# Poor frame designs



## tradesecrets (7 Feb 2011)

As i haven't posted on here in a while am sure many of you have noticed a trend amongst manufacturers of which the basic frame design has alterd to such an extent in which the seat stem is angled to such a degree that it will cause your frame to snap 


Which what happend to my bike and it's an Alu frame and I have sent an email to the bike manufacturer yet heard nothing back still even though my bike is only a year old it might be a 08 model still that's no excuse in my eyes yet I've only owned the bike for a year .. 

It snapped just below the seat steam lock at an angle of 45 degrees sending me backwards lucky for me it didn't happen on a busy road with a truck or bus at my rear !!


It simply snapped because the way the frame was designed it couldn't cope with the stress of weight over a period of time and when i say that i don;t mean am a overweight person by any means i used my bike for work rest and play and for shopping ... and my bike in question is a carrera Fury


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## upsidedown (7 Feb 2011)

Being not exactly a lightweight i steer well clear of compact frames. You have to be quite careful as the quoted sizes of the top tubes and seat tubes are often effective lengths, not the actual lengths.


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## Zoiders (7 Feb 2011)

Apart from being a compact MTB frame there is nothing particulary weird or wrong with a bog standard rigid Carrera frame.

The frame geometry is well within the norm. Have you been running it with too much post showing by any chance?


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## tradesecrets (7 Feb 2011)

Zoiders said:


> Apart from being a compact MTB frame there is nothing particulary weird or wrong with a bog standard rigid Carrera frame.
> 
> The frame geometry is well within the norm. Have you been running it with too much post showing by any chance?




To be fair the fury was my 2nd carerra purchase and my previous carrera being "Absolute" model I never have or experienced any such issues ..with frame breakages


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## Zoiders (7 Feb 2011)

I am guessing you are on the heavy side?<BR><BR>Frames have been known to break, that is not however a design flaw.<BR><BR>Be carefull with saying stuff like that as it's actionable, manufacturing process faults are not the same as a design fault.


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## tradesecrets (7 Feb 2011)

am only 13st lol


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## mickle (7 Feb 2011)

Warranty.


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## Rob3rt (7 Feb 2011)

How much post was in the seat tube. Min insertion only covers the seat pin, not the frame. You need to consult the frame documentation for the amount that must be inserted into the frame. Or use a rule of thumb like, at least enough to drop below the point where the top tube joins the seat tube.


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## 2Loose (7 Feb 2011)

Rob3rt said:


> How much post was in the seat tube. Min insertion only covers the seat pin, not the frame. You need to consult the frame documentation for the amount that must be inserted into the frame. Or use a rule of thumb like, at least enough to drop below the point where the top tube joins the seat tube.



+1

If the seatpost was down below the top tube, then definitely a warranty claim, this should not happen unless something was faulty with either the welds or the materials.

If it was above the top tube...I think you may have difficulty claiming faulty anything, let alone a dodgy design.


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## peelywally (7 Feb 2011)

surely if it broke above top tube it was the wrong sized frame for rider ?




id take it back no frame should snap under normal riding conditions within that time imo


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## RecordAceFromNew (7 Feb 2011)

Folks let us take a look at a couple of Carrera Fury pics:








and now a more recent (2009 and 2010) version:








What does the new gusset plate thing above the top tube tell us?

Depending on how long the older version's seat tube is sticking up unsupported above the top tube, if it is more than an inch (which appears likely), I would certainly consider that a stupid engineering design, which presumably has since been "cured" by the gusset...


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## henshaw11 (7 Feb 2011)

>What does the new gusset plate thing above the top tube tell us?

Err...it rather depends what the rest of the tubing is round there - eg wall thicknesses and butted or not. I guess it's one way of getting more standover room rather than upping the wall thickness of the seat tube, the change doesn't necessarily indicate a design flaw.

On most seatposts the min insertion point is 100m - tho' on some it's 75 or 80mm - either way, it depends what the frame manufacturer's recommendation is. If you had less than that, then you needed a longer seatpost - you can get them up to about 430+mm (I've got posts of 400mm or more on a couple of bikes..)
I'd have thought you'd want the bottom of the seatpost to be at least a couple inches below the lower toptube weld to get much support from the seattube - 'just' under is a fair bit of difference.


