Is slightly crimped aluminum downtube dangerous?
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Is slightly crimped aluminum downtube dangerous?
I'm working on a bike that has slight crimping or denting on both sides of the downtube. Specialized Sirrus hybrid, welded aluminum frame. I'm curious for some knowledgeable opinion on whether the bike is safe to ride. Is there meaningfully increased risk of the downtube caving in while riding? The dimpling isn't deep, and the indentation on the left is about an inch away from the one on the right.
I'm looking for your best estimate of the probable risk here, not a careful lawyer statement. I'm not looking for legal advice.
The frame otherwise appears in good shape. My best guess is the denting happened while transporting the bike with other bikes, but that's only a guess.
Note: when you reply to this, you can edit out the photos so that each reply doesn't take up a lot of vertical space. Unless you specifically want one of the images in your reply, of course.
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I'm looking for your best estimate of the probable risk here, not a careful lawyer statement. I'm not looking for legal advice.
The frame otherwise appears in good shape. My best guess is the denting happened while transporting the bike with other bikes, but that's only a guess.
Note: when you reply to this, you can edit out the photos so that each reply doesn't take up a lot of vertical space. Unless you specifically want one of the images in your reply, of course.
IMG_20180202_125411.jpg
IMG_20180202_125438.jpg
IMG_20180203_002931.jpg
IMG_20180203_002943.jpg
#2
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I'm looking for your best estimate of the probable risk here, not a careful lawyer statement. I'm not looking for legal advice.
The frame otherwise appears in good shape. My best guess is the denting happened while transporting the bike with other bikes, but that's only a guess.
That frame is toast. It would appear that, since it appears to be in a shop, that they would agree with that.
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Just keep a eye on it for any hint of crack formation. Until you see a crack you're reasonably OK. At the first hint of a crack, you're well past the beginning of the end.
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Other than the dent, is the downtube generally straight?
The Downtube is generally under tension, except in certain bump/crash situations. Thus, it shouldn't collapse more unless you rear-end a car, or hit a very deep pothole/road crack.
The Slingshot.
It is hard to tell exactly where your damage is, but I'm guessing maybe 1/3 along the distance of the downtube, closest to the bottom bracket. That should be a fairly low stress area, away from both the bottom bracket and the headtube.
If it was otherwise straight, I'd probably ride it. But, also inspect it regularly for progression. One problem is that it appears as if the paint is cracked, but probably not the underlying aluminum. I wouldn't fill it (which could mask a problem), but might consider stripping and repainting in the general vicinity of the damage, just so one could notice potential cracks forming in the metal easier.
The Downtube is generally under tension, except in certain bump/crash situations. Thus, it shouldn't collapse more unless you rear-end a car, or hit a very deep pothole/road crack.
The Slingshot.
It is hard to tell exactly where your damage is, but I'm guessing maybe 1/3 along the distance of the downtube, closest to the bottom bracket. That should be a fairly low stress area, away from both the bottom bracket and the headtube.
If it was otherwise straight, I'd probably ride it. But, also inspect it regularly for progression. One problem is that it appears as if the paint is cracked, but probably not the underlying aluminum. I wouldn't fill it (which could mask a problem), but might consider stripping and repainting in the general vicinity of the damage, just so one could notice potential cracks forming in the metal easier.
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Other than the dent, is the downtube generally straight?
The Downtube is generally under tension, except in certain bump/crash situations. Thus, it shouldn't collapse more unless you rear-end a car, or hit a very deep pothole/road crack.
It is hard to tell exactly where your damage is, but I'm guessing maybe 1/3 along the distance of the downtube, closest to the bottom bracket. That should be a fairly low stress area, away from both the bottom bracket and the headtube.
If it was otherwise straight, I'd probably ride it. But, also inspect it regularly for progression. One problem is that it appears as if the paint is cracked, but probably not the underlying aluminum. I wouldn't fill it (which could mask a problem), but might consider stripping and repainting in the general vicinity of the damage, just so one could notice potential cracks forming in the metal easier.
The Downtube is generally under tension, except in certain bump/crash situations. Thus, it shouldn't collapse more unless you rear-end a car, or hit a very deep pothole/road crack.
It is hard to tell exactly where your damage is, but I'm guessing maybe 1/3 along the distance of the downtube, closest to the bottom bracket. That should be a fairly low stress area, away from both the bottom bracket and the headtube.
