What seatclamp size?

[RodTi]

Hello All,

 

What seatclamp size do 27.2mm seatpost bikes use? Is it the 28.6mm?

 

The old frame I'm using takes a 27.0mm seatpost - which has me wondering about whether or not a 28.6mm would do the job?

 

Any opinions/comments would be appreciated.

Edited January 11, 2011 by RodTi

[The Drongo]

Hello All,

 

What seatclamp size do 27.2mm seatpost bikes use? Is it the 28.6mm?

 

The old frame I'm using takes a 27.0mm seatpost - which has me wondering about whether or not a 28.6mm would do the job?

 

Any opinions/comments would be appreciated.

 

You'r testing the Tau'ri aren't you !?!?

[RodTi]

You'r testing the Tau'ri aren't you !?!?

 

Qe?

[The Drongo]

Qe?

 

"Excreta Tau'ri cerebrum vincit" ?? - Oh never mind.

 

Lets think about this RodTi.

 

You can not clamp something BIGGER with something SMALLER unless you force it.

 

A 27.2 SEATPOST will take a clamp marked 31.8 diameter.

 

27.2 + seattube wall thickness + wriggleroom.

 

COOL? Or have I just been had?

[RodTi]

"Excreta Tau'ri cerebrum vincit" ?? - Oh never mind.

 

Lets think about this RodTi.

 

You can not clamp something BIGGER with something SMALLER unless you force it.

 

A 27.2 SEATPOST will take a clamp marked 31.8 diameter.

 

27.2 + seattube wall thickness + wriggleroom.

 

COOL? Or have I just been had?

 

Drongo - you have a rather peculiar way of getting your thoughts across, but given the nature of the internet, I shall give you the benefit of the doubt.

 

As for references to "tauri", which was not, presumably, some reference to the Stargate series [c/o "Tau'ri"], well - let's just say you made as much sense as my signature, which is plainly terrible Latin.

 

Regardless - whereas I would like to suggest that you assisted me in clarifying the terribly difficult concept of something bigger needing to clamp over something smaller, I must add that this concept, surprisingly, had popped into my head, albeit briefly, all by iteslf.

 

But since I'm maybe not being clear enough - allow me to clarify:

 

I've never bought a seatpost clamp before.

Having always had an unusual seatpost size - I've never bothered to check what clampsize is regarded 'standard' for a 27.2mm post. A bit of googling now suggests that whereas many take a 31.8, it pretty much depends on the frame in question. Some even take a 30mm.

And in a few cases, a 28.6mm has worked on a 26.8 post, and at a push, on a 27.0mm post.

 

Since mine is old-skool titanium, and since most LBS's only stock the standard sizes, I was hoping that a few Hubbers might pop out of the woodwork who are making using of something other than a 31.8mm on a 27.2mm... Or, although extremely unlikely, someone who has a 27.0mm, might share what they use...

 

So in light of the above - and to get the ball rolling (or not), what post do you have, and what clamp do you use??

[The Drongo]

Drongo - you have a rather peculiar way of getting your thoughts across, but given the nature of the internet, I shall give you the benefit of the doubt.

 

As for references to "tauri", which was not, presumably, some reference to the Stargate series [c/o "Tau'ri"], well - let's just say you made as much sense as my signature, which is plainly terrible Latin.

 

Regardless - whereas I would like to suggest that you assisted me in clarifying the terribly difficult concept of something bigger needing to clamp over something smaller, I must add that this concept, surprisingly, had popped into my head, albeit briefly, all by iteslf.

 

But since I'm maybe not being clear enough - allow me to clarify:

 

I've never bought a seatpost clamp before.

Having always had an unusual seatpost size - I've never bothered to check what clampsize is regarded 'standard' for a 27.2mm post. A bit of googling now suggests that whereas many take a 31.8, it pretty much depends on the frame in question. Some even take a 30mm.

And in a few cases, a 28.6mm has worked on a 26.8 post, and at a push, on a 27.0mm post.

 

Since mine is old-skool titanium, and since most LBS's only stock the standard sizes, I was hoping that a few Hubbers might pop out of the woodwork who are making using of something other than a 31.8mm on a 27.2mm... Or, although extremely unlikely, someone who has a 27.0mm, might share what they use...

 

So in light of the above - and to get the ball rolling (or not), what post do you have, and what clamp do you use??

 

 

RodTi

 

I think no differently in real time than I do in Cyber space. I just notice more in one and less in the other.

 

You are right on all counts regarding your Latin. And, yes, I was referring to none other than the Stargate ! (exciting stuff)

To clarify, I loosely understood your signature to read that: More Superior Beings are tormenting Men of Earth, in order that we are forced to use our brains to overcome.

 

But enough of that.

