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Thread: Thinwall tubing

  1. #1
    Senior Member Road Fan's Avatar
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    Thinwall tubing

    Looking at a frame made with thinwall tubing in standard non-oversized diameters. TT 7/4/7, DT 8/5/8, ST 9/6. The OD's would be respectively 25.4, 28.6, 28.6. The builders say the steel will be non-heat-treated. I assume the alloy is at least 4130. My question is, is it acceptable to have such thin tubing walls without a heat-treated, higher strength alloy such as Nivachrome or 853? Seems to me the main risk here is ease of denting the tubes - higher yield strength should absorb more force or impact without yielding.

    What do you say?

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    Randomhead
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    be careful with it any you should be fine

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    Nobody mconlonx's Avatar
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    Quote Originally Posted by Road Fan View Post
    Looking at a frame made with thinwall tubing in standard non-oversized diameters. TT 7/4/7, DT 8/5/8, ST 9/6. The OD's would be respectively 25.4, 28.6, 28.6. The builders say the steel will be non-heat-treated. I assume the alloy is at least 4130. My question is, is it acceptable to have such thin tubing walls without a heat-treated, higher strength alloy such as Nivachrome or 853? Seems to me the main risk here is ease of denting the tubes - higher yield strength should absorb more force or impact without yielding.

    What do you say?
    I assume you've already voiced this concern to your builder...?
    I know next to nothing. I am frequently wrong.

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    Senior Member Road Fan's Avatar
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    Actually a small manufacturer rather than a custom builder, so there isn't full flexibility. I have expressed the concern, yes. I'm expecting a response next week.

    I use a car-trunk rack to transport bikes when I'm taking more than two. Since it clamps on the TT of the bike, I think I should get a stronger steel if I can. I haven't signed up for this bike yet, but it is a good geo, and I like the standard diameters.

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    If you can't get the answers you seek, either from the tube maker, or the bike builder, I'd look elsewhere. 7/4/7 is some pretty lightweight (thinwall) stuff. I'm not aware of any manufacturers producing these tubes who don't specify how it should be used, whether it needs post weld heat treat etc. Then you have butt lengths- different for lugged vs. fillet. Really, if the outfit you're considering to build the frame can't answer the questions, look elsewhere.

    You like the geo?, and the tube sizes? Any custom builder can provide what you prefer- but he may have suggestions to the contrary based on his opinions to your personal needs.

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    Senior Member Road Fan's Avatar
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    The bike builder's lead guy has said he'll look at upgrading the alloy across his range for this frame design. Again, it isn't a custom build. If he's willing, I'm down. If not, I go elsewhere as you say.

    Regarding the tubing maker, the frames are to be built in small batches in Asia. The builder (really the bike builder) doesn't disclose all his supply chain details, for better or worse, and it may be that his frame supplier keeps his cards close to his belt as well. There isn't the openness you expect from a bespoke builder, and there won't be.

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    Nobody mconlonx's Avatar
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    Meh. Most trunk racks are glorified rubber bands or ski-buckles holding your bike to the rack--wouldn't think tubing diameter would be an issue. If it's some kind of work stand like clamping system, there might be issues.

    That said, I'd not be carrying anything I really cared about and/or spent real money on, with a trunk rack...
    I know next to nothing. I am frequently wrong.

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    Senior Member Road Fan's Avatar
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    Why not?

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    Well the old "beer can rule" said that the safe maximal ratio of diameter to wall thickness was 50 to 1 for ordinary alloy steel, rising with yield strength for heat treated steels*. The rule is entirely empirical but is based on the theory of shell buckling.

    Your ratios are 25.4 / 0.4 = 63.5 , 28.6 / 0.5 = 57.2 and 28.6 / 0.6 = 47.7. By the old rule you'll need heat treated steel for the first two.

    *I think I can remember old Eric Hendren saying that the ratio was roughly equal to the yield strength in tons per square inch, but I may be confabulating here. I last spoke to Eric over 30 years ago.

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    Nobody mconlonx's Avatar
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    Quote Originally Posted by Road Fan View Post
    Why not?
    Messing up a paint job, theft, exposure to elements during transport (New England salt...)...
    I know next to nothing. I am frequently wrong.

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    Senior Member GrayJay's Avatar
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    Quote Originally Posted by Road Fan View Post
    Looking at a frame made with thinwall tubing in standard non-oversized diameters. TT 7/4/7, DT 8/5/8, ST 9/6. The OD's would be respectively 25.4, 28.6, 28.6.
    Standard diameters and thinwalls, sounds like a recipie for making a noodle of a frame.

  12. #12
    Senior Member Road Fan's Avatar
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    The point is for a randonneuse, not a city criterium racer. But compare to 531 Competition: 8/5/8 TT and 9/6/9 DT, and to 753: 7/5/7 and 8/5/8 TT and DT. It's lighter, but not by a whole lot.
    Last edited by Road Fan; 01-10-12 at 06:14 PM.

