PeteHski

The Specialized Roubaix has a handlebar suspension on top of the headset allowing 20 mm of vertical travel. The latest version of it is sprung and damped. The original didn’t have the damper. They did apparently test a similar system on the seat post but found that riders didn’t like the way it pedalled with vertical compliance (not surprisingly). So they went with a more typical compliant seat post to provide a bit of comfort. Most modern bikes now have fairly flexible seat posts to add comfort. The D-shaped carbon post on my Defy is notably springy, but because it only defects backward it doesn’t affect pedalling.

Paul Barnard

Does this mean that the stupid justification for press fit bottom brackets is gone, and now we can get back to much more sensible threaded BBs?

GhostRider62

Jam hard out of the saddle over a hill with low tire pressure in a flexible frame Repeat with proper pressure. Switch to a stiff frame and repeat.

The losses are in the tires, not in the metal or carbon.

genejockey 

Lots of theoretical handwaving. Not a lot of data.

I can tell you that the stiffest frames I have are the ones the feel best in a sprint or other out-of-saddle effort, while the least stiff don't encourage that kind of effort. However, I'm also always aware of which bike I'm riding, so I can't dismiss expectation as a variable. And in the end, I don't need to because it doesn't really matter whether or not stiffness of the frame 'doesn't really matter' because somebody's got a hypothesis (it's a hypothesis, guys, not a theory).

Hell, I've even been told that stiffness of the frame doesn't matter for comfort and compliance because of some guy's hypothesis, but I still find myself seeking the least bumpy line with some bikes more than others, and some bikes on the same roads kick me up out of the saddle more than others. So I'll stick with my observations, because observation is how you determine whether hypotheses are correct anyway.

KKBHH

I was suggesting that it's the Cannondale Kingpin seat compliance system that should be considered. And I was suggesting to forget about simple handlebar springing. I haven't tested either system.

On second thought, maybe the Specialized 20mm of handlebar springing is the correct amount
.

phughes

If a bike falls outside a convenience store, because it doesn't have a kickstand, and no one is around, does it make a sound?

Maelochs

if Francis Bacon was so smart, why didn't he invent the bicycle?

wolfchild

Steel is the best material for bike frames.

GhostRider62

I prefer my two magnesium framed bikes over all my steel bikes by a large margin.

genejockey 

He invented bacon. Wasn't that enough?

genejockey 

ftfy

Maelochs

Steel is the best material for steel bicycle frames.

Metieval

If you want handle bar compliance, get some abs, start pulling on the bars instead of using them as an upper body support shelf, And quit locking your elbows!



I have a theory on why some people dislike stiff bicycle frames.
Might be time to start riding your bicycle instead of riding on it.

ShannonM

No.

At least not by the US Navy's definition of "sound," the correctness of which I am unsure of to this day, almost 27 years after I learned it in Sonar Technician A-school.

Per Uncle Sam, "sound" is the acoustic energy transmitted from a source, through a medium, to a receiver. Without a receiver, it's just acoustic energy, not sound.

Yeah, it's definitional and nit-picky and almost circular, but it made me giggle when I first heard it, and it still does.

--Shannon

Branko D

What - no. Given the choice, I'm going for pressfit.

The difference between a poorly done PF and an equally poorly done threaded BB on a carbon fiber bike is that the first will creak, the second won't. Both will eat bearings prematurely and waste more power than frame flex possibly could. Adding weight by gluing alloy inserts just so the manufacturer can mask their poor quality control on a multi thousand dollar frame - I'll pass.

ShannonM

This would be the right answer if the manufacturers of multi-thousand-dollar frames could be relied upon to meet the tolerances required to make a low-power, low-rpm press-fit bearing set work reliably.

They have proven over and over again that they cannot.

Despite the fact that every other industry has been using press-fit cartridge bearings for decades, in applications with orders-of-magnitude greater force and speed inputs, the bicycle industry can't make frames that will properly align a pair of bearings to cope with loads of less than one horsepower at 120 rpm without screwing things up. So the only way to get a BB / frame interface that doesn't suck is make the interface adjustable.

--Shannon

Branko D

Well, some manufacturers stick with pressfit and the vast majority of their bikes have no issues. Some have abandoned it in favour of threaded, but personally I hold it against them - to me it screams "we're too cheap to do decent quality control on a multi thousand Eur / USD frame so we're not even going to try". Threaded on a CF frame also can come out crooked - it just won't squeal when it does - so it's really just fixing the symptoms of crap manufacturing tolerances.

Next CF frame I get will almost certainly also have a pressfit BB.

PeteHski

Because they are uncomfortable on rough roads?