If it was otherwise straight, I'd probably ride it. But, also inspect it regularly for progression. One problem is that it appears as if the paint is cracked, but probably not the underlying aluminum. I wouldn't fill it (which could mask a problem), but might consider stripping and repainting in the general vicinity of the damage, just so one could notice potential cracks forming in the metal easier.
It's actually a hybrid that I picked up for cheap for when friends of the right height want to tool around town. So won't be used much.
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Stand an empty beer bottle on your kitchen counter, then carefully balance another upside down so they're neck to neck. These are to (very crudely) simulate a tube that's cracked all the way around. Now press then upper bottle straight down and note that despite being two parts, the "tube" can take a decent load.
Now carefully pick the pair up holding both and keeping them together upright. OK so far? Now let go of the bottom one.
The point is that if you're worried about a structural member cracking and breaking, worry about tension members which simply pull apart, not compression members that will still stay put because they have no place to go.
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FB
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An ounce of diagnosis is worth a pound of cure.
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WARNING, I'm from New York. Thin skinned people should maintain safe distance.
Last edited by FBinNY; 02-03-18 at 10:49 PM.
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The hybrids should be somewhat sturdier than road bikes which is a plus. But, there are also thousands of cheap hybrid frames and junk bikes out there, although perhaps not as pretty as that one.
I'm a little more risk adverse when loaning stuff out. At the same time, it is often better not to loan out one's best either.
Assuming you loan it out for no more than a week or two at a time, expecting maybe a couple hundred miles tops, you can make it a general rule to inspect before and after it is loaned out.
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With respect to Cliff, let me propose something of a thought experiment.
Stand an empty beer bottle on your kitchen counter, then carefully balance another upside down so they're neck to neck. These are to (very crudely) simulate a tube that's cracked all the way around. Now press then upper bottle straight down and note that despite being two parts, the "tube" can take a decent load.
Now carefully pick the pair up holding both and keeping them together upright. OK so far? Now let go of the bottom one.
The point is that if you're worried about a structural member cracking and breaking, worry about tension members which simply pull apart, not compression members that will still stay put because they have no place to go.
Stand an empty beer bottle on your kitchen counter, then carefully balance another upside down so they're neck to neck. These are to (very crudely) simulate a tube that's cracked all the way around. Now press then upper bottle straight down and note that despite being two parts, the "tube" can take a decent load.
Now carefully pick the pair up holding both and keeping them together upright. OK so far? Now let go of the bottom one.
The point is that if you're worried about a structural member cracking and breaking, worry about tension members which simply pull apart, not compression members that will still stay put because they have no place to go.
But another thought experiment.
Take an empty soda can.
Stack... hmmm, say a 20 pound steel weight on it. And it may well take the weight if generally balanced.
Now crumple the side of that can (without getting your fingers under the weight), and put your 20 pound weight back on it.
Can you figure out how to attach as string to your crumpled can and see if it can lift that 20 pound weight without disintegrating?
I suppose one thing. Pay attention if your bike is "talking to you". Which, of course, is easier if you're riding your own bike rather than loaning it out.
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Hmmm... yes, if you have a crack or a break.
But another thought experiment.
Take an empty soda can.
Stack... hmmm, say a 20 pound steel weight on it. And it may well take the weight if generally balanced.
Now crumple the side of that can (without getting your fingers under the weight), and put your 20 pound weight back on it.
Can you figure out how to attach as string to your crumpled can and see if it can lift that 20 pound weight without disintegrating?
But another thought experiment.
Take an empty soda can.
Stack... hmmm, say a 20 pound steel weight on it. And it may well take the weight if generally balanced.
Now crumple the side of that can (without getting your fingers under the weight), and put your 20 pound weight back on it.
Can you figure out how to attach as string to your crumpled can and see if it can lift that 20 pound weight without disintegrating?
But put both ideas into the context of the modalities of failure that actually happen on bikes. I doubt you'll find a single example of compression buckling of a tube, vs plenty of tension failures leading to crashes.
Frame tubes are greatly overbuilt for pure compression or tension loads because they have to take bending loads which are far more demanding. But when they fatigue and crack, they act like those two beer bottles and it's tension failures that lead to crashes.