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    Randomhead
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    when I read your first post I thought that it sounded like 531 SL (or C) which was well-hated. Aren't you fairly tall? 753 was heat treated, so it's not really a good comparison

  14. #14
    Senior Member Road Fan's Avatar
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    Me? no, I'm 5'6", I ride frames 53 cm through 56, though that is usually a stretch.

    The frame in question will have tubing of unstated origin. If it was actually Reynolds it would have been bragged about, considering the low price point. This company has a kind of "plain brown wrapper" feel. The manufacturer will say the guage and OD, but so far not the alloy, heat treating, or sourcing.

    Correct me if I'm wrong, but heat treating does not change the modulus of elasticity (i.e. stiffness) of an alloy or a tube. It increases the yield strength, but not the modulus of elasticity. My reason for wanting heat treating is to reduce the likelihood of denting - improve reliability and durability. I don't expect it to improve the ride quality or liveliness.

    In any case, I mentioned 531 (Competition, not the super-light stuff) and 753 (same guage as the super-light, lighter than the Competition, and still heavier than what my manufacturer is planning) to illustrate the lightness of the tubing he is planning to use.

    I'm not too concerned about the thin walls - I think one man's noodly is another man's responsive.
    Last edited by Road Fan; 01-10-12 at 07:30 PM.

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    Well, 9/6/9 isn't really considered thin wall. I guess I'd call that "standard thickness" tubing in traditional diameters. It'll dent, of course, but is probably more damage resistant than most of the tubing used in modern bicycles today.

    Non heat treated 8/5/8 tubing is/was pretty common for general use. I've never heard of any issues with denting, etc. I've even used it in some of my own frames, despite leaning toward the Clydesdale end of the spectrum, and have had no troubles, other than more flex than I really prefer.

    7/4/7 is too thin for me and was even when I was racing at 168 pounds, on a 58 cm. frame, so my experience is more limited. When I was coaching track racers a couple of decades ago, several of "my" riders used 7/4/7 frames without problem. My wife, whom I stole from a collegiate racing team when they forgot to pay me, has had a 7/4/7 pursuit frame for 15 years or so and really likes it - and it's still pristine despite extensive travel and four or five moves.

    So, FWIW, I think the tubing selection you mention would be ideal for a bike for your weight, in your size, and for your purpose, and I don't think you need to be especially concerned with denting it. Worst "real" case scenario is a top tube dent from crashing, which is primarily cosmetic and could be fixed by filling with silver brazing material - although that would require a repaint, of course.

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    Also, re. "planing" vs. "noodly", I personally find that bottom bracket flex doesn't bother me, but top tube flex does. IOW, I don't notice BB flex, but TT flex can result in a bike that handles weird and is always calling attention to itself. In a 54 or 55 cm. frame with an appropriate length top tube, my opinion is that with your tubing selection you will get the "planing" Jan talks about, without the whippy feeling on the front end that can be so annoying.

    Oh, and you are right about heat treatment - it makes the tube more resistant to denting (and also allows it to put up with more cycles before failure) but doesn't affect flexibility to any significant degree.

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    Quote Originally Posted by Road Fan View Post
    Looking at a frame made with thinwall tubing in standard non-oversized diameters. TT 7/4/7, DT 8/5/8, ST 9/6. The OD's would be respectively 25.4, 28.6, 28.6. The builders say the steel will be non-heat-treated. I assume the alloy is at least 4130. My question is, is it acceptable to have such thin tubing walls without a heat-treated, higher strength alloy such as Nivachrome or 853? Seems to me the main risk here is ease of denting the tubes - higher yield strength should absorb more force or impact without yielding.

    What do you say?
    Why would the ST be thicker-walled than the DT? That sounds backwards, and would give you a less-than-27.2 post size. Usually, a ST is .5/.8 and a DT is .9/.6/.9 (that's what standard 531DB was for decades, for example).
    If you have those two reversed, then those aren't particularly thin. Just the TT is 0.1 mm thicker than 'standard.' No big deal at all. Top tubes don't do much, really. Is it Kaisei tubing?

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    What matters imo is primarily the 'keel' of the bike - fork blades, down tube, chainstays. Other stuff can be pretty thin-walled without losing much stiffness.

    Since the builder won't tell you where the tubing is coming from, I would assume Taiwan. Is it at least seamless tubing? Not that seamed is bad per se, but we're talking Taiwanese (?) tubing of undisclosed origin/alloy, so if it is least seamless, I'd consider that a plus.

