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Thread: Cromoly parts.

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    Cromoly parts.

    Just how tough are cromoly parts? Has anyone had or seen a cromoly frame break? I'm curious because I've heard somewhere that cromoly frames break easily, but I don't know if that is true. Any opinions are welcome.

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    I couldn't car less. jeff williams's Avatar
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    Where did you hear that?
    Aluminium has a greater possibility of failure.
    Hi-Ten steel is not chromoly, not all chromoly is the same.
    4130 is considered a good chromoly steel.

    I have a 12 yr old Ritchey chromoly stem on my mtb, I doubt it will EVER break.
    I was under the impression that most HQ bmx are 4130.

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    Senior Member BMXTRIX's Avatar
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    Steel comes in many flavors with 4130 being one of the most typical used in bicycle frame manufacturing.

    For freestyle specifically it holds properties that allow it to be very durable under very harsh conditions that other cycling sports don't put on bikes. Road, mountain, and bmx (racing) bikes are often aluminum or (sometimes) titanium as the stress that is put on these bikes, while significant, is typically predictable and from specific directions. That is, they can build up exactly where stress will occur to compensate.

    Street, dirt, vert, and to a lesser extent, flatland, all put an incredible amount of stress on almost every point of a bike and the stress levels constantly change which means a durable, but somewhat flexible frame material is needed. You don't want it to be to brittle or stiff like aluminum, or the shock must be entirely taken by the frame. So, 4130 has a certain amount of flex inherent to the steel that helps prevent fatigue in the metal. Titanium is an incredible metal, but it is actually to flexy and continued high pressures from different angles can warp the frame and bend it out of shape much more quickly than 4130.

    4130 itself is just one of many versions of chromoly. You may see bars made of 4140 or axles made of 4140 chromoly. You can also treat chromoly to make it stronger. Heat treating, stress releiving, air hardening... The list is fairly long and the physics behind how it works is pretty intense, but there are ways to keep the metal from becoming to brittle while still increasing strength.

    Anyway, I have seen 4130 frames break. 15 years ago a frame would last at most about 1-2 years for a rider who was serious at FLATLAND, and vert guys would go through a couple a year at least. Bars broke, frames snapped, seatposts failed, wheels sucked, etc., etc. Things are much stronger now, but the new found focus on bike weight over reliability is sure to spark a whole new generation of 14 year olds whining about how their 27 pound bike just isn't as strong as their friends 32 pound bike. Cripes, go on a diet, lose 5 pounds.

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    http://www2.sjsu.edu/orgs/asmtms/artcle/articl.htm This is a good article on the different materials used for building bike frames. Basically, aluminum is lighter than steel, but weaker. It is also stiffer. That's why they use bigger tubing (with mountainbikes anyway) when building Al frames- to compensate for the reduced strength (and of course they can keep weight down as well). I imagine most BMX bikes are steel since it has a bit of give to it compared to Al. I bet it'd be pretty painful to get air and then land on a rigid aluminum bike.

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    Quote Originally Posted by BMXTRIX
    Anyway, I have seen 4130 frames break. 15 years ago a frame would last at most about 1-2 years for a rider who was serious at FLATLAND, and vert guys would go through a couple a year at least. Bars broke, frames snapped, seatposts failed, wheels sucked, etc., etc. Things are much stronger now, but the new found focus on bike weight over reliability is sure to spark a whole new generation of 14 year olds whining about how their 27 pound bike just isn't as strong as their friends 32 pound bike. Cripes, go on a diet, lose 5 pounds.
    Your anwser is very detailed, I thank you for that. But the part of your post that I've highlighted almost sounds like an insult to me. I'm not over weight, in fact I'm slightly under weight, and I know lots of kids complain about their bikes being to light or heavy and not knowing what they want. But I'm not like that. All I was asking is how much stress a cromoly frame can take. If I'm mistaken on what you were implying on your post then I'm completely sorry. I don't talk on forums much so most of the time I don't get what people are implying when they anwser or talk to me. So again I'm utterly and completely sorry if I'm not understanding you or if I'm mistaken on what you were implying on your post, but it seemed awful close to an insult.

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    Senior Member BMXTRIX's Avatar
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    No offense was meant unless you are one of the ones who focuses on weight instead of having a quality bike. I do mean to offend anyone who is a weight wh0re, because... well, I don't want to hear from peope who are more concerned about the weight of their bike instead of having fun on their bike.

    Anyway, I could stand to lose AT LEAST 30 pounds. I'm a little over 180 now and about 150 would be much better for me to be at. I'm 5'8" so not that tall and way to short for my weight. On the other hand, I don't complain about the weight of my bike... The length, yes, the weight, no. I just save weight where I can and cut weight as I replace parts if it makes sense. Riding flatland though I love my short frame.

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    Quote Originally Posted by BMXTRIX
    No offense was meant unless you are one of the ones who focuses on weight instead of having a quality bike. I do mean to offend anyone who is a weight wh0re, because... well, I don't want to hear from peope who are more concerned about the weight of their bike instead of having fun on their bike.

    Anyway, I could stand to lose AT LEAST 30 pounds. I'm a little over 180 now and about 150 would be much better for me to be at. I'm 5'8" so not that tall and way to short for my weight. On the other hand, I don't complain about the weight of my bike... The length, yes, the weight, no. I just save weight where I can and cut weight as I replace parts if it makes sense. Riding flatland though I love my short frame.
    Ok thank you very very much BMXTRIX for clearing that up, and I'm very sorry for thinking that you'd insult me. No, I don't care about the weight of my bike, I just consider myself blessed that I can even have a bike as good as mine is! And I also don't worry about my weight either because I'm fifteen and I'm still growing (at least I hope I am! LOL) and I actually need to gain some weight! And you're right, BMX should be all about fun, not your bike specs, or your weight, or whatever any other obsessions maybe out there, so no one should ever lose sight of what BMX is really about. But anyway thanks man, you're a nice person and again I'm sorry for thinking that you were insulting me.

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    I had a craptacular gay Federal extension that hapen to be ******** and the headtube cracked off approx. 4 times. I tried to weld it but it such a piece it broke again. So now I took the liberty and did myself a favour and got a Kink Freebird frame.

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    You don't reweld headtubes. All that that is going to do is make it more prone to breaking again.

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    if you know how to weld and dont melt into the frame to much or too light it will be tough as steel

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    It is steel.

    The fact of the matter is that rewelding a joint isn't going to strengthen it at all, and it will be weaker than it was prior to breaking in the first place.

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    I hav'ent heard that

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    Rewelding of parts increases the brittleness of that area. Breaks tend to occur at welds not because the weld is weak, but because the metal right around the weld has been heated and cooled which makes it brittle. Stress relieving and heat treating can help reduce the brittleness of parts, especially around welds, which makes them stronger.

    You definitely CAN reweld any damn thing you want to, but you also are taking your life into your own hands when you do that as you are putting the metal through a second heat/cool process which is sure to make things much more brittle.

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    ive had a chromoly frame snap. it was three years old and had a happy life. i kinda miss it. it was a fit foster race.

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    Quote Originally Posted by Beerman
    You don't reweld headtubes. All that that is going to do is make it more prone to breaking again.
    I was prety sure it would break again soon, but I couldn't afford a new frame at that time. I got it welded for free so I could have as much time as possible on it, I just felt like riding.

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