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Chris James.
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May 29, 2014 at 4:15 pm #21562
SideBurn
Riding home after a late shift at silly o’clock in the morning there was a loud bang; it was all I could do not to go over the front of the bike. It was dark and I had no idea what had happened. More to the point I was doing 30mph downhill. The bike swerved right, I hit the tarmac scraped down the road on my back, off the side of the road down an embankment and into a tree….. a downhill skier could not have done it any better 10 out of 10 for style =D>
Once I had checked all my body parts were in the correct place, I looked at my bike….
It appears that one of the two bolts holding the bars to the stem had snapped. The second bolt ripped out causing the handlebars to become detached…..
Luckily I had some electrical tape in my bag, I re-attached the bars and rode home B-)
Looking at the stem…. two bolts???? What was I thinking????? What a s**t design…. X(
Maybe I am being a bit harsh; I have had this stem for some time and I have used it on unforgiving territory, or British roads as they are also known.
Anyway; I have skin missing on my face, shoulder, hip and knee along with very colourful bruises on both of my thighs. Not forgetting the general aches and pains….. I am feeling very sorry for myself 🙁
I am writing this just to warn others to look very critically at their stem and ask yourself is it fit for purpose?
This incident could have been so much worse…. -
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glynr36 wrote:MKultra
glynr36 wrote:MKultra wrote:
The fact that you have manged to write 5 paragraphs defending the gross over complication of a simple mechanical task that the non-cack handed among us can do with their eyes shut just proves me right.Over complication? Its the way it should be done properly.
And you say non-cack handed, how do you know your bolts are in the right torque range, suggests a lack of engineering knowledge…I hesitate to get involved in this ‘ahem’ discussion, but from a personal point of view I have been cycling for around 30 years, doing all my home mechanicing. I have never used a torque wrench on any of my fasteners (I only have steel and alloy frames and parts though).
I have never had a fastener or component fail through over or under tightening in that time. That doesn’t mean that I think torque wrenches are useless, just that I haven’t got one and have never felt the need to buy one.
I have a degree in Mechanical Engineering, and have worked for the last 20 years in various engineering and quality roles in the aerospace industry. The last 11 of which in the field of fastener production and distribution!
On a pedantic note, there are very few ‘bolts’ on a bike. they are mostly screws! :B
gmac101 wrote:Fatigue needs
gmac101 wrote:Fatigue needs two things to do damage to a structure:1/ repeated cyclical stress
2/ a stress concentrationSo if an item is unused it won’t fatigue, it might corrode, but it won’t fatigue.
So time limits set by manufacturers are probably based on moderately heavy usage to suit their insurers. Stress cycles close to the failure load of the structure cause a lot more fatigue damage than smaller loads so they probably make adverse assumptions regarding rider weight and road smoothness.
Stress concentrations can come from 3 sources – Poor design, manufacturing defects and corrosion. Poor design is pretty rare these days as the risks are well known. Many fatigue failures result from manufacturing defects, and these mostly come from welds, getting a weld right is not a trivial task and all kinds of defects can lurk unseen in the body of a weld and these defects will often be in the form of cracks which generate stress concentrations at their tips and you get fatigue. Castings reduce the risk of defects but a poorly executed cast can also contain defects, if you are looking with suspicion at your stem following this conversation the manufacturing process with probably the smallest risk of fatigue is forging – but you normally pay extra for that.
Corrosion can generate changes in profile and cause cracks so even if the corrosion has not resulted much loss of material it will increase the risk of fatigue damage.
By the way I ride a bike with a welded 2 bolt stem, but it’s from a reputable manufacturer who I’m sure will have engineered the weld and have appropriate QA procedures that will significantly reduce the risk of a defect that’s likely to result in fatigue damage
So the mistake I made was to purchase AND use the stem?
And are you saying ITM are not a reputable manufacturer? Controversial…..gmac101
Fatigue needs two things to
Fatigue needs two things to do damage to a structure:1/ repeated cyclical stress
2/ a stress concentrationSo if an item is unused it won’t fatigue, it might corrode, but it won’t fatigue.
