Poor frame designs

[tradesecrets]

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

 

[upsidedown]

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.

 

[Zoiders]

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?

 

[tradesecrets]

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

 

[Zoiders]

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.

 

[tradesecrets]

am only 13st lol

 

[mickle]

Warranty.

 

[Rob3rt]

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.

 

[2Loose]

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.

 

[peelywally]

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

 

[RecordAceFromNew]

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...

 

[henshaw11]

>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.

 

[RecordAceFromNew]

>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.

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.

 

[snailracer]

...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.

 

[Zoiders]

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>