Thorn Cycles Forum
Technical => General Technical => Topic started by: Andybg on June 20, 2017, 05:27:16 pm
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Fortunately no damage done
Had a scary experience today. Out riding on my Nomad on a high speed technical downhill / condemned road - which we call the mountain here (I am sure Danneaux will confirm the enjoyment of cycling this road) and under heavy breaking the handlebars just collapsed forward.
I ended up over the bars and was only saved by landing face first on a front Surly rack and my chest on the bars.
Managed to bring the bike to a stop to find the front plate on the stem had snapped.
Not sure how unusual this is or something worth looking out for but worrying all the same.
The stem is circa 10 years old and the bike has covered at least 10k km since the bars were last off so a bit of a strange one.
Obviously aluminium metal fatigue in action but surprising all the same.
Managed to limp home riding gingerly on the top bar.
Any other peoples experience of this? Do you have a "life" for these type of components? Any suggestions on replacements?
I have ripped a few bars off bikes while climbing when it was the old quill stem and had a couple of bars drop with potholes when not tightened enough but this was a first for me.
Cheers
Andy
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I've seen 5,000 kms or 5 years quoted for lightweight drop handlebars. I don't generally get very lightweight ones, but have just replaced the old handlebars on my derailleur tourer as a precautionary measure (after a good deal more than 5 years and 5,000 kms). I used one of my alloy drop handlebars for about 53,000 kms, but I don't think I would risk this nowadays.
I have done similar distances with quill stems, up to 43,000 kms and (touch wood) no failures yet. I nonetheless intend replacing all the old alloy quill stems on the family bikes in the next few months, so long as I can find suitable replacements. I'll be leaving the old steel quill stems on the bikes that have these, as I reckon steel is much less likely to fail.
I'm not so happy with Ahead type stems, as to me the face plates and screws look flimsier. So far, I haven't done any great distances with these, but I think I would prefer to replace at intervals, or maybe try and find steel stems instead of alloy.
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I have never heard of such a failure.
If the bar is smaller than the size of stem, for example a 25.4 mm bar in a 26 mm stem, I could see how that weaken it. One of my bikes has a 25.4 mm bar and a 26 mm stem, but I used a shim. (I actually used three shims, I measured the thickness of a beer can and found I required three layers to get the correct shim thickness.)
I try to only use the stems that have four bolts, not two on the face plate. I do not know if they are stronger or not, probably not after looking where your plate broke. I had problems getting them tight enough when I used the two plate variety.
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I have never heard of such a failure.
I have seen a half dozen such failures now, all caused by running 25.4mm OD handlebars in 26.0mm ID stems. That 0.6mm is enough to overstress the clamp (the stem itself doesn't fail because there is more metal behind it) when it develops microfractures as it is tightened to a smaller radii. Under a 30x microscope, I have seen these microfractures in my "autopsies" After. They are worse if the stem face clamp is anodized, because the anodizing amounts to a hard shell, sort of like a case-hardening, that is more brittle than the softer unanodized alumunum beneath. The center of the clamp is not only generally thinnest (due to the forging or casting process of that part...in your case, reinforced in the middle but a stress riser on each side) but also under great stress if there is a mismatch.
Like George (mickeg), I prefer to use stems with 4-bolt faceplates. They provide more even clamping and a bit of a safety margin in case of fracture -- the bars would likely still remain attached to one of the clamps. If you use a 4-bolt stem, be sure to torque the fasteners to spec in a cross pattern and -- yes -- use a torque wrench. If the 4-bolt design is clamped unevenly, it loses any advantage over the 2-bolt version.
I always check my stem clamp and handlebar clamp diameters with a digital micrometer. Sometimes, even parts marked to match have enough variance to prevent full, even clamping. When I find that sort of mismatch, I return either part in search of a better match or simply shrug and put away the part with greater variance in the hope I'll find a better match someday. I have also milled 25.4mm ID stems (in my case Sakae Ringyo Super Apex quill) to match the OD of 26.0 handlebar clamps (Nitto B136). No problems (with 45,000+km on one bike) so long as the milling is concentric and true.
Yes, Andy...I do know that hill(!) :o and you were lucky to get out of it as you did, uninjured. You have excellent riding form and are a skilled rider and I think -- especially on that road, on that hill, with that sort of failure -- you can thank those skills in large part for your recovery and avoiding a full-on spill. Well done! So glad you weren't hurt, as a spill there would not be good!
All the best,
Dan.
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Yikes
That's bad.
I've only ever heard of it when counterfeit goods have been sold in place of the genuine article.