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## RecordAceFromNew (8 Feb 2011)

henshaw11 said:


> >What does the new gusset plate thing above the top tube tell us?
> 
> Err...it rather depends what the rest of the tubing is round there - eg wall thicknesses and butted or not. I guess it's one way of getting more standover room rather than upping the wall thickness of the seat tube, the change doesn't necessarily indicate a design flaw.
> 
> ...



Perhaps it is semantic, but Henshaw I would welcome to be enlightened as to what purpose the unnecessarily long and unsupported version of the seat tube above the top tube serves, given by your own estimation the seat post needs to reach a couple of inches below the lower weld of the top tube? From an engineering design standpoint, imho it is an unnecessary weight at best given the leverage, load path and stress concentration caused by the seat post there, and a potentially dangerous trap for the unwary at worst.

To the OP it will indeed be important to know what exactly does the bike's instruction manual, if one was supplied by Halfords, says re seat post insertion, and if no reference where the minimum insertion mark on the supplied seat post is. I believe these frames have a two year warranty.


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## snailracer (8 Feb 2011)

RecordAceFromNew said:


> ...*what purpose* the unnecessarily long and unsupported version of the seat tube above the top tube serves, given by your own estimation the seat post needs to reach a couple of inches below the lower weld of the top tube? From an *engineering design* standpoint, imho it is an unnecessary weight at best given the leverage, load path and stress concentration caused by the seat post there, and a potentially dangerous trap for the unwary at worst...


Some reasons, just off the top of my head:
- Long seat post cushions bumps
- "Compact" geometry gives more standover clearance, and fewer frame sizes need be stocked to cover all rider sizes

IMO the added top-tube/seat tube gusset is a bodge: the top tube itself IS a gusset. After all, many bikes don't even have a top tube.


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## Zoiders (8 Feb 2011)

Well this turned into a pedant pissing contest pretty quick.<BR> <BR>Extended seat tubes are very common, a lot of frames use that feature from several big name manufacturers, breaking the seat tube at the top tube weld is common with that design if you run a seat tube with out enough insertion. <BR><BR>The gusset on the newer Carreras is just a cosmetic gimmick, you don't want more welds in that area causing more stress risers, down tube gussets that meet the the head tube are left open ended for this exact reason.<BR> <BR>So when people have quite finished trying to over intellectualise the thread to put them self forward as "experts"...  <BR><BR>


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## mickle (8 Feb 2011)

Zoiders to the rescue.


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## Zoiders (8 Feb 2011)

Well it was turning in to a load of beard stroking guff.

I was waiting for Recordace to put a jazz CD on and point at people with his pipe while talks down to them.


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## the snail (8 Feb 2011)

RecordAceFromNew said:


> What does the new gusset plate thing above the top tube tell us?
> 
> Depending on how long the older version's seat tube is sticking up unsupported above the top tube, if it is more than an inch (which appears likely), I would certainly consider that a stupid engineering design, which presumably has since been "cured" by the gusset...



+1 I doubt they would go to the expense without good reason i.e. too many warranty claims and that sort of failure could kill someone.


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## mickle (8 Feb 2011)

Zoiders said:


> Well it was turning in to a load of beard stroking guff.
> 
> I was waiting for Recordace to put a jazz CD on and point at people with his pipe while talks down to them.



Lols.


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## Zoiders (8 Feb 2011)

An extended seat tube allows you to move the seat post slot round to the front of the tube.<BR><BR>It prevents mud and water ingress.<BR><BR>Of course if some of you were were professing first hand knowledge on the subject of MTBs one of you might have known this.


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## PpPete (8 Feb 2011)

What's with <BR><BR> Zoiders? I've noticed it some of your other posts too...,. Is it some kind of engineering notation ?


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## Zoiders (8 Feb 2011)

It's the forum software having a spaz when you edit things.

BR = break when you hit return, for some reason it's not carrying out the commands.


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## mickle (8 Feb 2011)

It's a Trimfone ringing in the background of his 1970's office.


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## PpPete (8 Feb 2011)

mickle said:


> It's a Trimfone ringing in the background of his 1970's office.


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## asterix (8 Feb 2011)

Well, if you will buy frames built out of re-cycled coke tins..


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## RecordAceFromNew (8 Feb 2011)

Zoiders said:


> Well it was turning in to a load of beard stroking guff.
> 
> I was waiting for Recordace to put a jazz CD on and *point at people with his pipe while talks down to them*.