So time limits set by manufacturers are probably based on moderately heavy usage to suit their insurers. Stress cycles close to the failure load of the structure cause a lot more fatigue damage than smaller loads so they probably make adverse assumptions regarding rider weight and road smoothness.
Stress concentrations can come from 3 sources – Poor design, manufacturing defects and corrosion. Poor design is pretty rare these days as the risks are well known. Many fatigue failures result from manufacturing defects, and these mostly come from welds, getting a weld right is not a trivial task and all kinds of defects can lurk unseen in the body of a weld and these defects will often be in the form of cracks which generate stress concentrations at their tips and you get fatigue. Castings reduce the risk of defects but a poorly executed cast can also contain defects, if you are looking with suspicion at your stem following this conversation the manufacturing process with probably the smallest risk of fatigue is forging – but you normally pay extra for that.
Corrosion can generate changes in profile and cause cracks so even if the corrosion has not resulted much loss of material it will increase the risk of fatigue damage.
By the way I ride a bike with a welded 2 bolt stem, but it’s from a reputable manufacturer who I’m sure will have engineered the weld and have appropriate QA procedures that will significantly reduce the risk of a defect that’s likely to result in fatigue damageGordy748
I started building custom
I started building custom wheels recently so have learned a thing or two about liability, as well as real shelf life of bicycle components.All the bits on your bike fall somewhere on the weight/ durability spectrum. Older stuff, like quill stems, were very durable, but the industry ceded durability for weight in the 90s. These days you can buy a bike for not a lot that’s half the weight of Bernard Hinault’s bike, but I can guarantee it won’t last as long when subjected to the same use/ abuse.
Stems are much the same as spokes (and anything else); they have a certain number of cycles they can tolerate before failure. 10 years for an alloy stem may be a long time, but it’s more dependent on the use you’ve put it through in that time.
2 years for a stem is legally right; almost all people will not put a stem through enough abuse for it to fail in that time. Beyond that and it becomes a matter of rider weight/ road quality/ weather exposure. Chances are a stem will last a decade if ridden on smooth roads by a light rider on sunny days, but from a liability perspective you can’t guarantee that and so have to mandate a shorter shelf life, so you don’t get sued if your product eventually fails and causes an accident.
surly_by_name
surly_by_name wrote:youngoldbloke wrote:Does ANYONE do this? 5000 kms? !!!Designed to allow manufacturers to avoid liability. Hard to know if it would work (how would you ascertain whether distance had in fact been reached) and not – so far as I am aware – tested, but I imagine they’d try it on (or their insurers would).
I have got one of those bikes that are 30 years+ old (honest :^o ) but where I have changed everything on it at least once. The last thing I changed was the aluminium bars; they are now hanging on my wall B-)
Along with an ITM stem 🙁
Great discussion going onMKultra wrote:glynr36
MKultra wrote:glynr36 wrote:MKultra wrote:
The fact that you have manged to write 5 paragraphs defending the gross over complication of a simple mechanical task that the non-cack handed among us can do with their eyes shut just proves me right.Over complication? Its the way it should be done properly.
And you say non-cack handed, how do you know your bolts are in the right torque range, suggests a lack of engineering knowledge…
A torque wrench is only as good as it’s last re calibration. Some components such as very proprietary lightweight ally or carbon indeed need one, getting all sniffy about them though is just stupid. A bike is not just a high maintenance toy for sportive use, it needs to be reliable day in day out and often on tour so it needs to be repairable in the field with simple tools.A torque wrench is not one of them and components that only function within a narrow range of torque are not fit for purpose IMHO.
Well if you don’t like torque wrenches you could always count turns. In increasing order of accuracy methods of tensioning bolts are:
1: Experienced Mechanic
2: Torque Wrench
3: Counting Turns
4: Tension Indicating washers
5: Bolt tensioning equipment.Counting turns does however mean having accurate measurements of the joint, knowing the thread pitch and the mechanical properties of the materials so you work out the geometry change you need to induce the correct tension.