 

I have an aluminium hardtail that takes a 27.2 post. The wall thickness of the tubing is just under 2.3mm. The ID of the seat tube is 27.209. The OD of the tube is 31.8

From an engineering perspective, placing a 28.6mm OD tube into a 27mm ID tube and then clamping it at a point will then place the greater stress on that point, instead of distributing it along the length of the inserted seatpost.

You are right with respect to the OD of the seat tube varying, as it will from aluminium, through steel/titanium to carbon (carbon should have a sleeve insert).

The best (safest) method is to vernier all measures and fit accordingly. Nothing should 'drop' in/on. It should have to be wiggled in/on lightly.

Your seatpost takes a tremendous amount of force. Under or oversizing anything here is likely to lead to failure.

What is the OD of the frame at the clamp point? (some tubes are tapered at that point!)

 

Lets roll! And hope that someone more sensible can shed greater light on this matter.

[javadude]

Crumbs Drongo, you have a weird way of getting your point across. Older steel frames have seat tube diameters of 28.6 for posts sized 27.2 and smaller, so RodTi's question is pretty valid.

 

Is it possible that his titanium frame that has a 27.0 seatpost requires a 28.6 seatpost clamp? I'm personally not sure, since most steel frames of that size have brazed on seatclamps and I've yet to come across a 28.6 clamp.

[The Drongo]

Crumbs Drongo, you have a weird way of getting your point across. Older steel frames have seat tube diameters of 28.6 for posts sized 27.2 and smaller, so RodTi's question is pretty valid.

 

Is it possible that his titanium frame that has a 27.0 seatpost requires a 28.6 seatpost clamp? I'm personally not sure, since most steel frames of that size have brazed on seatclamps and I've yet to come across a 28.6 clamp.

 

I do not intend to cause alarm velo.

 

I have also asked the good gent what size OD his frames seatstay is. The clamp size makes reference to the ID of the clamps collar-seat itself therefore it would appear to be physically impossible to clamp a 27.0 seatpost using a 28.6 clamp.

 

These are the COMMON seatpost clamp sizes: 28.6mm (1 1/8"), 30mm, 31.8mm (1 1/4"), and 34.9mm (1 3/8").

A brazed or built in clamp is, well it's built in, so I am not sure that this is RodTi's implication, but it is a point well taken.

 

If he has a Ti frame, he may well require a 30.6 OR a 34.9 clamp if his seatpost is a 27.2, it all depends on the wall thickness of the Ti.

[RodTi]

RodTi

 

I think no differently in real time than I do in Cyber space. I just notice more in one and less in the other.

 

You are right on all counts regarding your Latin. And, yes, I was referring to none other than the Stargate ! (exciting stuff)

To clarify, I loosely understood your signature to read that: More Superior Beings are tormenting Men of Earth, in order that we are forced to use our brains to overcome.

 

But enough of that.

 

I have an aluminium hardtail that takes a 27.2 post. The wall thickness of the tubing is just under 2.3mm. The ID of the seat tube is 27.209. The OD of the tube is 31.8

From an engineering perspective, placing a 28.6mm OD tube into a 27mm ID tube and then clamping it at a point will then place the greater stress on that point, instead of distributing it along the length of the inserted seatpost.

You are right with respect to the OD of the seat tube varying, as it will from aluminium, through steel/titanium to carbon (carbon should have a sleeve insert).

The best (safest) method is to vernier all measures and fit accordingly. Nothing should 'drop' in/on. It should have to be wiggled in/on lightly.

Your seatpost takes a tremendous amount of force. Under or oversizing anything here is likely to lead to failure.

What is the OD of the frame at the clamp point? (some tubes are tapered at that point!)

 

Lets roll! And hope that someone more sensible can shed greater light on this matter.

 

 

 

"From an engineering perspective..."? This being your chosen field? You make more sense now!

[RodTi]

Crumbs Drongo, you have a weird way of getting your point across. Older steel frames have seat tube diameters of 28.6 for posts sized 27.2 and smaller, so RodTi's question is pretty valid. Is it possible that his titanium frame that has a 27.0 seatpost requires a 28.6 seatpost clamp? I'm personally not sure, since most steel frames of that size have brazed on seatclamps and I've yet to come across a 28.6 clamp.

 

 

I do not intend to cause alarm velo. :)I have also asked the good gent what size OD his frames seatstay is. The clamp size makes reference to the ID of the clamps collar-seat itself therefore it would appear to be physically impossible to clamp a 27.0 seatpost using a 28.6 clamp.These are the COMMON seatpost clamp sizes: 28.6mm (1 1/8"), 30mm, 31.8mm (1 1/4"), and 34.9mm (1 3/8").A brazed or built in clamp is, well it's built in, so I am not sure that this is RodTi's implication, but it is a point well taken.If he has a Ti frame, he may well require a 30.6 OR a 34.9 clamp if his seatpost is a 27.2, it all depends on the wall thickness of the Ti.

