Genuinely interested x 2.
Extracts from "Bicycle Frame" Wikipedia:
"Stiffness (or
elastic modulus) can in theory affect the ride comfort and power transmission efficiency. In practice, because even a very flexible frame is much more stiff than the tires and saddle, ride comfort is ultimately more a factor of saddle choice, frame geometry, tire choice, and bicycle fit. Lateral stiffness is far more difficult to achieve because of the narrow profile of a frame, and too much flexibility can affect power transmission, primarily through tire scrub on the road due to rear triangle distortion, brakes rubbing on the rims and the chain rubbing on gear mechanisms."
"While many riders claim that steel frames give a smoother ride than aluminum because aluminum frames are designed to be stiffer, that claim is of questionable validity: the bicycle frame itself is extremely stiff vertically because it is made of triangles. Conversely, this very argument calls the claim of aluminum frames having greater vertical stiffness into question."
"Titanium is perhaps the most exotic and expensive metal commonly used for bicycle frame tubes. It combines many desirable characteristics, including a high strength to weight ratio and excellent corrosion resistance. Reasonable stiffness (roughly half that of steel) allows for many titanium frames to be constructed with "standard" tube sizes comparable to a traditional steel frame, although larger diameter tubing is becoming more common for more stiffness. Titanium is more difficult to machine than steel or aluminum, which sometimes limits its uses and also raises the effort (and cost) associated with this type of construction."
and from
Sheldon:
Vertical stiffness
"(Since this article deals with frames, the issue at hand is road shock transmitted from the rear tire to the saddle. Ride qualities experienced at the handlebars are to a large extent determined by the fork, as well as geometry, and flex in other bolt-on parts, but are unrelated to the choice of frame material.)
Much of the commonplace B.S. that is talked about different frame materials relates to imagined differences in vertical stiffness. It will be said that one frame has a comfy ride and absorbs road shocks, while another is alleged to be harsh and make you feel every crack in the pavement. Virtually all of these "differences" are either the imaginary result of the placebo effect, or are caused by something other than the frame material choice.
"Bumps are transmitted from the rear tire patch, through the tire, the wheel, the seatstays, the seatpost, the saddle frame, and the saddle top. All these parts deflect to a greater or lesser extent when you hit a bump, but not to an equal extent.
"The greatest degree of flex is in the tire; probably the second greatest is the saddle itself. If you have a lot of seatpost sticking out of a small frame, there's noticeable flex in the seatpost. The shock-absorbing qualities of good-quality wheels are negligible...and now we get to the seat stays. The seat stays (the only part of this system that is actually part of the frame) are loaded in pure, in-line compression. In this direction, they are so stiff, even the lightest and thinnest ones, that they can contribute nothing worth mentioning to shock absorbency.
"The only place that frame flex can be reasonably supposed to contribute anything at all to "suspension" is that, if you have a long exposed seatpost that doesn't run too deep into the seat tube, the bottom end of the seatpost may cause the top of the seat tube to bow very slightly. Even this compliance is only a fraction of the flex of the exposed length of the seatpost."