  19. #19
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by 753proguy View Post
    Why would the ST be thicker-walled than the DT? That sounds backwards, and would give you a less-than-27.2 post size. Usually, a ST is .5/.8 and a DT is .9/.6/.9 (that's what standard 531DB was for decades, for example).
    If you have those two reversed, then those aren't particularly thin. Just the TT is 0.1 mm thicker than 'standard.' No big deal at all. Top tubes don't do much, really. Is it Kaisei tubing?
    In this case it is Taiwan because that's where the frames will be made, and I don't know if it's seamless. It's not that he refused to tell, but that nobody seems to have asked him. As far as the conventional wall thickness criteria, I tend to agree with you, but this is what he said he's doing. Just based on price, it's not Kaisei. I'm well aware of the conventions set by 531, but the convention set by Columbus SL is for 9/6/9 in all three tubes. And some makers, notably Trek, deviated from the 531 standard. DT was 10/7/10 rather than 9/6/9 at least in the 1981 through 1984 531C and 531CS, if one may believe their brochures on Vintage-Trek, and I see no reason not to.

    And (I think I said) I've ridden bikes with both the Trek 531 (my 1984 610 with original fork and a special Dediaccaia high-rake 60+ mm fork), and my former Woodrup with (as marked) standard 531 tubing and the early fork blades (Imperial?). The 610, even with the high-rake fork, is still stiffer than the Woodrup, in terms of bump tracking. So I'd say your keel design info is accurate, but for this bike I'm looking for more flex. See the posting above by Six Jours, who's built a few LD bikes, regarding flex v. noodling.

    But really my original point in starting this discussion was to gain input on whether the chosen wall thicknesses should be implemented in a heat-treated steel or a standard 4130. My question was not based on ride quality, since flex properties are not affected by heat-treating and should not be expected to change. What may be expected to change are durability and crash survivability of the frame.

    That's actually not a question anymore, since the builder has announced in his blog that he's changing the design spec to a heat-treated steel.

    If you'd like to dialog with the frame company about their design, pm me and I'll give you their info. No need to drag them through anything here - my question is more about appropriate frame engineering than anything else.
    Last edited by Road Fan; 02-05-12 at 10:17 AM.

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    Andrew R Stewart Andrew R Stewart's Avatar
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    Don't think i'd use such thin wall a TT on that kind of bike. It seems to me that stability on unknown surfaces, down hills with less shimmy potential (espically with any extra weight on the rack or bars) and less concerns about transporting the bike would rank as higher needs then the once or or of saved weight.

    Why people with nice paint jobs or carbon frames use behind the car racks that hang the bike by the Tt escapes me some times. Andy.

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    coprolite fietsbob's Avatar
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    Rider better not be a Clydesdale..

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    Quote Originally Posted by Road Fan View Post
    In this case it is Taiwan because that's where the frames will be made, and I don't know if it's seamless. It's not that he refused to tell, but that nobody seems to have asked him. As far as the conventional wall thickness criteria, I tend to agree with you, but this is what he said he's doing. Just based on price, it's not Kaisei. I'm well aware of the conventions set by 531, but the convention set by Columbus SL is for 9/6/9 in all three tubes. And some makers, notably Trek, deviated from the 531 standard. DT was 10/7/10 rather than 9/6/9 at least in the 1981 through 1984 531C and 531CS, if one may believe their brochures on Vintage-Trek, and I see no reason not to.

    And (I think I said) I've ridden bikes with both the Trek 531 (my 1984 610 with original fork and a special Dediaccaia high-rake 60+ mm fork), and my former Woodrup with (as marked) standard 531 tubing and the early fork blades (Imperial?). The 610, even with the high-rake fork, is still stiffer than the Woodrup, in terms of bump tracking. So I'd say your keel design info is accurate, but for this bike I'm looking for more flex. See the posting above by Six Jours, who's built a few LD bikes, regarding flex v. noodling.

    But really my original point in starting this discussion was to gain input on whether the chosen wall thicknesses should be implemented in a heat-treated steel or a standard 4130. My question was not based on ride quality, since flex properties are not affected by heat-treating and should not be expected to change. What may be expected to change are durability and crash survivability of the frame.

    That's actually not a question anymore, since the builder has announced in his blog that he's changing the design spec to a heat-treated steel.

    If you'd like to dialog with the frame company about their design, pm me and I'll give you their info. No need to drag them through anything here - my question is more about appropriate frame engineering than anything else.
    Not sure what exactly your point is here, but I guess the bottom line is that you get what you pay for. I'll stand by what I said, which was primarily the following: that is an odd combination of tubing gauges being proposed, in my opinion, and I would reverse the ST/DT gauges, but overall it's not going to be that big of a deal for a 53-ish traditional frame for a person of your size and weight.

  23. #23
    Senior Member Road Fan's Avatar
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    You've actually raised a new point in the thread. My original concern in starting the thread has been satisfied. Have fun with yours.

    I thought I said pretty clearly, if you want to speak to the designer about it, I can put you in touch with him. There's nothing to be gained by convincing me. I am not the designer.

    So, fine, stand by what you say. I am not arguing with you.

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