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Seatpost - Seat Tube Clearance - How much is too much?

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Seatpost - Seat Tube Clearance - How much is too much?

Old 11-18-22, 03:33 PM
  #26  
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Originally Posted by FBinNY View Post
For example, the OP might send the builder a link to this thread. In doing so, he can state that he's kept the maker's out of it out of respect, but will post the outcome once there's closure.
That might have some value...Builder can see how others perceive the situation. But I suspect he/she is more likely to think, "Shoot, I build frames for a living -- I know more than a bunch of keyboard jockeys."
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Old 11-18-22, 03:43 PM
  #27  
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Originally Posted by Koyote View Post
That might have some value...Builder can see how others perceive the situation. But I suspect he/she is more likely to think, "Shoot, I build frames for a living -- I know more than a bunch of keyboard jockeys."
There's always that. However, read Admiral Hopper's quote below.

Nobody's opinion counts nearly as much as the actual measurements and specs.

The OP needs to convince the builder to consider whether he can defend his claim that the frame is within spec.

Last edited by FBinNY; 11-18-22 at 08:20 PM.
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Old 11-18-22, 06:12 PM
  #28  
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Originally Posted by Steve_sr View Post
The Thomson post shown in the photo is 1.245" (31.62mm) The frame measures 1.265" (32.13mm). The seat tube is clearly over by .020" (0.5mm)




The post should fit without an insert. The insert is built into the frame.




This is supposed to be for a standard size 31.6mm seatpost. Is there a standard 31.8mm seatpost? Another thought... Is there a standard 31.8mm reamer? Could the wrong reamer have been used?
Guess what? the SEAT POST IS THE PROBLEM. Buy a Correct 31.8mm Post and sell that overpriced Thomson oddball as scrap. Thomson is Known for UNDERSIZED posts.... I've ran into this issue before.. they are MARKED at the correct size but are NOT the size it's marked as.
check it out....
https://bike.bikegremlin.com/3114/se...zes-standards/

tip: several Trek bikes use 31.6mm seatposts... market your ill-fitting Thomson as a Trek part.

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Old 11-18-22, 06:54 PM
  #29  
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Originally Posted by maddog34 View Post
Guess what? the SEAT POST IS THE PROBLEM. Buy a Correct 31.8mm Post.....
2 points to consider.

1 (assuming that the OP measured accurately) a 31.8mm post won't help, it'll only be less wrong, which isn't the same as right.

The standard for seat tube bore is 0.05mm (max) over the nominal. So the OP would need a 32.1mm post.

2- the CORRECT size is what the maker specifies. A substitute may be work if the maker doesn't met his own specs. That would solve the problem, but wouldn't be correct, nor make the frame right.
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Old 11-18-22, 07:06 PM
  #30  
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Originally Posted by FBinNY View Post
2 points to consider.

1 (assuming that the OP measured accurately) a 31.8mm post won't help, it'll only be less wrong, which isn't the same as right.

The standard for seat tube bore is 0.05mm (max) over the nominal. So the OP would need a 32.1mm post.

2- the CORRECT size is what the maker specifies. A substitute may be work if the maker doesn't met his own specs. That would solve the problem, but wouldn't be correct, nor make the frame right.
Two points to consider:
1- the largest seat post sold is 34.9mm.. the SECOND largest size sold is... 31.8mm

2- .05mm is... .002"...or one average human hair, roughly. most machined metal parts use +/-.002" as a mfg. Tolerance.. seat posts tend to run up to -.020" out of standard.

...

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Old 11-18-22, 07:51 PM
  #31  
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Originally Posted by maddog34 View Post
Two points to consider:
1- the largest seat post sold is 34.9mm.. the SECOND largest size sold is... 31.8mm

2- .05mm is... .002"...or one average human hair, roughly. most machined metal parts use +/-.002" as a mfg. Tolerance.. seat posts tend to run up to -.020" out of standard.

...
I don't know your experience in things like this, so I'll just state some of mine.

