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Old 08-09-22, 07:32 PM
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Originally Posted by Kilroy1988
Ah, right, that's why all of today's pros ride on the stiffer carbon fiber frames too and how almost every review of classic steel bikes I've seen by professional riders and journalists who are used to riding on carbon fiber these days specifically mention how their average times over set distances decrease and they notice in particular that their efficiency sprinting or climbing suffers... It's because they don't know how to use their power like in days of yore! Thanks. Very helpful.

-Gregory
Well your dismissive tone makes it seem like you're not interested in seriously considering the other side, and that's OK. You can't go too far wrong riding the same bikes the pros ride. And the stakes aren't very high for most of us, so it's not like we need a once-and-for-all answer to this question, to put it to bed. I just find it intellectually stimulating to speculate on it, with no real benefit in sight. I'm funny that way.

But consider this scenario:
  • Lightness is what sells bikes, and for physics/geometry reasons it's easier to make a lighter bike that's still durable (fewer warranty returns) if you make it stiff. In most cases if you try to design in some flex, it will make the frame either weaker or heavier.
  • All manufacturers face this quandary, and to buck the tide and make a flexy carbon frame (again, probably at least a little heavier and/or weaker) would probably be suicide in this market. So regardless of whether there's some tiny pedaling efficiency improvement to be had from some engineered-in flex, no one is going to try it.
  • Pro racing exists to sell product. Pro racers ride and praise whatever frame they're told to. One guy won several (5 I think) national championships, and raced in two Olympic Games, on a steel track frame I made. It was painted and decaled as three different brands of bike depending on what team he was on that year. In each case, he praised his bike sponsor as The Best, because he was a professional (I think they're literally contractually obligated) Including when his team was sponsored by Merlin — his steel frame was painted to look like titanium, with Merlin decals on it! So that year, Merlins were The Best! Merlin had tried and failed to make him a frame that was stiff enough for him. (Yeah, I can make stiff frames too, I'm not "all about flex"!)
  • Pro racers also often don't know what they're talking about, not educated or interested in science/engineering. Nothing wrong with that, it's not their job. Greg Lemond himself, in a book (maybe ghost-written) said the main thing you want in a race bike is for it to be as stiff as possible. He had been given one superlight flexy undersized steel frame after another throughout his career, and had probably never ridden a stiff frame in his life, so how would he know? And on World Championships race day, of the two frames his mechanic had prepped for him, he chose the more flexible one, likely without even knowing it was more flexible. Maybe he'd have won on any frame (quite likely!), but the flex in his whippy TVT at least didn't prevent him from winning. I think this shows the differences in efficiency due to frame flex, if any, are small compared to other more important factors.
  • Bike reviewers and journalists are famously ignorant of science/engineering (yes there are exceptions), but they sure as heck know which side their bread is buttered on. A reviewer who tried to buck the tide and consistently praise a different kind of bike than the pros ride wouldn't last long in the biz. Magazines don't exist to find the truth, they're there to sell more magazines (and the products advertized therein). "It is difficult to get a man to understand something, when his salary depends on his not understanding it." ― Upton Sinclair
  • Consumers have been told so many times by magazine reviewers and manufacturers that stiffer is better, that they don't even know that it's controversial. Which causes a feedback loop, making the magazines even less likely to "teach the controversy". Actually educating their readers wouldn't help them sell more magazines, it would just piss off a large segment of their readers whose minds are made up. Ain't gonna happen, even if a magazine had a writer/editor who was educated enough to know there's a controversy, and such writers are rare in cycling journalism.
  • Consumers and pro racers alike are prone to placebo, and confirmation bias. These are not small effects, they can easily swamp any actual differences in efficiency. When a riders say they "notice in particular that their efficiency sprinting or climbing suffers", we can pretty much discount this, by around 100%. We know we're talking about differences that are too small to feel. Numerous experiments have shown that human perception of small differences is amazingly unreliable. Jim Papadopoulos (a PhD professor of mechanical engineering who's specialized in bicycles for decades) and a couple of his grad students did a controlled experiment where experienced riders were given bikes that weighed 5 lb more or less and asked to try to determine which they were on, by riding alone. They usually thought they could tell, but their results were 50-50, equal to a coin toss. Five pounds! Think you could beat those odds? Maybe, but can you explain how these anonymous riders you cite could notice their efficiency suffer? The difference has to be quite large before we can trust human perception alone, and I don't think we're talking about such large differences. Placebo and confirmation bias can easily explain those "perceptions".
  • Lowering times for set distances could be caused primarily by frames gettinng stiffer, but for that to be true the added efficiency from stiffness would have to large enough to swamp the improvements from aerodynamics, training and medical science (including doping). Not to mention smoother roads, and increased world-wide popularity of cycling bringing in larger numbers of athletes, including from countries that don't have a long history of bike racing at a high level. Pogacar and Roglic coming from Slovenia, Meintjes from S.Africa for some recent examples, or Froome from Kenya. There's a lot of money to be made as a pro cyclist these days, and it appears that some athletes who would have gone into say football in years past are getting on a bike instead. Less chance of Chronic Traumatic Encephalopathy (CTE) too.
The scenario I just laid out isn't necessarily true, but it's consistent with the evidence you mentioned.

If it sounds like I've made up my mind and can't be convinced otherwise, I'd tend to disagree, at least I think I'm open to real evidence. It's just a hard question to test scientifically.

On the old Hardcore Bicycle Science mailing list (active from a few years before the turn of the millennium to a few years after), a lot of top luminaries from the bike biz and academia tried to tackle the question, without coming to any consensus. The moderator was Jim Papadopoulos, the guy I mentioned with the 5 lb perception experiment. Later, Jim turned the list moderator reins over to Sheldon Brown. Others who took part included Keith Bontrager, Jobst Brandt, Damon Rinard, John Olsen, Gary Klein, John Allen, Doug Roosa and Andy Ruina. A few dozen people total I think including yours truly, under a hundred for sure. But none of these smart guys could come up with any solid evidence one way or the other to prove that frame flex affects pedaling efficiency, either way. Though there wasn't a vote taken, it was clear there was a majority leaning towards some version of "SOME flex is probably beneficial" or put another way, an infinitely stiff frame (if that was possible) would likely be a little slower. Clearly there can also be such a thing as too much flex, and where the sweet spot is (if there is one) will definitely vary from one rider to the next. I think everyone agreed on that.

So, I'm not saying I have proven any case here, just pointing out that the "Stiffer is Better" crowd haven't proven their case either. All the evidence they point to can be explained by other, unrelated effects. I hope we get a real answer someday, but I am pessimistic; I think it'll always be overhsadowed by bigger effects, and dogged by social/business problems that prevent even serious discussion of the question.

Mark B
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