You are right of course that the increasing number of torque markings on your average bike is an indication that the gap between the load required to make the joint work and the load that would result in the failure of one or more components is decreasing and you have to wonder given the inherent inaccuracy in the measurement method used if it’s the right direction to go in.
surly_by_name
youngoldbloke wrote:Does
youngoldbloke wrote:Does ANYONE do this? 5000 kms? !!!Designed to allow manufacturers to avoid liability. Hard to know if it would work (how would you ascertain whether distance had in fact been reached) and not – so far as I am aware – tested, but I imagine they’d try it on (or their insurers would).
MKultra wrote:The fact that
The fact that you have manged to write 5 paragraphs defending the gross over complication of a simple mechanical task that the non-cack handed among us can do with their eyes shut just proves me right.[/quote]MKultra wrote:I wasn’t defending anything. I just thought I should make some some attempt at polite conversation to soften the conclusion (i.e., you are an idiot). Also, I like the sound of my own voice. This is a failing I am working on. But you are still an idiot.
youngoldbloke
– coincidentally was checking
– coincidentally was checking out stems on Rose’s website earlier today and came across the following advice:
“For your safety, please change aluminium stems and handlebars after two years or 5000 km at the latest. After a fall you should change these parts immediately.”
Does ANYONE do this? 5000 kms? !!!MKultra
glynr36 wrote:MKultra
glynr36 wrote:MKultra wrote:
The fact that you have manged to write 5 paragraphs defending the gross over complication of a simple mechanical task that the non-cack handed among us can do with their eyes shut just proves me right.Over complication? Its the way it should be done properly.
And you say non-cack handed, how do you know your bolts are in the right torque range, suggests a lack of engineering knowledge…
A torque wrench is only as good as it’s last re calibration. Some components such as very proprietary lightweight ally or carbon indeed need one, getting all sniffy about them though is just stupid. A bike is not just a high maintenance toy for sportive use, it needs to be reliable day in day out and often on tour so it needs to be repairable in the field with simple tools.A torque wrench is not one of them and components that only function within a narrow range of torque are not fit for purpose IMHO.
PaulBox
The only time I’ve ever
The only time I’ve ever sheared a bolt head was when using a torque wrench, that was also on a stem faceplate.glynr36
MKultra wrote:
The fact thatMKultra wrote:
The fact that you have manged to write 5 paragraphs defending the gross over complication of a simple mechanical task that the non-cack handed among us can do with their eyes shut just proves me right.Over complication? Its the way it should be done properly.
And you say non-cack handed, how do you know your bolts are in the right torque range, suggests a lack of engineering knowledge…surly_by_name wrote:MKultra
The fact that you have manged to write 5 paragraphs defending the gross over complication of a simple mechanical task that the non-cack handed among us can do with their eyes shut just proves me right.surly_by_name wrote:MKultra wrote:So they were all rubbish before carbon came along and torque wrenches were needed?Piffle.
It’s the over complication of the subject/trade by middle class people with more money than sense, much like when they all thought they could retrain as plumbers back in the early noughties.
No it’s not magical but neither is throwing money about or snobbery.
My father – who I don’t think was unusual among his generation – was able to work on the engine of his car. I seem to have a vague recollection of him having the top of the cyclinders off on at least one occasion. You would open the bonnet and there were all of the mysteries of the internal combustion engine laid out in front of you (with lots of extra room to stick your head in and swear when things didn’t work as they were supposed to). The ECU in a modern vehicle (or a hybrid engine) isn’t the kind of thing you fix on your driveway on a Saturday morning.
I don’t think mechanics were rubbish before carbon came along. I think they were skilled in working with the technology they had in front of them. Technology has, I imagine you will concede, moved on a bit.
A BBB torque wrench costs c.£45. If this is too bourgeoisie for you, you can purchase a Ritchey torque key (with a 5/4/3 and T15 bit) which will let you know when you’ve reached 5nM (recommended for most stem bolts at steerer and handlebar; in fact probably about the correct torque for pretty much every bolt on a road bike you want to tighten regularly (bottle cage bolts, seat pin collar (although my Thomson collar has a ludicrously low torque setting of 2.8nM – try and get that right by hand) – not cranks or pedals) for a much more proletarian £12.