I ran a manufacturing business and many in the bikw industry are still using tools they bought from me almost 50 years ago. So, I know about manufacturing to tolerance.

Specific to this application, reamers can consistently produce round holes to tolerances nearer to 0.0002" (yes, a fraction of the thickness of hair) than to 0.002" so reaming a seat tube to the specs I referenced is very easy.

BTW - before retiring I sold various cutting tools to builders and shops, including BB taps, various mills and faces and SEAT TUBE REAMERS. I'd have been very upset to hear that one of my clients couldn't hold tolerance.

Last edited by FBinNY; 11-20-22 at 10:05 PM.
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Old 11-18-22, 07:59 PM
  #32  
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Old 11-18-22, 08:03 PM
  #33  
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Originally Posted by FBinNY View Post
The OP should hold off satisfying people's curiosity, and preserves tactical options.
We are not quite there yet...

The bike was ordered as a custom less wheels. The bike was supposed to have been assembled with surrogate wheels, checked out, and then shipped. Apparently that didn't happen. I was planning on doing some minor assembly as I eventually would need to do maintenance on it. Today I went to put the RD on only to find that the chain had been cut too short. It also, mysteriously, came with an "upgrade" bottom bracket. I assumed that this was just what they could get during the pandemic. Guess what? The too short chain matches the bottom bracket. It looks like these parts had been taken off another build and the chain was never checked. So now I have to get a new chain to go with the new seatpost clamp... The saga continues...
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Old 11-18-22, 08:18 PM
  #34  
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Originally Posted by Steve_sr View Post
We are not quite there yet........

Guess what? The too short chain matches the bottom bracket. ..
Curious, what do you mean "the chain matches the BB"?
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Old 11-18-22, 08:22 PM
  #35  
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Originally Posted by FBinNY View Post
Curious, what do you mean "the chain matches the BB"?
THis was supposed to be a Shimano 2X GRX build but showed up with a Dura-ace BB and chain.
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Old 11-18-22, 08:32 PM
  #36  
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Originally Posted by Steve_sr View Post
THis was supposed to be a Shimano 2X GRX build but showed up with a Dura-ace BB and chain.
I see, but that has nothing to do with length, which is a function of chainstay length and sprocket sizes.

Anyway, other than inconvenience, this is strictly a minor side issue.

In any case, you need to get the maker to resolve the issue and correct any material issues. In the event he remains adamant, I have a suggestion. There are a number of builders and knowledgeable proshops in Colorado, (and/or) near you. See if the maker is willing to appoint a mutually agreeable referee to determine if the bike is to spec, with the understanding that the maker will correct it if necessary. Also, the referee's fee would be agreed to in advance and paid by the loser.
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Old 11-18-22, 11:05 PM
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Originally Posted by Steve_sr View Post
The specs on my frame drawing say 31.6mm. I don't think that there is a standard 31.8 seat post. I think a lot of folks get confused as 31.8mm is standard clamp size for handlebars.
No, there's no confusion between seat post and handlebar clamp size here.

Seat posts are still being made in the 31.8mm size. Here's an example by Kalloy.

So yes: 31.8mm is an uncommon but "standard" (or if you prefer, "still in production and available for purchase") seatpost size.
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Old 11-19-22, 11:35 AM
  #38  
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Originally Posted by FBinNY View Post
it'll only be less wrong, which isn't the same as right.
Not speaking to the case at hand, but when "less wrong" comes within tolerance, it IS "right".
The builder should make this right being it's a new frame. That being said, if one runs across this on a used bike, a 31.8 (which used to be a common size before aero became a thing) a post that size, and a more appropriate clamp will solve the issue.
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Old 11-19-22, 05:21 PM
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From looking at the photo it's hard to see if the actual frame keyhole is too far compressed. It may be just the clamp is an ill fit to the outer seat tube dia. You may just need a different/better clamp.
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Old 11-19-22, 07:44 PM
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Originally Posted by Crankycrank View Post
From looking at the photo it's hard to see if the actual frame keyhole is too far compressed. It may be just the clamp is an ill fit to the outer seat tube dia. You may just need a different/better clamp.
Here is a better photo with the clamp tightened to 5nm. Without the clamp the sides of the slot are parallel:


