Originally Posted by
Piff
It is stronger, but that's not the same thing as stiffness.
All steel has the same stiffness. Some are stronger, and can be drawn into thinner tubes which will reduce stiffness. Larger diameter tubing will restore stiffness, allowing high stiffness and low weight in comparison to less fancy steel. What reynolds means when they say 853 'allows frame builders to make very strong, stiff frames with a low frame weight' is that the stronger 853 steel can be made into thin/oversize tubing that attains strength/stiffness of smaller diameter tubing that is thicker.
A straight gauge frame of 531 in 0.9mm is stiffer than double butted 0.8mm/0.5mm 853 of the same diameter because the 531 tubing is thicker throughout. But by increasing the diameter of the 853 tubing, you can create a tube that is both stiffer and lighter than the 531. The greater strength of 853 allows for this.
Well, we're talking from two different perspectives here. I agree entirely that "all steel has the same stiffness" if your measurements are identical. However, I am talking from the perspective of a built frame. The stiffness of the frames I've had - and the advertised utility of a frame - made from 853 has in general been greater than my 531 frames. The inherent strength of the frame material allows that to be accomplished.
Please note that in my initial post you quoted I said a "stiffer frame," not "stiffer steel."
-Gregory