Nothing is without risk. Using a torque wrench and following manufacturers recommended torque settings is a (not particularly expensive, empirical) means of managing some of the risks inherent in working on your own bike. (Or you can manage the risk by taking your bike to a shop.) If you don’t follow manufacturers instructions and something goes wrong then its easy to lose the argument that it was partly your fault.
If you spend a lot of money on bikes and parts (particularly lightweight parts, whether in carbon or aluminium) and you don’t use a torque wrench (or you rely on a mechanic who doesn’t use a torque wrench) you are an idiot.
MKultra wrote:So they were
MKultra wrote:So they were all rubbish before carbon came along and torque wrenches were needed?Piffle.
It’s the over complication of the subject/trade by middle class people with more money than sense, much like when they all thought they could retrain as plumbers back in the early noughties.
No it’s not magical but neither is throwing money about or snobbery.
My father – who I don’t think was unusual among his generation – was able to work on the engine of his car. I seem to have a vague recollection of him having the top of the cyclinders off on at least one occasion. You would open the bonnet and there were all of the mysteries of the internal combustion engine laid out in front of you (with lots of extra room to stick your head in and swear when things didn’t work as they were supposed to). The ECU in a modern vehicle (or a hybrid engine) isn’t the kind of thing you fix on your driveway on a Saturday morning.
I don’t think mechanics were rubbish before carbon came along. I think they were skilled in working with the technology they had in front of them. Technology has, I imagine you will concede, moved on a bit.
A BBB torque wrench costs c.£45. If this is too bourgeoisie for you, you can purchase a Ritchey torque key (with a 5/4/3 and T15 bit) which will let you know when you’ve reached 5nM (recommended for most stem bolts at steerer and handlebar; in fact probably about the correct torque for pretty much every bolt on a road bike you want to tighten regularly (bottle cage bolts, seat pin collar (although my Thomson collar has a ludicrously low torque setting of 2.8nM – try and get that right by hand) – not cranks or pedals) for a much more proletarian £12.
Nothing is without risk. Using a torque wrench and following manufacturers recommended torque settings is a (not particularly expensive, empirical) means of managing some of the risks inherent in working on your own bike. (Or you can manage the risk by taking your bike to a shop.) If you don’t follow manufacturers instructions and something goes wrong then its easy to lose the argument that it was partly your fault.
If you spend a lot of money on bikes and parts (particularly lightweight parts, whether in carbon or aluminium) and you don’t use a torque wrench (or you rely on a mechanic who doesn’t use a torque wrench) you are an idiot.
surly_by_name
So they were all rubbish before carbon came along and torque wrenches were needed?surly_by_name wrote:drfabulous0 wrote:Two bolts is a poor design as you now realise, if they are not tightened evenly then one can be taking excessive force, four bolts or one are better.I’ve been a bike mechanic for many years and I have to warn you guys not to put to much faith in reccommended torque settings, it is not uncommon to do up stem bolts to the manufacturer’s specification and find that the bars will slip under a slight load. An experienced mechanic can not only make a fair estimate of torque without the torque wrench but can also feel when the bolts are under sufficient but not excess tension.
Two bolts no worse than 4: http://www.eastoncycling.com/bike/wp-content/uploads/2010/04/RD-06-2Bolts.pdf (Although now Easton have followed the fashion to 4 bolts, suspect you can’t find this paper so easily on their website anymore.)
The bigger problem is not a faceplate that is too loose at recommended torque settings but one that is overtightened by someone who doesn’t have the benefit of a torque wrench.
And the bit about “experienced” mechanics being magical – leaving aside the fact that this is a fairy tale, a mechanic who doesn’t own/use a torque wrench doesn’t deserve the sobriquet “experienced”.
Piffle.
It’s the over complication of the subject/trade by middle class people with more money than sense, much like when they all thought they could retrain as plumbers back in the early noughties.
No it’s not magical but neither is throwing money about or snobbery.
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