Seat post tolerance in a frame

[Peachy!]

Guys, FFS, talk about the blind leading the blind! This is a real downside of forums, where all sorts can post irrespective of their knowledge of cycle mechanics. You end up with lots of "advice" that isn't worth a cup of cold tea, and the odd well-informed post getting lost in the noise.
No one, absolutely no one, has mentioned that simple and effective piece of kit ... A SEAT POST GAUGE. It costs about £20 from the likes of SJS and will tell you in 5 seconds what the correct seat post size is for your frame.
The seat cluster lug (assuming you have a lugged frame) or top of the seat tube (for a lugless frame) is almost never round because of heat distortion during manufacture. (Sometimes a diligent frame builder will ream it to be nicely round after building, but that's unusual.) So stick the gauge in, let it find its natural position, and read off the required set post diameter. Now you know what the correct seat post size is supposed to be. But be aware that no manufactured article is ever completely round and there are always manufacturing tolerances. This is why measuring with a Vernier is effing hopeless ... it will only measure the diameter at one point on the diameter but the bloody thing ain't round! Never mind, a decent manufacturer can be reasonably relied upon to get this more or less right. So get a seat post of reasonable quality in the nominal, measured size and get on cycling and enjoying life.
Phew!

Dude…. Breath….
(& it’s cold piss)

 

[sastusbulbas]

The GT was originally a 27.2 post, what you may have is 0.1 wear due to age, seat posts with grease and grit over the years, weight and flex etc, all adds up on an old bike. Or a missing bonded shim. Problem was, the shim was not all that deep, and if an owner ran a maxed out post height with the post not extending past the shim it would exasperate the wear. A lot of fluted seat tube designs suffer this too even without an insert, Treks 930 steel frames as an example, bang on 27.2 when new, many suffer excessive play and even crack at the brazed on seat bolt lugs or relief slot.

DEAN, Kona, and a few others who used Sandvik titanium as an example had a thin alloy bonded insert as the seam titanium tubes were not 27.2 diameter or reamable, no Sandvik titanium frame from memory was ever put out with a 27.4 diameter requirement.

Raleigh too used shims for their Dyna Tech Turus frames, but with a weird 28.0 size in the early mid 90's, luckily the X-Lite Z post was available in that size and it's anodized head matched the L168 stem, X-Lite's red annodizing was the best red, allong with Hope hubs. When X-Lite stopped making a 28.0 post that bike was fitted with a USE and shim.

I have been away from Retrobike for some time, I was sure there was places online that manufactured alloy machined inserts for old frames, with that required top step, though they still had to be bonded in with a specific resin. But a quick google search showed nothing.

Years of modern bikes and everything being carbon these days, old Titanium and Steel is a rare treat.

 

[Woz]

Well, it's certainly going to help if the top of the tube HASN'T been distorted by clamping the wrong size of post!
It's always a good idea to start out simple and assume you don't have that problem. (I think Einstein had something to say on this.) If your gauge says you need a 27.4mm seatpost and you've fitted a 27.4mm post but still have problems, then you think again.
The cure for the difficulty that you mention (top of tube distorted) is to ream the tube out to the next size down from that indicated on the gauge. (So you need the gauge.) This isn't really a job for an enthusiastic amateur as you need the seatpost reamer and a bit of facility in working with metal.
OK, so that's how a seatpost gauge is going to help.

That makes no sense whatsoever I'm afraid. If the gauge says 27.4, you suggest reaming down to 27.2

The OP stated there was already a 27.2 seat-post in the frame which he was not happy with, causing the slit to close too much.

Personally, never felt the need for a seat-post gauge, some are utter useless crap like the Icetoolz one. Just to rub it in
..... pun intended .... only a fool would buy one I've got far too many different size posts from the tip
for free that serve me well. The thing is with this hobby, pretty much every retro frame would be 2nd hand, and at the
mercy of ham-fisted morons, shite initial assembly to keep up with the MTB boom, thrown from a great height into a skip, etc. etc. etc.

 

[Woz]

The GT was originally a 27.2 post, what you may have is 0.1 wear due to age, seat posts with grease and grit over the years, weight and flex etc, all adds up on an old bike. Or a missing bonded shim. Problem was, the shim was not all that deep, and if an owner ran a maxed out post height with the post not extending past the shim it would exasperate the wear. A lot of fluted seat tube designs suffer this too even without an insert, Treks 930 steel frames as an example, bang on 27.2 when new, many suffer excessive play and even crack at the brazed on seat bolt lugs or relief slot.