Zoiders said:


> An extended seat tube allows you to move the seat post slot round to the front of the tube.<BR><BR>It prevents mud and water ingress.<BR><BR>*Of course if some of you were were professing first hand knowledge on the subject of MTBs one of you might have known this.*


 It is funny how the pot can't help calling the kettle black, can he?


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## SteelUn (8 Feb 2011)

RecordAceFromNew said:


> It is funny how the pot can't help calling the kettle black, can he?



+1.











and he is also the one who calls other CCers trolls!


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## Zoiders (9 Feb 2011)

RecordAceFromNew said:


> It is funny how the pot can't help calling the kettle black, can he?


Get over yourself you cut and paste google merchant.


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## RecordAceFromNew (9 Feb 2011)

Zoiders said:


> Get over yourself you cut and paste google merchant.



Ahhh you are still smart from evidence not matching your wild guesses? I feel for you...


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## Zoiders (9 Feb 2011)

You find 5 speed blocks on 126 wheels.

You are going to have to accept that and move on.


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## Davidc (9 Feb 2011)

asterix said:


> Well, if you will buy frames built out of re-cycled coke tins..



Quite

Recycled baked bean tins for me, every time.


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## snailracer (10 Feb 2011)

Davidc said:


> Quite
> 
> Recycled baked bean tins for me, every time.


Coke cans are aluminium. Baked bean tins are steel. And steel is real.


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## henshaw11 (10 Feb 2011)

>Perhaps it is semantic, but Henshaw I would welcome to be enlightened as to what purpose the unnecessarily long and unsupported version of the seat tube above the top tube serves, given by your own estimation the seat post needs to reach a couple of inches below the lower weld of the top tube? From an engineering design standpoint, imho it is an unnecessary weight at best given the leverage, load path and stress concentration caused by the seat post there, and a potentially dangerous trap for the unwary at worst.


As mentioner by myself/others - more standover height, and you need some region of the seat tube to deflect 'cos you've got a clamp over it - if it were too short it might actually stress the region around the welds more (which IIRC tend to be harder too = less flex)

Unless you actually know what the tubing dimensions/characteristics etc, the fact there's a design change doesn't mean a fat lot. 

Go have at other mtb frames around - eg Specialized ,Santa Cruz- that configuration's not uncommon at all. And you do realise that many frames come from a relatively small number of manufacturers - so that if a manufacturer's tooled up for a one set of designs it may actually make more sense for someone to adopt that, rather than insist on something different.

For all I know (or equally give a toss), it could as much be a fashion statement !

Take a look at some time trial frames - more upright, but *loads* of seat tube...


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## MacB (24 Dec 2011)

Just doing a bit of thread resurrection here as I'm curious on this subject as to what are the pros and cons around seat tube/top tube interface design. Specifically extending the seat tube above the top tube and by how much.

I can see that a forward facing seatpost clamp slot would require a minimum extension to avoid the slot getting too close to the welds.

I can see that a forward facing slot could reduce gunk getting in seat tube

I can also see that it can allow for a steeper TT angle without overly reducing the amount of seat tube available for seatpost insertion.

I can see how this is helpful for frames with shaped seat tubes where a seatpost can only go down so far.

I can see how a longer extension above could require some form of additional support.

What I can't seem to find is anything concrete on the actual strengths, or pros and cons, of the various design options. Looking across manufacturers I can find a variety of clamp slot orientations, seat tube extensions above TT, additional supports and various inserts. I can even find variations across a manufacturers range or from year to year, as indicated by the Carrera changes upthread.

I do understand minimum insertion depths for seatposts and can contrast that with frame insertion requirements. I would also err to the cautious side in this area being of the larger persuasion and running a setback seatpost.

But say you wanted something pretty bombproof, not downhill/all mountain bomproof, but otherwise sound. Assuming you don't care about the slot orientation(or would prefer rear facing, think permanent mudguard/splashguard in place), would you be better to:-

1. sacrifice a bit of standover by shallowing out the TT slope and having less seat tube extension - but still retaining comfortable standover - if so what amount of extension above the TT is about right?
2. keep the TT slope but support the seat tube extension above the TT in some way - if so which way is best?
3. do a mix of both, so shallow the slope but also keep the above TT extension by increasing overall ST length, and add in some additional support for good measure.

Bike useage I'm thinking mild XC, not racing, trail and rough stuff touring, but built for tanklike durability rather than speed.


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