Test for butted tubes?
 

I always read about double butted tubes on bicycle frames. Is there a way to know if a frame has butted tubes if the original sticker is missing? An X-ray scan seems a little expensive.

Flick with your fingernail from end to the middle and you should hear the change of sound.

You could also weigh it. A butted tubing frame should be considerably lighter than a straight gauge tubing frame. I am sure someone on this forum or the interwebz knows what either butted or straight should weigh give or take a few ounces for a given size.

If the frame weighs four or five pounds then you're good. Just for example my Paragon (56cm, Ishiwata 024, fairly stout) weighs 5.5 lb with headset cups and a BB installed.

Some mid-grade frames are made only partly of butted tubes, or they are made of straight chromoly that's still thinner than hi-ten. There's a spectrum!

Actually, there's no reliable way to be sure. Weight may work to separate a good quality frame from one of much lower quality, but things get close near the upper end, and variables like lugs, BB shell or whatever make it hard to distinguish between butted and high quality plain gauge tubing. Also, know that both butted and plain gauge tubes come in various wall thicknesses, further muddying that water.

There are other indicators, that may help, possibly the most significant of which is the seat post size which will tell you the wall thickness of the seat tube.

Otherwise, the best indicator is to know the maker, and what the specs call for.

So, for example, show me what appears to be a high end British or US made steel frame, which takes a 27.2mm seatpost, and I'll very willingly bet a few beers that it's Reynolds 531 or better tubing. Likewise you might see a mark on the steerer if you remove the fork.

BTW - many (most) makers of top end steel tube sets, mark the tubes themselves. One place to find such a mark is at the bottom of the seat tube, a few inches above the bottom bracket. Besides identifying the tubing, the marks also tell builders which end to cut (or not) when cutting tube to size.

Sound, if your ear is trained. I'd try it without anything in the frame. No wheels, seatpost, BB, etc if I was really concerned.

If you want to know for certain then cut a tube in a few spots and measure. ;)

Seriously, if it were me and the frame fit I'd just ride it and not worry either way.

That's what I think too.

I think that we have a tendency to think that if we can identify all of the individual strokes we could create the Mona Lisa.

This. You will definitely hear a difference.

I'll have to try flicking some tubes to test that method/theory. I'm a percussionist, and just knowing the nature of how things sound when you hit them, I wouldn't have expected butting to make much of a difference if the butt is near the end of the tube where it's welded or fitted into a lug.

I'm a musician and luthier too. I did the tap test on the bare frame and the pitch didn't change when I hit the tubes near the lugs or the center. What changed was, obviously, the sustain.

It's a cheap '70s bike so I don't think it's made with butted tubes, but I just thought it might be nice to try the test anyway.

I own single, double, and even triple butted steel bikes. One thing I've noticed when doing the finger nail tap test is that when you get close to the joint the sound changes no matter how many "butts" :lol: you have. I'm not sure how anyone can figure it out based on the sound, but then again I'm not a musician.

Isn't marketing wonderful?

Where do you think they put that 3rd butt? Or does that mean that you're the butt of a marketing inside joke?

However, I agree that the so-called ring test is meaningless, especially without a reference sample to compare to, unless one has perfect pitch. But I don't make a point of trying to prove that.




BTW- I already know what marketers mean when they say triple butted, so no explanation is needed here.

I assumed the "3rd butt" is near the center of the length of the tube... as in the tube actually has three different wall thicknesses, but maybe you know something I don't?

Maybe I do, but let's not go there.

A single butted tube, such as is used for the seat tube has one reinforced (buttressed) end.
a double butted tube, used for the top and down tubes, is thicker at both ends (and thinner in the middle).

I believe* that a triple butted tube is analogous to a triple butted spoke, where the two ends are of different thickness. So you have 3 gauges, the thicker end, the not as thick end, and the middle which is thinnest.

But no matter what marketing calls it, you can only buttress 2 ends of a tube. (except in 4 dimensional space, where tubes might have 3 ends)


* I said believe, because while I've described one use of the term I'm familiar with, I have no way of knowing what marketing is up to these days.

I'll take a crack at that, though. A tube, by itself, will not change in pitch (it's fundamental), regardless of where you hit it... Think a chime. What the butting *does* add is overtones--which are, more or less, completely indistinguishable, since an assembled frame has more in common with an un-tuned bell (several tubes of varying thicknesses/lengths/butting, resulting in a mishmash of tones), than a musical instrument.

All of that assumes a frame that is tapped/rapped while hanging from a cord, with nothing built on it. All the "tap test" proves is that the ends of the individual tubes are, indeed, fixed into another part of the bike, and less prone to vibrate as a result.

As mentioned before in the thread, a maker's mark and other key clues (seat tube ID, weight, model) are better indicators of what the bike may be made of without destructive testing.

Not pointed at you, just general information for the (hopeful) edification of the masses.

The thinner material in a butted tube does sound different when given the finger nail tap. If you don't hear a difference, your tube isn't butted.

A tried and true test shown to me by a bike mechanic back in the early 70s.

A tube can have multiple wall thicknesses in it, making it multiple butted. Were they better than double butted? I have a quad butted Fuji, I'm sure it's a bit lighter than an identical size frame made with identical tubing that was double butted instead, but I doubt it's better.

Pose this question in CnV and see what answers you get.

An industrial xray machine would let you know for sure. There are many companies that offer xray inspection services. They could tell you if your frame was made from double butted tubes. Unfortunately that would be an expensive way to satisfy your curiosity.

What "marketing is up to these days" is not thinking about butted tubes, just as they haven't been for the past 15 or so years. In the rare instance where they do have copy to create for a triple butted tubeset, I can't see how they would reinvent the meaning, or to what end; it's not rocket science:

https://cdn.shopify.com/s/files/1/06...tted1.jpg?3417

IIRC, "triple-butting" only involved the down tube, and made a slightly thicker wall in the region where shift lever bosses would be attached.