DEAN, Kona, and a few others who used Sandvik titanium as an example had a thin alloy bonded insert as the seam titanium tubes were not 27.2 diameter or reamable, no Sandvik titanium frame from memory was ever put out with a 27.4 diameter requirement.

Raleigh too used shims for their Dyna Tech Turus frames, but with a weird 28.0 size in the early mid 90's, luckily the X-Lite Z post was available in that size and it's anodized head matched the L168 stem, X-Lite's red annodizing was the best red, allong with Hope hubs. When X-Lite stopped making a 28.0 post that bike was fitted with a USE and shim.

I have been away from Retrobike for some time, I was sure there was places online that manufactured alloy machined inserts for old frames, with that required top step, though they still had to be bonded in with a specific resin. But a quick google search showed nothing.

Years of modern bikes and everything being carbon these days, old Titanium and Steel is a rare treat.

The DBR Sandvik is 27.0 with factory inserted alloy shim, for 31.8 OD seat-tube.

I'm reasonably sure Kona's of the same period were the same.

 

[kingoffootball]

The GT was originally a 27.2 post, what you may have is 0.1 wear due to age, seat posts with grease and grit over the years, weight and flex etc, all adds up on an old bike. Or a missing bonded shim. Problem was, the shim was not all that deep, and if an owner ran a maxed out post height with the post not extending past the shim it would exasperate the wear. A lot of fluted seat tube designs suffer this too even without an insert, Treks 930 steel frames as an example, bang on 27.2 when new, many suffer excessive play and even crack at the brazed on seat bolt lugs or relief slot.

DEAN, Kona, and a few others who used Sandvik titanium as an example had a thin alloy bonded insert as the seam titanium tubes were not 27.2 diameter or reamable, no Sandvik titanium frame from memory was ever put out with a 27.4 diameter requirement.

Raleigh too used shims for their Dyna Tech Turus frames, but with a weird 28.0 size in the early mid 90's, luckily the X-Lite Z post was available in that size and it's anodized head matched the L168 stem, X-Lite's red annodizing was the best red, allong with Hope hubs. When X-Lite stopped making a 28.0 post that bike was fitted with a USE and shim.

I have been away from Retrobike for some time, I was sure there was places online that manufactured alloy machined inserts for old frames, with that required top step, though they still had to be bonded in with a specific resin. But a quick google search showed nothing.

Years of modern bikes and everything being carbon these days, old Titanium and Steel is a rare treat.

I thought the Lighning was made in Asia, rather than being a Sandvik frame or is that still open to debate?

 

[2manyoranges]

Ishaw is confronting this:

...So the 27.4 trial post arrived today and it is very tight. Fits in the top fine but the further it goes the tighter it gets, I have to push pretty hard to get it down, and I was worried it would get stuck. It could nearly be ridden without the clamp being tightened, not had a post this tight in a frame...\

Which is a worry. And I can see how challenging that is. My take? Most likely someone with more enthusiasm than understanding whacked in a too-large post into the seattube, flaring the top. Once it has flared it is well nigh impossible to reduce the diameter. I have experienced this many many times, and it is most frustrating.

If it’s just a blob of stuff from welding, then wire brushing using the specialist wire brush/reamer is good thing to check out and eliminate.

Remedies?

Get away with a Very Robust seatpost clamp and really tighten the bugger up.
Brutal and cheap.

Bite the fashion bullet and use a USE with long shim, as long as shim extends beyond seattube-toptube junction
Aesthetic compromise - about 50gbp in total. More if using ti USE.

Cut the seatpost to a length where it marginally binds but clamps properly at the top - as long as this means enough insertion. In this configuration will only ever be rideable by you or someone with same inside leg.
Cheap and will do the job.

Take the frame to a ti specialist and get a proprietary collar fitted.
Undoubtedly expensive and poor company will mess up frame.

I think that’s it - anyone else?.......

 

[sastusbulbas]

Actually yes, you are correct on the early Kona frames, but as I said, I was giving examples and I wasn't too good at wording that, if you read you will see I infer many manufactures used bonded inserts, and not that they all took 27.2 post sizes, but that the Titanium tubing frame manufacturers sourced was of too large a diameter to be reamed to 27.2 due to required outer diameter etc. 26.8, 27.0, 27.2 were the norm with bonded alloy shims as they were the most common sizes too.

