Originally Posted by taras0000

SLX flexes "a lot" because of it's diameter. Steel tubes featured in lugged construction all had to conform to certain external tube diameters to fit into the lugs available. Those diameters are relatively small compared to what is available today in steel, aluminum, or carbon. That's why it seems puny. SLX is a beefed up version of Columbis SL. It's essentially SL "Xtra". It was meant to be a stiffer version of the steel tubes available at the time it was introduced. Back then, it was as stiff as you could get in a lugged frame. What you see in the photo are reinforcing ribs. The reason the tube has that rifling, (the twisted ribs), is because when a bike flexes, it does so because the individual frame tubes twist. If you can align these ribs with the twisting forces, (to put the ribs in either compression or tension), you will best be able to make use of these minimal reinforcements. This is the exact same principle used in orienting carbon fibers within a frame lay-up. Back then, they knew the frame tubes twisted, but they didn't know exactly to what degree, or the force lines, so the twist rate of the rifling in SLX is just a guess as to what would work best.