Originally Posted by
HTupolev
I'm not saying it's more or less valid than anything else. I'm saying it offers insight as to what people within the bicycle industry are willing/able to test, and in particular the lack thereof.
No, they definitely do test. I'm saying that the testing probably isn't as broad and holistic as you think.
For instance, I would expect that it's rare or nonexistent for racing teams to have a bunch of otherwise-equal copies of a frame made with varying stiffnesse in order to quantify the impacts. That's in the realm of things that are messy and where you can't tweak things for rapid turnaround. And that's the sort of thing that would have to be done to make a useful judgement on the effect of frame stiffness.
Yes.
Stiffness should matter to how a frame behaves as suspension. Plenty of modern frames try to smooth the ride by allowing considerable vertical flex to occur, sometimes adding an explicit damping mechanism to prevent ringing.
That's one area where CF may have an advantage over the metals; it seems like it tends to be a more imperfect spring on its own. Titaniums and steels can often be allowed to flex by a huge amount without durability concerns, although being very undamped, that could cause excessive rebound in some circumstances.
As far as pedaling...
I recently changed the cranks on my gravel bike to test how it would feel if I made the pedal position closely match my road bikes. Not a big change, but slightly narrower Q and slightly shorter arms. However, the new cranks are a bit on the cheap side and doubtless much stiffer than the old ones; both use solid aluminum arms, but the old ones are decent spindly vintage arms while the new ones are very fat. Since that change, which I will soon revert, it's been nigh-impossible for me to stress my cardio on that bike; I simply can't get my lungs to work hard even at very high RPMs, except while climbing. The speeds I can maintain on flat ground are noticeably slower, and my quads fatigue extremely quickly if I try to go fast. It is exactly in line with the sorts of differences described in the results of the BQ frame flex study for when someone's legs weren't liking the characteristics of the bike.
I find the argument that flex about the bottom bracket can be significant in terms of the biomechanical side of the pedal stroke to be pretty convincing, even if the mechanism isn't well-understood.
Hard to say. I'd say that needs further study. Intuitively it seems that increased rider power should play nicely with increased stiffness, although without the effects of frame stiffness being characterized across demographics, and without the mechanisms behind its effects being well-understood, I hesitate to make a particular judgement. Sean Kelly seems to have enjoyed riding a screw-and-glue wet noodle, at any rate.
To me and to use your word, I don't believe most who think of frame stiffness, they don't think of it holistically enough. They think of stiffness in the context of energy transfer only. To me, this is a big mistake. There are many more reasons top manufacturers make their frames stiff.
Do you put out big watts? Ever broken a frame while sprinting? Ever caused your brake pads to rub while sprinting? How about pretzeled a frame so much it shifted a gear? Top racers have this problem. Bicycles aren't just manufactured for you or for me...or a tall skinny boy who can only put out 300 watts in a sprint...but for everybody and top racing frames have to be able to stand 220 lb guys that can put out 2000 watts or almost 3 hp. The world of design isn't an even playing field. Its made up of a broad demographic for different riders even specific to a given frame size.
Hurricanes have been frequent of late and I just lived through one...my first in Florida. If you watch the news maybe you have seen a palm tree that has snapped in two...one with a deep root structure. Many of these trees have been around for decades and even withstood tropical winds in the 50-60 mph range. What happens when a Cat 4 wind comes to these trees that typically bend due to their evolution? They snap. So do frames. Stiffness matters on many levels. There is a reason why some pro's need reinforced frames which makes them stiffer. They can snap with the force they can apply to the pedals that the average guy can only think about.
Control is another big factor as I discussed in a previous post. A rider's ability to control the frame in space while powering the bike matters. Heck...me a guy who can't push even 1000 watts on a bike can sprint faster on a stiff bike versus a noodly bike I am all over the road on because the bike is twisting all over the place which affects the handling and even the chainline. There are guys out there that the same bikes are sold to that put out twice the power I have. I can't even imagine how much a noodly frame would twist with the kind of power they can lay down.
In summary, there are many reasons why top race bikes are made stiff. There is a precarious balance for example between stiffness aka force/deflection, weight and yield strength. Weight is a priority in road bikes of course because lighter tends to be faster...certainly for acceleration and climbing. But if a bike is made too light and relatively stiff, it can crack like a pane of glass. The UCI weight limit in fact came about as a safeguard to bicycle safety...because a stiff 10 lb bike may crack in half made out of modern material with a 2000 watt sprinter on board.
Testing isn't momentary. Data bases aren't instantaneous....or can be but buttressed with years of data. Riders known anecdotally what kind of frame works best for them as they experiment throughout their riding lives until they come across a bike they are faster on. Race bikes are stiffer because they are faster. A broken bike isn't fast. A bike that is twisting all over the place a rider can't control isn't fast. A bike where the brakes rub isn't fast. A bike that unintentionally shifts gears in the middle of a sprint isn't fast. Stiffness is about control, safety, durability and arguably more efficient energy transfer. But there is a reason why many doubt that stiffness matters. Because they don't put out much power and riding a bike to them and me is like a grasshopper versus a sumo wrestler jumping on a swimming pool diving board.