stiffness levels

[steel515]

Anyone ordered a Serotta in very stiff version? How stiff compared to others you've tried? (stiff carbon, cannondale, etc) I assume even very stiff versions would be relatively comfortable compared to aluminum frames.

[dave thompson]

Stiff isn't always good, it can work against you. Certain aspects of a bike should be stiffer than others and depending on the use, there is such a thing as too stiff.

[dd74]

Is there a "very stiff version?"

[dd74]

Stiff isn't always good, it can work against you. Certain aspects of a bike should be stiffer than others and depending on the use, there is such a thing as too stiff.
Correct. And since carbon has no give, isn't it a matter of how many fibers are in the layup that make it stiff or not as stiff; or something like that?

My carbon, off the shelf frame, is stiff, but not uncomfortable. It's definitely not steel, which has a much different sort of comfort/stiffness/ride than carbon.

[dave thompson]

Is there a "very stiff version?"
Serotta can build a bike to suit anyone, from Marty Nothstein (world track and Olympic champion who put out enough watts to light a small city) to old guys like me. Marty would like stiff and I wouldn't. Serotta makes their own carbon for their bikes and uses tube combinations to make the bike behave like the rider wants.

[rice rocket]

Correct. And since carbon has no give, isn't it a matter of how many fibers are in the layup that make it stiff or not as stiff; or something like that?

My carbon, off the shelf frame, is stiff, but not uncomfortable. It's definitely not steel, which has a much different sort of comfort/stiffness/ride than carbon.

There's a lot more to it than number of layers. You can vary numerous amounts of variables to add stiffness/compliance where you want it, including the direction of the fiber, the fiber to resin ratio, the type of resin used, the strength and purity of the fiber itself, the weave of the fiber, etc etc.

Whereas on a metal bike you're limited to the properties of the metal and tube configurations and thickness available on the market, carbon really allows you almost limitless options on where to reinforce specific areas of the bike. That's how they get "laterally stiff yet vertically compliant" bikes. ;)

[fogrider]

stiff is good. it just depends on how much power you put out and how heavy you are. I mean if you're light and powerful, you will stand on the pedals and a not so stiff bike will move forward. but if you're strong enough to flex a frame and the power doesn't transfer into acceleration, then its a not good.

my legend ti with dura ace cranks transfers power into forward movement very well. flaring the tubes at the bb was one of the best things serotta did! stand on the pedals and the bike accelerates to 38 mph! (it went faster in years past)

if you want to be comfortable, you're thinking about compliance.

[Fixed]

Stiff isn't always good, it can work against you. Certain aspects of a bike should be stiffer than others and depending on the use, there is such a thing as too stiff.
+1
cheers

[Charles M]

There's a lot more to it than number of layers. You can vary numerous amounts of variables to add stiffness/compliance where you want it, including the direction of the fiber, the fiber to resin ratio, the type of resin used, the strength and purity of the fiber itself, the weave of the fiber, etc etc.

Whereas on a metal bike you're limited to the properties of the metal and tube configurations and thickness available on the market, carbon really allows you almost limitless options on where to reinforce specific areas of the bike. That's how they get "laterally stiff yet vertically compliant" bikes. ;)


I think metal has enough of a range to cover cycling use pretty well for neccesary flex. Like Carbon, Metal can range from noodle to jack hammer. I do agree that the available tuning within a tube set is better when you can spec each carbon tube, but with butting and swaging, metal still has options (some more than others).



To the OP,

Serotta have a better ability than a lot of manufacturers because they dont depend on outside sourcing for tubes... In the freak case you are outside the norm, one way or the other, you can have what you like in less time than it takes a few others to order something custom from a tube maker. Most Custom Carbon guys can get what they need without any sort of problem though.



That said, the common range of tubes ready and in stock can give you a bike as overly-stiff as virtually anything on the market.

There are folks that really have a need for super stiff. most dont, but some do. Rather than speculating that you dont need it, I'll just say Serotta won't fall short versus anyone else in that game.

[dekindy]

Since stiffness probably has nothing to do with efficiency, and it (http://kirkframeworks.com/Flex.htm) doesn't, would there be any reason to specify any more stiffness than is necessary to keep the frame from flexing so much that the brakes rub under a hard acceleration or climb? I don't know how you would specify that. I would speculate that would be enough stiffness to keep the frame from feeling noodly or mushy. But then again, this is the area where I understand the least and would be the most concerned about when trying to communicate the specifications for a frame. There was a thread awhile back that indicated that Seven cycles owners generally complain about their frames are too stiff but they got what the specified. That would be my greatest concern.

[false_Aest]

so far I'm disappointed that no one has made an ED joke.

[dave thompson]

so far I'm disappointed that no one has made an ED joke.
..........lurking............

[veloduffer]

Anyone ordered a Serotta in very stiff version? How stiff compared to others you've tried? (stiff carbon, cannondale, etc) I assume even very stiff versions would be relatively comfortable compared to aluminum frames.

Aluminum frames can be soft (the old Alan and Vitus) or stiff. Same with any material. You want stiffness in the right places and that depends on weight, riding style (spinner vs masher), application (racing vs touring vs sprinting vs climbing).

Sometimes a certain "liveliness" is preferable to "boardy". For example, many folks find steel frames climb better than their own carbon frames, as the steel frame seems to work with the pedal stroke instead of against it; plus it offsets the (minor) weight penalty too.

Using various points of stiffness to optimize performance is true for other types of equipment like skis, golf shafts, etc.

[nahtnoj]

Anyone ordered a Serotta in very stiff version? How stiff compared to others you've tried? (stiff carbon, cannondale, etc) I assume even very stiff versions would be relatively comfortable compared to aluminum frames.

What does "stiff" mean to you?

BB lateral flex? Torsional flex in the front triangle? A harsh ride?

