I like Skol
A Minging Manc...
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- Sunny Ashton-under-Lyne
I understood "double butted" with regard to spokes as being the other way round to how the term is used with frames... ie the ends are narrower and the thicker bit is the middle section of the spoke, presumably for stiffness? Certainly this was the case on my RS30s which were described as double butted on the spoke, but someone in the know said they should be classed as "swaged" - except most buyers wouldn't know what that meant but would think "double butted" sounded swanky as so many frames go on about same.
Stu
A butted frame tube or a butted spoke are both the same, they get thicker at the ends because that is the point the stress forces have most effect and any failure is expected to happen. The rest of the tube/spoke can be thinner/lighter without compromising the overal strength of the structure. Double butted simply means both ends are butted. I can't think of many places on a bike frame where a tube would be single butted, perhaps the seat tube would be butted at the bottom where it is joined to the bottom bracket shell but not at the top?
A little off topic but this also leads on to 2 other reasons why frame tubes are butted besides weight saving. The first is to reduce the effect of welding/brazing which can affect the metal structure and weaken the tube. The second is to improve the ride or feel of a frame, I think particularly with aluminium, a straight gauge tube can be very uncompliant and give an unacceptably harsh ride but by clever use of butted tubes a much more pleasant ride can be achieved.