Not that I am suggesting this is the case.
There was a consumer programme on TV highlighting this issue.
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I have not measured either but my gut feeling is that the issue is 26mm stem vs 25.4mm bars. To be honest I would not have even thought to check.
I will measure tomorrow and then start looking for a replacement.
To be honest I am just glad to be alive.
Andy
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To be honest I am just glad to be alive.
Understatement of the year, especially given where it happened.
We're real glad you're still here, Andy.
All the best,
Dan.
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First I was going to dispute what Dan has said, not based on experience mind you, but based on classwork, but then I realized that I had the wrong way of it. I thought that was the back of a clamp somehow. It shouldn't fail there. Now realizing my mistake, theory lines up with exactly what Dan is suggesting.
But to put another theory into play here, I think that being too loose and not tightened enough may also be responsible as much as the too tight. Or perhaps a bad casting just waiting for it's day. In any case that is amazing (in a horrid way) how so much metal had to reach past it's tensile strength, or fatigue point. Makes me think that Steel parts are as "real" as steel frames when the fates align against us.
And in the spirit of the beer glass being 1/5th full - that certainly is an effective way to make a ride memorable! I prefer photographs myself, but to each his own. ;)
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An additional thought that probably does not apply in Andy's case above...
I have seen a number of stems clamped unevenly. What people seem to do to get there is tighten the upper /or/ lower stem bolts till they meet resistance, then start on the other ones. This almost always results in an uneven gap and uneven stresses on the clamp, bolts, and handlebars. Worse, though the fasteners may be tight, the clamp cannot exert even pressure so actual clamping can be less than desired, resulting in unexpected handlebar rotation when extra stresses are added (i.e. going through a pothole or standing while pedaling and putting more weight on the brake hoods).
It is best to tighten clamp bolts evenly in increments and then check periodically to make sure the gap between faceplate clamp and stem is even top and bottom. This ensures the clamp is square to the stem and stresses are distributed evenly. It also ensures the bolts are not angled in their bores, so there is less stress on the threads as well. I have seen stem faceplate clamp *bolts* shear from such uneven pressure.
Just a thought to keep in mind.
Best,
Dan.
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And my next bars are going to be cro-moly, not heat treated aluminum. I was feeling like I was behind the times, on the wrong side of every back-packing ideal and was torn about the perfect handlebar, now that I've found them in a Rohloff friendly version, as to whether to go with my normal or the new fangled "light weight" option.
Andy's experience here made me see the light, with respect to light-weight.
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Pavel,
Day before yesterday was disappointing for me. I parked one of my bikes on the back patio and went inside the house for a few minutes. When I returned, the bike had fallen off its (very stable) stand and was laying on its side, torn-out cat hair all 'round it. It appears the feral kitties (neighbors' doing, bane of my existence) had gotten into a fight and knocked it over.
The damage was horrendous for such a simple thing -- bent and scraped Tubus Cargo Evo (just attached!), scraped pedal and Dura-Ace bar-con pod, a divot out of the Brooks B.17 and a sligthly bent cantle plate and...the left drop of the handlebars has been bent inward about 4mm.
I don't mess with bent aluminum handlebars, especially heat-treated ones. This set will be retired and I have new ones on order. I won't ride the bike with these...it goes beyond my risk valence to do so (with past closed-head injuries and a history of multiple concussions, I don't have much margin myself).
I have a set of steel drops...22.2mm OD with 25.4mm shims. They overlap and come apart so a standard Rohloff shifter can be fitted. I'd considered selling them on, but now...
All the best,
Dan.
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Dan, on a completely off topic note ... any chance of the forum being modified so that we have a "like" button, or perhaps a ratings system on a per post basis, such as the one Neil Gunton uses on crazyguyonabike?
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Sorry to hear of the accident Andy, glad you are ok. Ive never heard of that failure so thanks for the warning.
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Glad you are ok Andy.
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To be honest I am just glad to be alive.
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I had a bad crash in May 2012. After two shoulder surgeries, I think my last physical therapy session was in April 2015 or so, almost three years later.
You are very fortunate.
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Day before yesterday was disappointing for me. I parked one of my bikes on the back patio and went inside the house for a few minutes. When I returned, the bike had fallen off its (very stable) stand and was laying on its side, torn-out cat hair all 'round it. It appears the feral kitties (neighbors' doing, bane of my existence) had gotten into a fight and knocked it over.