 

 

Thanks Velo and Drongo...

 

I guess the only proper way to go about this, would be to get the diameter measured?

 

I never thought about checking the FD clamp - the tube is ovalised towards the BB, but since I managed to get (what I presume to be??) a stock standard 2007 XTR bottom clamp FD on, then the ovalisation (is that even a word?) occurs lower than where it is clamped... Will try and figure that out.

 

The problem I'm faced with is that I don't have all that much readily available information pertaining to the frame, given it's age - and it's no longer a frame that too many people have... I'll also try my luck contacting owners on forums that I came across overseas...

 

I was tempted to take it into the LBS, and try out different sizes - but now question whether this will be any use, since it's probably unlikely I'll get one that would fit perfectly... I guess it would help in me working out what doesn't fit! In any event - the LBS might have 3 different sizes (at most), and are probably not going to be willing to order an unusual size, only for it not too fit...

 

Any idea what type of business would have calipers of this nature to do the measurements??

[Zaskar]

Maybe this will help?

Edited January 11, 2011 by Zaskar

[Zaskar]

Sorry only saw now that you are looking for 27.0, and not 27.2

 

What frame is it for?

Edited January 11, 2011 by Zaskar

[The Drongo]

Thanks Velo and Drongo...

 

I guess the only proper way to go about this, would be to get the diameter measured?

 

I never thought about checking the FD clamp - the tube is ovalised towards the BB, but since I managed to get (what I presume to be??) a stock standard 2007 XTR bottom clamp FD on, then the ovalisation (is that even a word?) occurs lower than where it is clamped... Will try and figure that out.

 

The problem I'm faced with is that I don't have all that much readily available information pertaining to the frame, given it's age - and it's no longer a frame that too many people have... I'll also try my luck contacting owners on forums that I came across overseas...

 

I was tempted to take it into the LBS, and try out different sizes - but now question whether this will be any use, since it's probably unlikely I'll get one that would fit perfectly... I guess it would help in me working out what doesn't fit! In any event - the LBS might have 3 different sizes (at most), and are probably not going to be willing to order an unusual size, only for it not too fit...

 

Any idea what type of business would have calipers of this nature to do the measurements??

 

Ovalisation is indeed a word.

 

Here is a suggestion. Rumble your fiets on over to a MICA hardware, they seem to stock verniers, and borrow one for 1minute - no charge.

If your local MICA is less than friendly then go to the nearest spot that sells fasteners, they REALLY should have one.

 

What frame is it? (should have asked that 2 hours ago )

[RodTi]

Maybe this will help?

 

It is the current setup i have on my Rocky Mountain Vertex Team frame. The same post / clamp combo also works on Amateurs Cannondale F400 frame.

 

Thanks Zaskar...

 

I honestly don't know if it does?

 

I've got a Thomson Elite inline 410mm as well, only mine's a 27.0mm... I had a 26,8mm in before - and experienced slippage. Did all the research, and confirmed it was a 27.0mm - duly bought it, only to find it was too big!!

 

Had to take sandpaper to it, and took off the paint all along the bottom half of the post - now it fits tight as a tiger...

 

The current clamp is an old GT one, with no markings on it to indicate size. I guess I could simply take the clamp along to LBS's, and gauge its size as against others - but with us now talking about millimeters, don't really trust my eyes!

 

As is clear from your pic - there's quite a bit of a gap between the 27.2 post and the 31.8 clamp... And as stated by Drongo, this is the wriggle space for the frame... With my frame being Ti, and being old-skool at that, I'm not really sure how it would compare, width-wise, to other frames - which brings me back to square one...

 

Anyone know of Cape Town/Paarl/Stellenbosch/Durbanville LBS's who might have the proper measurement devices - or would I be able to get something similar at an engineering firm/vehicle repair/mechanic shop??

[The Drongo]

Maybe this will help?

 

Cool pic Zaskar.

 

Thats a KCNC bolt on, but they only appear to do the standard sizes.

 

I seem to recall SALSA bikes had a range of bolt-on and levered clamps. Not sure if there is an SA agent though. Might have to buy off the web.

[javadude]

I do not intend to cause alarm velo.

 

The clamp size makes reference to the ID of the clamps collar-seat itself therefore it would appear to be physically impossible to clamp a 27.0 seatpost using a 28.6 clamp.

 

 

 

Why impossible? Titanium and steel tubing is less than 1mm thick, so if the titanium frame tubing is 0.8mm thick at the seat tube then it could take a 28.6 clamp.