ShannonM

There's a meme (in the original sense of the word, a unit of cultural heredity, not the modern stupid-picture-of-a-cat-with-a-stupid-saying-in-white-letters sense,) that has been replicating in the brains of humans who ride bicycles for many, many years... and it's nonsense.

That meme is this:

Flex in the bicycle dissipates some fraction of the force generated by the rider's muscles.

This is simply, physically, not true. The thing that it's describing does not actually happen. Numerous attempts have been made to measure this "power loss." So far as I'm aware, nobody has ever been able to repeatably detect any power loss due to bicycle flex that is above the noise floor of the equipment used to do the measuring.

And, because the meme isn't actually true, this statement is true:

Unless the bicycle and/or its components are so flexible as to have negative effects on handling, alignment, or durability, the stiffness of any part of the bicycle or the bicycle as a whole is utterly irrelevant to the performance of the bicycle.

Stop caring about the stiffness of your frame, cranks, wheels, stem, handlebar, pedals, brake levers, (yes, I've seen stiffness referred to in brake lever reviews,) or any other part of your bicycle with the possible exception of racks. (And even they're not much of an exception... any rack strong enough for the load you're putting on it will be stiff enough for that load... if it wasn't, it'd break.)

Stiffness does not matter.

--Shannon

Jax Rhapsody

Wow... nobody... just me? Okay...
Stiffness to a degree does matter. Though how loose versus stiff some things are, is marginal, like most cranks, unless the force exerted on a crank makes it flex, especially the chain rings wobble, then it's stiff enough. I've had bikes with various cranks; never has one not felt stiff.

Stiffness differs depending on what. Brake lever stiffness is probably more about how much give it has at it's hinge point, than how much "flex" the lever byitself has.

I had a bike frame break because a makeshift trailer hitch mounted on the chainstay went in the wheel and broke spokes. The wheel made the frame shake so bad, the downtube broke by the BB. The bike was large and somewhat flexy as it was, just mashing on it, the BB was clearly seen swaying left&right, noticably.

Stiffness can mean many things. Would you not want stiff door hinges on your car, or are sagging doors ya gotta lift and slam okay with you? With bikes there are things you don't want flexing, some people just go overboard, sometimes those people don't even know what they're talking about, and the difference between crank a and crank b's stiffness is so marginal, they mentally exacerbate it with a placebo effect. What's stiffer; a 105 crank, or a Seguino Messenger crank? Maybe the Seguino since it's thicker, but the reality is; it's trivial bullspit on something so slight, nobody really knows the difference just by riding with both, but they think they can tell the difference. Like how some people think they can feel that extra 2hp, swapping out the paper airfilter for a Fram on, in their car.

There's a point where stiffness matters, and a point where it's overhyped for clout and whatever. If your bike isn't acting like it's in a Tex Avery, or United Artist cartoon, it's probably stiff enough.

PeteHski

I agree entirely on the "power loss" thing being a load of BS, especially within the range of flex we are typically talking about in practice.

But that doesn't mean stiffness is not important in several other ways i.e. handling and comfort. A frame with poor torsional stiffness will handle like a soggy couch. Bars that are noticeably flexible will not provide solid support when sprinting hard in the drops or climbing out of the saddle. Too much fore-aft flex at the headset and fork can make braking very unstable (try riding with a slightly loose headset and see how that feels when braking hard on a steep downhill). The best frame designs optimise stiffness in specific load directions i.e. combining high torsional stiffness with relatively low vertical stiffness (e.g. D-shaped seatposts, super thin seat stays) to give both precise handling and a reasonably compliant ride. Wheel stiffness, both lateral and vertical, is also important for handling and comfort.

Stiffness certainly matters a lot, just not in terms of power delivery.

cb400bill

Okay. Thanks.

PeteHski

Interesting that you brought up brake levers as an example. I agree, the stiffness of the brake lever is pretty irrelevant given how little force you actually apply to it. But what does matter is the stiffness of the brake caliper at the other end. If the caliper body is too flexible then the brakes will feel mushy.