The damage was horrendous for such a simple thing -- bent and scraped Tubus Cargo Evo (just attached!), scraped pedal and Dura-Ace bar-con pod, a divot out of the Brooks B.17 and a sligthly bent cantle plate and...the left drop of the handlebars has been bent inward about 4mm.
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An expedition bike is supposed to look like it has traveled somewhere. Or, was this not your Nomad?
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I have a set of steel drops...22.2mm OD with 25.4mm shims. They overlap and come apart so a standard Rohloff shifter can be fitted. I'd considered selling them on, but now...
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I would consider such bars if I was starting over to build up my Nomad. Getting my regular drop bars to fit in an S&S case is not easy with the frame pieces, fork and both wheels. Split-able bars would certainly simplify things. I have had to loosen the brake levers and turn them on the bars.
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An expedition bike is supposed to look like it has traveled somewhere. Or, was this not your Nomad?
Comforting words, George, and largely in agreement, but if it had been the Nomad I would have come unhinged. "Fortunately", this was an old MTB I rehabbed into a lighter-weight Adventure bike and gravel grinder. I got the frame from a pawn shop and it was ehm, "cosmetically challenged". The rest of my bikes look as new, even the 47 year-old Raleigh Grand Sports.
I had a bad crash in May 2012. After two shoulder surgeries, I think my last physical therapy session was in April 2015 or so, almost three years later.g
You are very fortunate.
Boy, I'll say! Looking back at what Andy wrote, I fear the outcome was worse than he said...
I ended up over the bars and was only saved by landing face first on a front Surly rack and my chest on the bars.
:'( This can't be good, Andy. Are you okay? I can't imagine you got through that unscathed. I know you are a Brave Soldier (and have seen it myself), but I fear this left you the worse for wear. All healing thoughts your way.
All the best,
Dan.
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Andy ... I recommend Pub therapy. Get thee some medicine, right away!
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Thanks for the concern Dan.
All things considered I got off very lightly. My chest is a bit tender this morning where it hit the bars but nothing serious. The worst bit of damage I have done to myself is gashed my bum quite badly where I have slid off the front of the B17 saddle. That will teach me not to clench so much lol.
I am relieved that there is a reason for the failure, rather than it being one of those things that just happen. This way I can rebuild it with the right parts and forget about it.
I had been toying with the idea of removing the front rack - It is seriously heavy and rarely gets used. It will now be staying.
Cheers
Andy
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<Whew!>
Thanks so much for the update, Andy. Very glad things weren't worse. All healing thoughts your way!
Yes, that front rack surely came in handy!
All the best,
Dan.
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I think I would be happier with a steel stem, at least for my "touring" Raven Tour.
Found this link:
http://www.kinetics-online.co.uk/framebuilding/custom-stems/
A bit pricey, but should have a service life of decades.
If the builder can make a quill stem version, it would be an option for my old derailleur touring bike. With a custom stem I could fit modern handlebars that have a larger diameter centre bulge - 25.4 diameter are getting harder to find and the shape and width options are limited.
I have had steel bars and stem on my old 650B utility bike for many years, the stem is fairly basic so quite heavy. The straight bars are made from lightweight Tange Prestige tubing and not much heavier than their equivalent in aluminium, they also seem a bit more comfortable.
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I think I would be happier with a steel stem, at least for my "touring" Raven Tour....A bit pricey, but should have a service life of decades.
<nods> For sure. You're right about weight, too; a steel stem fabricated from good tubing is not so heavy compared to many aluminum offerings.
I made my own adjustable stoker stem for my tandem using cro-moly tubing, using TiG welding and fillet brazing for the joins. It is actually the portion that clamps doubly to the captain's seatpost. A quill stem sleeves into it and is held by its own wedge expander plus two clamp bolts in bosses. It has worked well for more than two decades and doesn't twist in its mounts yet is quickly and easily adjustable for the reach of various stokers.
Similarly, I made the hinged handlebar mast for my Folder from cro-moly tubing as well. It incorporates an elastomer to provide limited front suspension. Every time the bike folds, the handlebar clamp is released or tightened to hold the 'bars in place. Though I could have milled the part from aluminum billet, I felt much better fabricating it from steel in light of the expected flex cycles.
Steel is just so...reliable...and has such nice riding characteristics; steel is indeed very "real". ;)
Best,
Dan.
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Or, Titanium. Who knows, you might win the lottery tomorrow. Just what you need for your travel bike.
http://zinncycles.com/Zinn/components/travel-stems/
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Yeah! I've seen those, George. Nice they keep the handlebar alignment and much quicker than removing and retorquing 2-4 cover plate bolts.
Best,
Dan.