Strength of bottom bracket housing with nothing inside?
#1
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Strength of bottom bracket housing with nothing inside?
I realize it might be difficult to figure and it varies from bike to bike, but generally speaking...
What would you guess is the strength of a bottom bracket housing tube? I mean, just the round steel tube with nothing inside of it. The tube that the three (or four) parts are welded to. The part that a bottom bracket screws into. Less generally... I'm talking about a larger tube that requires an adapter to screw a modular bottom bracket into. I suspect the larger diameter bottom bracket housing would be less strong. But I'm only asking for guesses about anything.
If you use the bottom bracket area with nothing inside of it, does that weaken it to the point of breaking? I'm guessing the innards provide some strength, but maybe not so much that it makes a big difference.
I'm asking for guesses since the subject might never have even come up before.
Thanks.
What would you guess is the strength of a bottom bracket housing tube? I mean, just the round steel tube with nothing inside of it. The tube that the three (or four) parts are welded to. The part that a bottom bracket screws into. Less generally... I'm talking about a larger tube that requires an adapter to screw a modular bottom bracket into. I suspect the larger diameter bottom bracket housing would be less strong. But I'm only asking for guesses about anything.
If you use the bottom bracket area with nothing inside of it, does that weaken it to the point of breaking? I'm guessing the innards provide some strength, but maybe not so much that it makes a big difference.
I'm asking for guesses since the subject might never have even come up before.
Thanks.
#2
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Although I doubt there is any chance that the bb housing itself will fail, I would guess larger diameter tubes in general are stronger.
John
John
Last edited by 70sSanO; 10-12-20 at 10:29 AM.
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#3
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Strong enough to tolerate what?
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They're usually very strong although they're available in different sizes. They're all 34.8mm on the inside (English threads) and some are as much as 40mm on the outside. That's 2.6mm wall thickness. And they're usually cromoly as well (rather unnecessarily given how thick they are). The other tubes on the bike are usually about 0.5mm increasing to 0.8mm at the ends to give you an idea how thick that is.
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How could you test this? Without the spindle, bearings, cups and crankarms installed you can't ride the bike except to push it along with your feet on the ground. I expect that wouldn't put much strain on the bottom bracket
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That said, I'd buy a cheap bottom bracket and install that if I was worried about transporting a crank-/BB-less frame.
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It's not too hard to find the mechanical properties of 4130 steel. ASM Material Data Sheet
The real question is what kind of strength are you looking for? resistance to crushing? shear strength?
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It is strong enough for its intended use and that includes holding the BB assembly. Its equivalent to asking the question of "how strong is an innertube."
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This sounds like someone wanting to use a bike frame for something with a motor in it.
Which would probably not be a great idea.
Which would probably not be a great idea.
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Not sure if you are trolling or simply clueless but a BB with nothing inside of it should last forever, never wear out and never break, because after all it won't be used for anything.
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It's not too hard to find the mechanical properties of 4130 steel. ASM Material Data Sheet
The real question is what kind of strength are you looking for? resistance to crushing? shear strength?
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You're thinking of 1030 steel or the equivalent. 4130 is chromium-molybdenum, e.g., Columbus SL tubing.
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I build steel bike frames. I can assure you that almost all of the bottom brackets in quality welded steel bike frames are made from 4130 tube. Dept. store bikes are made from mild steel or Hi-tensile steel.
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