PeteHski

Yeah that looks quite effective. Willier have something vaguely similar with an elastomer at the seat stay / seat tube junction (see link below). But for road riding I find that 28-32 mm tyres and a D-shaped relatively compliant carbon seatpost, along with relatively thin carbon seatstays, provide plenty of comfort. It's usually the front end I sometimes find a little harsh. Carbon bars help a fair bit with the vibration and most carbon forks allow some degree of compliance. But I can see why the Roubaix exists for riding cobbles. For riding rough gravel the Cannondale system looks pretty good with 30 mm of compliance. I'm a little surprised they didn't match it with a front suspension, other than a compliant fork. I don't recall many XC bikes having a rigid fork + rear suspension. Quite the opposite!

Edit: One thing about the Cannondale Kingpin I would be concerned about with 30 mm of compliance is damping as it appears to be an undamped spring and that is quite a lot of movement. I used to have a Cannondale Scalpel, which also used flexible chainstays for rear suspension, but it also had a spring/damper at the seatpost junction. The first version of Specialized's Futureshock was also undamped and some people found it too "bouncy". The Mk2 version added a damper, which was considered a significant improvement. But maybe the damping is not so critical at the rear end. The Willier system I mentioned will have a fair amount of natural damping in the elastomer.

https://wilier.com/en/my2022/int/rac...kes/cento10ndr

PeteHski

Talking of compliance, I'm quite intrigued by OPEN's MIN.D road frame with its 25 mm continuous seat tube/mast and wafer thin bowed seat stays. It looks very comfortable to me, without resorting to a more complicated suspension design. Also appears to be stiff in all the right places.

https://road.cc/content/review/open-mind-2020-276793

Metieval

Oh I've seen all kinds of tips for riding rough roads.

Less psi
Relax
Higher gear
Wider tires

I've yet to read any article on how to ride rough roads / cobble stone that suggest buying a bicycle with a frame that is a flexible noodle.

Maybe you know of a few articles that suggest flexible frames?

Milton Keynes

Well he invented bacon so that was a pretty good accomplishment.

PeteHski

There are plenty of road race bikes with targeted vertical frame compliance. Flexible seat posts, seat stays, chainstays, forks, bars etc. It doesn't make them flexible noodles. It's all about directional stiffness.

Metieval

/end thread

Thanks!

Kapusta

I believe your understanding of how the spring (bike frame) is storing and releasing energy is a little off, and the highlighted statement may go to the root of it.

What "direction" the frame appears to be flexing is a red herring. Here is is what is going on:

When you apply force and power through the cranks, the cranks exert a force on the bb shell (and the frame). The frame needs to match that force, otherwise the cranks would not redirect the force of the pedals to the chain. With an infinitely stiff frame, the force would be matched completely with no deflection thus no energy goes into bending the frame. With a real world frame, it deflects until the force is matched. It takes energy to do this, thus you temporarily lose this energy to the spring (frame). The less stiff the frame, the more it needs to deflect to match the force, and the more energy is diverted/stored in the frame.

Now consider what forces on the cranks are causing the crank to exert a force on the frame. 1- The force pushing on the crank arm, and 2- the force of the chain pulling straight back on the top of the chain ring.

When that stored energy is released, it is going to do so in the exact opposite direction (vector). Thus, unbending force of the frame will act on the crank in the exact opposite vector as when the crank deflected the frame, and the crank in turn directs this force in an opposite vector to the to the chain (pulling pulling forward.... thus the drive force) and back into the crank arm (force against you pedaling).

I believe the key as to whether you waste energy (and how much) has to do with how much of that energy goes through the chain and how much back through the cranks (*see caveat below). And honestly, this is where I get a little fuzzy (Perhaps someone else can pick up here) .I believe is has a lot to do with the timing of your pedal stroke in relation the the frequency/timing of the spring - and I am pretty sure that is what the concept of "planing" is all about.

BTW, the example above is just one of the many ways that a frame may be flexing and storing/releasing energy. Here is another: The force on the chain causes tension on the chain that is trying to pull the chainring and cog closer together. Since the chainring and cog are both off-center of the frame, they can get closer to each other by bending the frame between the BB and rear axle. Thus, there is always some bending force on most frames when you pedal. A really stiff frame bends minimally, thus diverting/storing little energy. A more flexible one bends more, thus storing more energy. This is a perfect example of the direction of the frame deflection being misleading. The frame may be bending to the side, but the forces acting on it are along the chain line. And along the chain-line is where this frame/spring is going to return this force (and energy).

*There are also loses due to damping, but that is a different subject. And for metal springs, it is minimal.