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Old 11-19-22, 07:45 PM
  #41  
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Originally Posted by wheelreason View Post
Not speaking to the case at hand, but when "less wrong" comes within tolerance, it IS "right".
The builder should make this right being it's a new frame. That being said, if one runs across this on a used bike, a 31.8 (which used to be a common size before aero became a thing) a post that size, and a more appropriate clamp will solve the issue.
Other than semantics, specs (including tolerance) determine a binary right and wrong. A part is either within spec or it isn't.

My statement characterizing the 31.8mm post as "less wrong" was because 31.8 is still too small for a seattube bore of over 32mm. It's an important distinction because seatpost fit isn't simply a technicality. Those who've marred brand new posts might curse makers who seem to hate seatposts, but shouldn't. A post has to fit with no wiggle room because it's only constrained at the clamp, and free to rock within the tube under load. That can cause creaking when hill climbing.

Moreover on frames of this design, with the seat tube extended above the top tube, seat post fit is even more critical. The extended frame tube isn't strong enough to function on it's own and relies on the post to contribute support, and carry loads down below the top tube joint. The loose fit will allow the post to rock, denying the critical support called for, and eventually cause tube failure. (eventually can be a long time, or not and a quick search will find many examples of this kind of frame failure)

So, while using a less wrong post might be an acceptable option for salvaging a junkyard find, it's not appropriate here. The ONLY remedy is to rework the frame so it will properly fit the spec'd 31.6 post. Fortunately it's only a matter of replacing the aluminum liner.

As it stands now the OP is now in a situation analogous to going to a celebrity chef's restaurant, and getting served reheated leftovers.

FWIW- all my posts here are based on the OP's measurements, however the photo of the clamp seems to support them as accurate.
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Old 11-19-22, 08:38 PM
  #42  
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Originally Posted by Steve_sr View Post
Here is a better photo with the clamp tightened to 5nm. Without the clamp the sides of the slot are parallel:


Looking at and extending the sides of the slot, I estimate that the tube is nearly closed on itself at the top.

This wouldn't pass muster on $100 dollar department store bike.

BTW - if this bike is ever taken out in weather the loose post and rear facing slot would pretty much guaranty water in the BB.

Last edited by FBinNY; 11-19-22 at 09:17 PM.
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Old 11-20-22, 01:50 PM
  #43  
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Originally Posted by Steve_sr View Post
Here is a better photo with the clamp tightened to 5nm. Without the clamp the sides of the slot are parallel:


Yeesh. The seat post on my late 1990s old straight-gauge 4130 road bike fits much better than that. And it's a mass produced, TIG-welded frame that was probably no better than upper-entry-level or lower-midrange for a road bike of its day.

I'd expect way better than that on a custom Ti frame. It also makes me wonder what else might have been done improperly.
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Old 11-20-22, 02:11 PM
  #44  
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Originally Posted by Steve_sr View Post
Here is a better photo with the clamp tightened to 5nm. Without the clamp the sides of the slot are parallel:


Wow.
If it were me, I'd be livid.
There is simply no excuse.

I'd be inclined to ask for my money back & I'd be happy to pay shipping & restocking fee just so I could bad-mouth this shoddy builder freely.
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Old 11-20-22, 07:46 PM
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Well, there was/is/maybe a local Ti frame builder that I only found out about after I ordered this bike. He shut down during Covid because he couldn't get the components to finish a bike. I looked last night and his website is still up and running so he may be back in business. I'll reach out to him to see if he can replace the insert and what it might cost.

In the meantime if anyone can show instances of frame failure on a TI frame caused by this defect. I would be interested. My Google search didn't turn up much. However, I did find one place that apparently fixes TI frames - https://www.ticycles.com/repair
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Old 11-20-22, 08:19 PM
  #46  
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If only the clamp's ID were the issue one could shim just that and the clamp wouldn't be on the edge of closing up. However I agree with Francis in that the slot also looks to be closing up.