OldTryGuy

Me thinks the poster might be lacking in age and experience to make such a statement.

PeteHski

Well I'm fairly confident he/she is not working in engineering mechanical design. But they do have a good point about the gross over-statement of stiffness relating to power transmission. It's just that the thread title is grossly wrong for all the other reasons why stiffness does matter.

indyfabz

shelbyfv

OP should contact Trek, Specialized... big money to be made as consultant engineer.

Koyote

This thread title is like a nice easy pitch right down the middle… But I don’t want to get banned.

OldTryGuy

EVEN STILL, a whiff is possible

Here's a MONDAY MORNING interlude for y'all's perusal


NOTE -- mods can delete if inappropriate

Phil_gretz

A $3.6 Billion pharmaceutical market might throw shade on this statement. Just sayin'...

GhostRider62

I'm the wrong kind of engineer to make a decent analysis but I have been riding a long time and like everyone, I have my anecdotal observations.

My best climbing bike is a very stiff Pinarello AK61. When I get out of the saddle in the big dog, it just goes. All of my climbing PB are on that bike.

Long and flexible framed recumbents are dogs when it comes to climbing

What I think happens on a flexy bike is the sideward movement puts a moment onto the tires and this frictional loss is not recovered and it is significant. A stiff frame keeps everything nice and straight and tidy. I could be way off base and BQ planing could actually be the golden goose.

OldTryGuy

I find that figure hard to --- believe.

unterhausen

I have a facebook friend that posts half bike stuff and half memes in French
He posted one that used "meme" in both the French and popular culture senses of the word. It took me 7 hours to get the joke.

freeranger

Guess all the fork manufacturers that built a lock-out in their design have wasted their money? I would think the motion of a suspension fork could qualify as "flex".

Clyde1820

Seems hard to believe that if energy X is put out, but a portion (Y) transmits to downward or twisting motion instead of forward motion, that there has to be a loss. Miniscule, perhaps hard to even measure. But, still.

My own experience is with distance running. Absolutely, if energy is expended with, say, overly-exuberant motion of the arms, or sideways movement (no matter how little) of the stride, it can often be felt via the time for the course, the remaining "oomph" one has left as the race progresses, the difficulty experienced on that route, etc. Measurable? Never have "measured" it, as such. Other than paying attention to what aspects of a run and technique seemed to correspond to tanking, having less apparent strength, feeling winded, etc. Ran a couple tens of thousands of miles, back in the day. And flagging results was frequent enough, when technique was off, that we paid attention to those little things. Efficiency, IOW. No substitute for it. Even if not easily measured.

Phil_gretz

Total market value, 2020, from Mordor Intelligence, an investment analysis firm. Projections are a bit droopy out to 2026, though.

Koyote

With all of those aging boomers, I'm guessing that sales will stay firm.

Hiro11

This is a very old debate and OP is not the first person to mention this. To me the debate over stiffness has always been more about feel than "efficiency": a stiff/snappy bike just feels better out of the saddle or through a fast corner to most riders. Also, I've found that modern materials, tires and engineering have changed this debate. It used to be the case that you had to choose between a stiff handling/responsiveness and comfort, all modern bikes now have lots of both.

Metieval

If you saw a meme , I am guessing it was Facebook, just report it to the FB "fact checkers" and move on.

If the meme was false, I am pretty sure they will flag it as false.

/endsarcasm

Oh btw, stiffness does matter in my world, as it matters to me. To each their own.

thehammerdog

is that what she said?
doooo

indyfabz

"Dookie" (the guy at the computer), whose real name is Scott Brooks, was a childhood friend of mine. We grew up a few blocks away from each other and were members of the same swim club. Very funny and talented guy.

indyfabz

So if a rack needs to be stiff enough so that it does not break under load then stiffness does matter.

Thanks for confirming.

Iride01 

Hard to shoot pool with a rope!