Triple butting?

[Climb01742]

would someone be kind enough to explain triple butting to me, what it is and why it is (or isn't?) a good thing. is there single- and double-butting? and with all this butting going on, how does it impact a frame's ride? many thanks. triple-thanks, even.

[Ozz]

"butting" a tube or spoke is basically just a way to put more material where it is needed (high stress or welded/brazed areas) and less material where it is not needed (low stress or unwelded/brazed areas). This gives you lighter weight, better performing spokes and tubes.

Double butting means you essentially have two thicknesses of material throughout the length of the tube or spoke. With tubes, you are concerned about thickness of the tube wall, with spokes you are concerned about the diameter of the spoke.

For example, a double butted spoke is 2.0mm at each end, and 1.8mm in the middle.

Triple butting means you are referring to three thicknesses or diameters.

For example, a triple butted spoke is 2.3mm at the hub end, 1.8mm in the middle, and 2.0mm at the rim end.

Butting is a good thing because it lets you "tune' the material to suit your needs. In the case of spokes, butted spokes are stronger because the middle is "weaker' than the ends. Since most of the stress on spokes is at the ends, having a weaker middle transfers loads / the flexing to the middle of the spoke where it is less likely to fail. Therefore, you have better spoke durability. Most spokes fail at the elbow...

In the case of tubes, I imagine the same principles apply.

FWIW - Sorry for the emphasis on spokes, I have been spending too much time reading Jobst Brandt's book.....

[JohnS]

I thought I read (in the Serotta catalog?) that butting of tubes doesn't affect the ride. It's strictly for weight purposes.

[Ozz]

I suppose it affects the ride in as much as a light bike rides differently than a heavy bike....

Beyond that, I agree that the type of material, shape (Colorado Concept) of the tubes, and especially the knowledge of the builder (fit & geometry) have more to do with how the frame rides than does the butting of the tubes.

I am happy to be corrected on this point...

[bags27]

My understanding is the same as JohnS's. This question came up in the previous version of the Phorum, and Tom Kellogg agreed there that the butting affects weight, but not strength or ride. I've since ordered a Ti bike from Tom and when it came time to decide on the butting, he told me that double butting would save about 10 ounzes (for an approximately 58 virtual TT) at an additional cost of $300. Seemed worth it to me (of course, the day you're buying you lose all fiscal sanity).

[bubba]

Originally posted by bags27
My understanding is the same as JohnS's. This question came up in the previous version of the Phorum, and Tom Kellogg agreed there that the butting affects weight, but not strength or ride. Well,a tube that is thinner in the middle,will have less strength,everything else being equal.

[JohnS]

It just has to be strong enough, which a butted tube is.

[Chief]

Structures, including bicycle frames, like to resist loads through direct action (in tension or compression), but joints, welds, or any change in geometry of a structure produce local flexing that introduces stress concentrations. These stress concentrations can be minimized by adding additional material to these regions and that is precisely what "butting" does. Butting tends to produce a more uniform stress distribution throughout the length of a tube and, therefore, uniform strength so that the strength at the joint is the same as that at the center of the tube even though the tube may be thinnner at its center. Triple butting is an attempt to produce an even more uniform stress (strength) distribution than can be achieved with double butting. Ideally one would like to have a continous change in the wall thickness to produce a truly unifrom strength, but since this is not cost effective, double or triple is used and suffices. When necessary, butting can also be used to stiffen a joint or region. Through butting one can achieve the an optium design; i.e., a design for which its weight is a minimum for a specified strength or stiffness.

[Climb01742]

with ti tubes, i suppose the difference in strength would be between incredibly strong and mind-bendingly strong.