it makes me wonder if there could be something related to this case, because as you say, it's rare to see something like this. It could be coincidental, but could be not.

EDIT: here's the link to that thread I mentioned: https://www.bikeforums.net/clydesdal...ding-down.html

woodcraft

Yikes!

Any chance that it was damaged by being clamped over-tight in a repair stand?

big john

It looks like the dust/dirt was inside the post, meaning it may have been cracked or compromised for some time. Glad you didn't fall.
btw, it's likely only a 2 ounce difference, depending.

Rage

Dang. That could’ve been real bad.
You’ve got good luck.

jpescatore

chaadster - wish I had seen that post. I had some slippage on that seat post which resulted my chubby thighs (I'm a 225 lb Clydesdale) rubbing on the annoying seat clamp on that carbon seat post. From that post, looks like same seat tube. I raised the tube and used carbon paste and torqued to Jamis spec and it seemed to hold. The seat clamp on the replacement alloy post doesn't stick out as far and seems to have more rounded corners.

The Jamis seat tube clamp uses a two piece arrangement with a very short 5mm bolt on the chain ring side and a collar kind of deal that extends into the clamp on the other side. Doesn't seem very sturdy.

woodcraft - I have a carbon road bike so bought an adapter for my maintenance stand where the bike hangs on a crossbar that is clamped into the stand. Generally just leave it in there for the Jamis, in any case never clamping to the seat post.

chaadster

I can only guess, but I think that the issue, in both cases, could be related to the design of the seatpost clamp (i.e. the clamp on the frame holding the seat post). As was pictured in the other thread, there is an inner diameter change near the top of the clamp, resulting in a sharp-edged lip where the brazed on collar sits proud of the seat tube. That's the bit which the guy in the other thread filed smooth. The issue with that kind of frame construction seems twofold, though, and though the other guy may have removed that edge which I suspect may be a stress riser on the post and part of the reason (if not the cause) for your post's failure, there is still the issue of insufficient clamping area to prevent slippage. Further, even if, as you experienced, the addition of paste helped stop the slippage, there is still that tiny inner diameter difference where the clamping force is not distributed evenly across the length of the post, which may be causing delamination of the carbon fibers.

The construction quality of the stock carbon fiber seatpost could be a factor here, too. If the material has voids, uneven clamping force could interact with those voids to cause delamination. As someone else mentioned, it could be the posts were not round, or perhaps the walls were not uniform thickness. I dunno. If you aren't aware of Raoul Leuscher's YouTube channel, Leuscher Technik, you may find his diagnostic assessment and explanation of carbon fiber construction interesting. I don't know that he's done a vid specifically addressing CF seat posts, but the following vid on steerer tube clamps may help understand some of the dynamics going on at the seatpost clamp:


I'd really advise getting Jamis involved on this, and push them to explain away how the seat clamp design elements-- inconsistent inner diameter, the lip edge-- don't negatively impact the holding security or durability of the carbon fiber post they fitted. Who knows, but they may be willing to replace or defray the costs of replacing the post with a metal unit, or maybe even the whole frame if they recognize it's a design or manufacturing defect at issue. Personally I'd be wary about simply replacing the post with a new one of same, just because I'm concerned that seat clamp design is not good for carbon fiber posts, and really just not good at all. I mean, having the clamp bolt above the clamping zone does not seem the most mechanically efficient location.

jpescatore

I filled out a contact form to Jamis on their web site, telling them of my experience and giving them links to both threads - will post any reply I get.

woodcraft

I was thinking not so much of you, as of a musclebound shop employee.

jpescatore

I received a rapid, but pretty generic response from Jamis:

Replied that I'd like to hear if they have seen other slipping/fracturing of this seat post, any redesign or will the replacement be the same, and if any upgrades to the seat tube clamp approach.

jpescatore

A bit more detailed response from Jamis:

So, either just manufacturing defect or when the bike was put together, it was over-torqued and the seat post was damaged.

The seat clamp issue is just a bad choice of seat/seat post combination - for many riders the seat position (in my case 3/8 in back from "neutral") causes the square edges of the seat clamp to be outside the "shadow" of the seat. Longer legged cyclists probably would never hit the problem.

popeye

According to my bro in law you were fortunate you did not have to ride home 10 mi standing like he did holding the saddle.

jpescatore

Yeah, the cycling gods were smiling - could have been 15 miles worst case!

Actually, if I was a bit smarter, I would have made it back. When I first felt it, I thought the seat rail clamp as slipping, causing my weight to slip forward. So, I moved back and overweighted the back of the seat, thinking I'd wait til I got back to look at the rail clamp. If I had gotten off and checked, I would have avoided making it worse and probably could have made it back sitting gingerly...

Was your brother in law riding a Jamis with a carbon seat post?