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WARNING, I'm from New York. Thin skinned people should maintain safe distance.
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Yes, the lateral flexing creates the stresses that ultimately will cause fatigue and cracking. My post wasn't about what would lead to fatigue and cracks as much as the consequences when it happens.
As one thinks about failure, think about what will happen, and whether the outcome is more likely to lead to inconvenience or injury.
As one thinks about failure, think about what will happen, and whether the outcome is more likely to lead to inconvenience or injury.
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FB
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An ounce of diagnosis is worth a pound of cure.
Just because I'm tired of arguing, doesn't mean you're right.
“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN
WARNING, I'm from New York. Thin skinned people should maintain safe distance.
#12
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it would make a great permanent trainer or roller bike.
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When that dent goes, it will feel soft briefly and then break. I would not trust it.
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But another thought experiment.
Take an empty soda can.
Stack... hmmm, say a 20 pound steel weight on it. And it may well take the weight if generally balanced.
Now crumple the side of that can (without getting your fingers under the weight), and put your 20 pound weight back on it.
Take an empty soda can.
Stack... hmmm, say a 20 pound steel weight on it. And it may well take the weight if generally balanced.
Now crumple the side of that can (without getting your fingers under the weight), and put your 20 pound weight back on it.
No relation to the OP's bike; I would have no reservations about riding that frame. A little dimple in a tube that's mostly under tension isn't likely to cause trouble.
Steve
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+1. Also I would guess that being a hybrid, Specialized probably used some thicker, sturdy tubing that will hold up to the dent better than some lightweight road frames.
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Wrapping could hide potential problems, although a good fiberglass (or carbon fiber) job should add strength to the area if applied well, and thus should be a positive.
Tape, decals, or body filler on the other hand could potentially hide the formation of cracks.
Could you fill the tube with long fiber reinforced resin?
Tape, decals, or body filler on the other hand could potentially hide the formation of cracks.
Could you fill the tube with long fiber reinforced resin?
#20
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Myself, hybrids are a dime a dozen. I would pick up a replacement hybrid frame and do a parts swap. A bike with that kind of damage can typically be purchased at a low price anyway, so the economics after the swap should still be OK. I would then donate the fork to a co-op (and hopefully find a hybrid frame at a co-op too).
I wouldn't call that damage slight. At the same time, I don't see it suddenly ass-ploding either.
I wouldn't call that damage slight. At the same time, I don't see it suddenly ass-ploding either.
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Still, one could clean up a $20 frame. Give it a clean paint job. Throw on the Sirrus fork, and build it up and it might come out pretty nice.
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If it were my bike, I'd still ride it and just watch it more closely for signs of impending failure.
Might be a little cautious about letting others ride it just because of the additional legal liability. Though I can't remember when someone else ever rode my bike. Probably not since junior high 50 some years ago.
I'd never buy one that's dented that badly.
Might be a little cautious about letting others ride it just because of the additional legal liability. Though I can't remember when someone else ever rode my bike. Probably not since junior high 50 some years ago.
I'd never buy one that's dented that badly.
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Dont strip the paint as any anodized areas removed takes away the treated aluminum coating. If anything, leave it be.
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#24
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TallRider, No doubt the frame's longevity is compromised. My experience with aluminum frames has been that those with a sharply creased dent are more likely to fail than a rounded dent, which may never fail in our lifetime.
Regardless of frame material damaged, it is the owner's judgement call. Anyone the bike is lent to should be aware of the damage.
Brad
Regardless of frame material damaged, it is the owner's judgement call. Anyone the bike is lent to should be aware of the damage.
Brad
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The experiment I recall from high school was to put a small (3"x3") piece of wood or a book on top of a beer can. Stand on said book, balancing yourself (and at the same time the forces) on the beer can. I weighed 220, and could easily do this, balancing on one leg. Then bend over while you are still on the beer can, and gently tap opposite sides of the beer can, drawing your fingers away as quickly as possible. The can collapses in a heartbeat.
In a normal bike, your peddling action will induce bending moment on that down-tube. Given that I still weigh over 200 (more than 220!) and I get up to over 40mph, I would not trust that frame. That's just me, though.
In a normal bike, your peddling action will induce bending moment on that down-tube. Given that I still weigh over 200 (more than 220!) and I get up to over 40mph, I would not trust that frame. That's just me, though.