If a 31.8 post did fit and reduce/solve the clamp's closing up I would suggest living with that. But I don't remember the OP even trying this cheap fix. Seems that there could be more at stake in his eyes than a well riding bike.

There are reasons why a reamer cuts off size. Piece holding, cutting edge sharpness, lube among the biggies. I suspect the builder used a straight flute reamer, given the "The reamer apparently can't ream through a discontinuity (cut) in the sleeve" comment. If the reamer is an adjustable one chips stuck in the reamer blades' slots, or poorly seated blades, can also affect the cut diameter. A spiral reamer would reduce both concerns by a lot...

I do like the suggestion to have a third party expert get involved. But having been on all three sides of this possibility over the years I wouldn't hold my breath on the frame's builder accepting this assessment/arbitration. In the end the leverage a customer has, besides the bank/credit card claim possibility, is that of poor notoriety. I hope the builder cares about his reputation and steps up to work out a solution before that "nuclear option" is taken. Andy
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Old 11-20-22, 08:56 PM
  #47  
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Seat post fit and sizing is a repeating topic here. A few years ago i, actually, measured some "27'2"mm posts I have and posted their measurements. here's the link to that thread Another delay seat post size - Bike Forums . My measurements are in post 8. Andy
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Old 11-20-22, 10:01 PM
  #48  
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Originally Posted by Andrew R Stewart View Post
.....

If a 31.8 post did fit and reduce/solve the clamp's closing up I would suggest living with that. But I don't remember the OP even trying this cheap fix. .....

There are reasons why a reamer cuts off size. .....
2 points, we're not talking about a cosmetic issue, nor about a reconditioned used bike. It's s a pricy new bike, so I don't see any reason the OP should accept anything less than 100% right. The seller MUST make it right, so the focus should be about making that happen.

As for reamers cutting off size, consider that reamers as a class are intended for close tolerance precision work. As I posted earlier, holding tolerances of 0.0002" (0.0005mm) is par, so there's no excuse for this kind of sloppiness.

FWIW I suspect that Andy is thinking about the kind of adjustable reamer many shop use. However, a true 31.65mm reamer made for this kind of work costs about $100 and will cut hundreds of frames on size between grinds.

At some point the OP will have to explain to the builder that right now he's only asking that it be corrected, however if it becomes a legal issue he'll be seeking a full refund.
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Old 11-21-22, 02:16 AM
  #49  
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Originally Posted by Andrew R Stewart View Post
Seat post fit and sizing is a repeating topic here. A few years ago i, actually, measured some "27'2"mm posts I have and posted their measurements. here's the link to that thread Another delay seat post size - Bike Forums . My measurements are in post 8. Andy
Measured a couple I have laying about just now:

Thomson Masterpiece 31.60
Thomson Elite 31.57
C-Record 26.76
C-Record 27.15
Croce d'Aune 27.20
DA 7200AX 24.98
Record Dart 27.16
Time Spirit 27.21
Chorus ss 27.14
Record Ti 27.11
Record Carbon 31.54
Nuovo Record 27.16

Thomson Masterpiece and Croce d'Aune are dead on, Time with the only oversized one, and the Record titanium propping up the rear.

I may have too much stuff for my own good
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Old 11-21-22, 02:57 AM
  #50  
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Originally Posted by Mackers View Post
Measured a couple I have laying about .....
FWIW - here's how standards and tolerances work for things like seatposts

Posts are the nominal or a bit under, while the tubes they fit are the nominal or a bit over.


Think of the nominal size as the double yellow down the middle of the road, and the tolerance as the width of the lanes.

As a practical matter manufacturers set their targets off the nominal for the same reason drivers don't crowd the double yellow.

Following this logic, seat tube reamers are made 0.05mm over the nominal, which is the max. limit, because over time the reamers will wear and cut undersize.

Last edited by FBinNY; 11-21-22 at 03:02 AM.
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