Seat tube out of spec: customer vs bike designer

[matteof93]

I have just bought a steel frameset to build my first gravel bike. The frame is designed by a small company in the EU and then manufactured in Taiwan.
When it arrived, I noticed that the seatpost could be inserted way too easily, in fact, it slides in without even touching the seat tube.
I measured the seat tube, and I found it to be ovalized: the diameter left to right (drive side to non drive side) is 27.3 mm, the diameter front to rear (front wheel to rear wheel) is 27.5 mm. The frame is advertised as compatible with 27.2 mm...of course it is, but the seat tube should be round and should never exceed +0.1mm with respect to the 27.2 specification.

I contacted the seller, who is also the designer of this frame (I told you it is a small brand). Here are my questions, and his replies.
I think these replies are completely ridiculous, it would have been much more credible to reply something like: "We are perfectly aware of the problem, because that cannot be avoided when producing relatively inexpensive frames in Taiwan. However, in order to account for the problem and maintain the strength and reliability of the frame, we have designed the seat tube to have a wall thickness that is big enough to support the extra load given by the tolerances being not that accurate."

Q: The seat tube of the frame is out of spec. The seat tube diameter is 27.4 mm - 27.5 mm on the Y axis (front wheel to rear wheel direction), ~27.3 mm on the X axis (drive side to non drive side direction).

A: Sorry, but it is normal, all our frames are made it it for several questions:
1) don't damage the seatposts when you insert it on the frame, special the carbon models
2) it is better for reliability if only a small part of the seatpost touches the frame, because then the rest of the seatpost works flexibly and does not regenerate noises when it is dusty, as the clearance is sufficient for the dust not to accumulate.

Q: I have tried 3 different 27.2 mm seatposts (of 3 different brands) in the frame, but they all have significant play in the seat tube, even when fully inserted.
This means that the diameter of the seat tube, across its entire length, is too wide. When the seat clamp is not tightened, the seatpost simply falls into the seat tube until it stops against the upper bottle cage boss. When the seat clamp is tightened to 5 Nm, the only part of the seat tube that is in contact with the seatpost is the area covered by the seat clamp itself.

A: You can apply more torque, like 8Nm or included 10Nm without any problem.

Q: Just below the seat clamp, even when tightened, I can easily slide a 0.1 to 0.2 mm feeler gauge between the seatpost and the seat tube. This will probably lead to the seat post slipping into the seat tube and, in time, it will probably cause the frame to crack just below the seat clamp (because all the stress is concentrated in that point).

A: This point of stress concentration actually works better in flexion than if it is limited by the contact of the seat post with the rest of the tube. The longer the tube length, the better it works in flexion.

What is your take on all this? In my opinion all his replies do not make any sense from a mechanical perspective. He is talking about flexion, but a seatpost should flex exclusively from the seat clamp to the top...and not below the seat clamp. The only frame that is designed to have flex also inside the seat tube is the new Canyon Aeroad, and in that case the seat clamp is moved way lower than normal because the fulcrum of the system must be, indeed, the clamp.
Then he talks about dust inside the seat tube...I mean dust should never enter into the seat tube if the tube is made with the correct tolerances.

[alanyu]

To me, looks like a bullshit designer/company

[matteof93]

To me, looks like a bullshit designer/company

Exactly. At least he agreed on checking the seat tube diameter of a couple of other frames he has in stock...if any difference arises, I hope he will replace my frame.

[TobinHatesYou]

0.1mm is borderline acceptable.
0.2-0.3mm is not.

I’d demand a return and my money back after that conversation.

[Broady]

Just sounds like making excuses for poor tolerance. I'd probably shim it and run it but fully understand if you wouldn't be happy with it.

[matteof93]

0.1mm is borderline acceptable.
0.2-0.3mm is not.

I’d demand a return and my money back after that conversation.

That is what I want to do.

Option 1: he replaces the frame with a new one that is properly made.
Option 2: return and refund.

[matteof93]

Just sounds like making excuses for poor tolerance. I'd probably shim it and run it but fully understand if you wouldn't be happy with it.

The problem is that it is oval...so I cannot shim it easily.

[MrCurrieinahurry]

Id be concerned about the rest of the frame as well.

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[matteof93]

Id be concerned about the rest of the frame as well.

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Good point. If they have that kind of approach...chances are also the press-fit BB and the head tube might have problems.

[MrCurrieinahurry]

Yea i dont mean to put it down anymore but just would defo be delving further into stuff

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[Steve Curtis]

A few years ago, many people had this issue with the London road frames from Planet X.
I suffered with the same problem and they were adamant it was within tolerance.

Even after many hundreds of complaints nothing could be done so most of us chopped up coke bottles or cans to make shims.
Crap, but at least we could ride the things.


Sounds like you need to throw the frame at him.

[matteof93]

A few years ago, many people had this issue with the London road frames from Planet X.
I suffered with the same problem and they were adamant it was within tolerance.

Even after many hundreds of complaints nothing could be done so most of us chopped up coke bottles or cans to make shims.
Crap, but at least we could ride the things.


Sounds like you need to throw the frame at him.

I remember I read about that problem with Planet X...because I also wanted to buy a frame from them since their frames were cheap before Brexit (I live in Italy).
The frame is steel (crmo 4130 double butted), the wall thickness of the seat tube is 1.2 mm...I don't know...maybe given the wall thickness the seat tube is extremely unlikely to crack below the seat clamp.

[ultimobici]

For a frame to have a seat tube so far out of spec is unacceptable. Strip the bike down, box it back up and ship it back for a full refund. While you’re at it, raise a chargeback with your credit card company.

His assertion that it’s normal to allow the post to fit easily is idiotic. Seatposts have gone up in 0.2mm increments for eons for a reason. Shims are always several cms long to allow the post to be supported and the frame protected in the and way as a post.

The idea that you could just whack the torque up to 10nm is equally stupid. Aside from the fact that most clamps are rated to a lower setting, what does he think will happen to a carbon post treated this way.

As Mr Curry says, I’d be worried about the rest of the frame.

Run away, very very quickly.

Finally - name & shame.


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[matteof93]

Ok, so I got an update from the bike brand. They say all their frames are made that way, they have checked a few of them in their warehouse.

Thinking about the problem, it might also imply a safety issue related to the seatpost.
Each seatpost has a minimum insertion length because there is a maximum lever that it can sustain; however, this is evaluated assuming that the seatpost is inserted in a properly made seat tube (meaning, that makes contact with the seatpost along its entire length or at least for a length that is equal to the minimum insertion lenght, such as 80 mm).
In my case, the seat tube makes contact with the seatpost for a length that is equal to the thickness of the seat clamp...something like 10 to 15 mm. I actually think it might be not safe to ride.

[ultimobici]

0.1mm is borderline acceptable.
0.2-0.3mm is not.

I’d demand a return and my money back after that conversation.

That is what I want to do.

Option 1: he replaces the frame with a new one that is properly made.
Option 2: return and refund.

Sounds like you are a little too understanding.

His responses scream incompetence.


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