My head is fuzzy as I said been away from old bikes too long, usually not too bad on seat post sizes, never remembered a 27.4 requirement on any major brands, for instance the original steel budget Kona's I remember having a smaller diameter 26.6 posts, I remember being unable to build one with a full Deore DX build as the post was not available in that budget Kona's size.

I remember some talk of Kona Ti frames suffering a similar problem, where second hand purchasers of King Kahuna were finding the 27.0 too slack simply due to wear. Were these not Sandvik tubed TST manufactured with bonded 27.0mm inserts right up to 2001?

As for the GT Lighting manufacture I wasn't actually stating it was made by Sandvik/TST , as I know it was budget compared to the Xizang that was LaVoy then Sandvik. It was made in Taiwan, and of Sandvik tubing apparently, manufactured for around 2 years.

Sandvik was a titanium tubing company, who also outsourced titanium tubing for manufacture of bicycles and various other items all over the world, and bicyles were a small niche in that portfollio, TST if I remember correctly being responsable for many a bike brands titanium bicycle frames up to 2001 and who used Sandvik, there is some history and digging to get to the bottom of it, the tubing and welding were fantastic, the welding was better than many Litespeed Ti frames in my opinion, alignment was usually spot on too.
Most of the 90's volume brand names with a Titanium model had a Sandvik tubed frame, many were identical or similar, with that trademark bullet end cap, these were not high end expensive titanium frames but middle road pricing and great products.
Put it this way, I used a Dean Titanium more than any other Titanium frame during the 90's, I preferred the DEAN's geometry to the Merlin XLM of that era.
From what I remember TST had been welding titanium longer than most other companies including Merlin and Lightspeed, I lost interest in Merlin when they changed hands in 1998, Seven was the new Merlin at that point, in 2000 when American Bicycle took over I almost went for the newer XLM due to it's geometry and disc mounts as the DEAN simply had it's day, I had been running SID 98's and found the box crown too high, retrofitting an SL crown helped, but I ended up running Pace RC31 rigids and as those were comprimising the Avid Arch Rival Supremes, then I just decided to have a break. Sold my last titanium frame on this forum many years ago, Litespeed Telico which never progressed beyond 1996 Judy SL due to the geometry, but I had preferred the DEAN even to that.

Used to be really into all this, a lot is fuzzy and possibly wrong, last time I used to frequent here I was clearing my loft of all this 90's bike stuff. Sorry if its irritating.

 

[FluffyChicken]

How long before you accidentally buy another 90s bike.

 

[old_coyote_pedaller]

Well, it's certainly going to help if the top of the tube HASN'T been distorted by clamping the wrong size of post!
It's always a good idea to start out simple and assume you don't have that problem. (I think Einstein had something to say on this.) If your gauge says you need a 27.4mm seatpost and you've fitted a 27.4mm post but still have problems, then you think again.
The cure for the difficulty that you mention (top of tube distorted) is to ream the tube out to the next size down from that indicated on the gauge. (So you need the gauge.) This isn't really a job for an enthusiastic amateur as you need the seatpost reamer and a bit of facility in working with metal.
OK, so that's how a seatpost gauge is going to help.

Please, please, please tell me how one of the seat-tube gauges you suggested can measure down past the top 20mm or so of a seat-tube?
The OP has already mentioned at least twice that he can get a seat-post to fit in but it becomes a lot tighter as it is inserted to correct length and he also says quite clearly the reason for needing to find out size is because the wrong size post seems to have been fitted and top of seat-tube IS distorted.
In your scenario you've bought the seat-post gauge, 20 quid, which tells you to get a certain size of post, more dosh, if it doesn't fit you start again, more money.

The best way to check sizes (you want to keep it simple don't you?) is what Woz suggested, try several different sizes of post that you have measured the full length of with a digital vernier caliper so that you can determine the diameter of seat-tube where post is binding down inside seat-tube which is the unknown size. I know not everyone has digital vernier calipers and loads of posts but then again you think we all should have a seat-post gauge.

 

[d8mok]

@ishaw where are you located? Is it Macclesfield or am I confusing you with another member