I'm not sure you've asked the question in a way that is going to generate a useful answer.

Which Serotta are you considering? What frames that you've owned previously are you comparing against?

[rugbysecondrow]

What does "stiff" mean to you?

BB lateral flex? Torsional flex in the front triangle? A harsh ride?

I'm not sure you've asked the question in a way that is going to generate a useful answer.

Which Serotta are you considering? What frames that you've owned previously are you comparing against?


That is what I was thinking. What is stiff to a 145 pound rider will feel worlds different to you Jonathan or to me as a 225# rider.

Somebody said it earlier, Serotta will tailor the bike to the rider.

[sg8357]

That is what I was thinking. What is stiff to a 145 pound rider will feel worlds different to you Jonathan or to me as a 225# rider.

Do you have to know the wattage of the rider along with the weight
of the rider to determine stiffness ?
It seems a 145lb pro would experience a bike differently than
a 145lb twice a week rec rider.

[rugbysecondrow]

Do you have to know the wattage of the rider along with the weight
of the rider to determine stiffness ?
It seems a 145lb pro would experience a bike differently than
a 145lb twice a week rec rider.

Good question and I don't have the answer. This is why it is great to work with a fitter like Smiley. He sees how I ride, know how I am built, translates my riding style and needs to bike/builder speak. When purchasing a Serotta, I am sure the shop would work to do the same thing. I can't specificy what I need, I rely on the experts to take my inputs and develop an output. I am simple like that.

[zap]

stiff is good. I mean if you're light and powerful, you will stand on the pedals and a not so stiff bike will move forward. but if you're strong enough to flex a frame and the power doesn't transfer into acceleration, then its a not good.
.


If power doesn't transfer into acceleration, where does it go.

Most folks ride kit that is too stiff. I look at my cycling mates on Cervelos bouncing around and bitching about rough roads as I ride comfortably on my tubular equipped Klein. Mind you fit has something to do with it too but that's another story.

[Charles M]

I knew this was headed that way...


It takes energy to deflect the BB under load (sideways).

If the BB doesn't deflect, that energy goes to the cranks.

If you watch a high speed film of a BB and stays and down tube flexing off line, the biggest portion of that flex is when the pedals are between about 2:oclock and 4:30... then the BB moves back in to place really quickly between 5 and 6:oclock.

That deflection happens at the peak of most folks power production and the return happens very quickly at the point where the least power is being transferred.

The energy is pretty much just lost. That doesn't mean that all of that energy would go to turning the wheel if the bike were stiffer (some of it goes to spoke wind up or twisting the cranks or...), but some of it does. different manufacturers talk about different numbers, but most agree that BB flex is lost energy.


But I don't think it's a massive performance loss given reasonable stiffness is still there. Unless your strapping on a number, it's almost meaningless for all but the worst case noodle frames and there are relatively few of those around anymore.

[benb]

You'd have to have some way of quantifying exactly what you want if you want it really really stiff.

ISTR when I ordered mine they had some kind of scale from 1 to 10 for stiffness and some questions about intended use. I put in a 7 or something and said "Fast rides and racing".

If I stick the bike they delivered on the trainer I can start to see the BB start deflecting noticeably around 250-300 watts seated and less if standing. (I've got one of the Tacx trainers that can hold a wattage level and increases/decreases the resistance as the rear wheel speed changes, that's what I'm basing this on) Is it annoying? Nope, definitely not. But I've rode some much stiffer bikes and I can't really see the advantage. I also find I can't really feel it anywhere as noticeably out on the road. I wouldn't be surprised if a certain amount of flex at the BB keeps the tires from scrubbing as the bike sways or something.

I also don't have real stiff cranks on the bike.. which seems like it can influence how the bike feels in terms of BB stiffness.

If you really knew what you want maybe you can say "I'm X height, Y weight, and I want less then Zmm BB movement at W watts.." But without some way of really driving it home I doubt Serotta is going to build you jack hammer bike even if you ask for it to be stiff.

[rnhood]

I knew this was headed that way...


It takes energy to deflect the BB under load (sideways).

If the BB doesn't deflect, that energy goes to the cranks.

If you watch a high speed film of a BB and stays and down tube flexing off line, the biggest portion of that flex is when the pedals are between about 2:oclock and 4:30... then the BB moves back in to place really quickly between 5 and 6:oclock.

That deflection happens at the peak of most folks power production and the return happens very quickly at the point where the least power is being transferred.

The energy is pretty much just lost. That doesn't mean that all of that energy would go to turning the wheel if the bike were stiffer (some of it goes to spoke wind up or twisting the cranks or...), but some of it does. different manufacturers talk about different numbers, but most agree that BB flex is lost energy.


But I don't think it's a massive performance loss given reasonable stiffness is still there. Unless your strapping on a number, it's almost meaningless for all but the worst case noodle frames and there are relatively few of those around anymore.

Thank you, well delineated and exactly correct. A stiffer BB will make for a more efficient drive train all things being equal, but whether ordinary riders (like us) will realize any benefit is debatable. In fact its not likely. But fortunately, modern carbon layups provide us with stiff drive trains and suitable vertical compliance. We don't need to be concerned about BB flex anymore as its not needed to tame the ride.

[zap]

If you watch a high speed film of a BB and stays and down tube flexing off line, the biggest portion of that flex is when the pedals are between about 2:oclock and 4:30... then the BB moves back in to place really quickly between 5 and 6:oclock.


The energy is pretty much just lost. .

Unless one has tweety birds legs, high speed film is not needed. Just look down when hammering but please look down with bike on trainer. Energy does not just disappear.

I bet what folks are feeling with stiffer bb/drivetrain is "snap". I think Dave Kirk wrote it best what might be going on with bb deflection.

[nahtnoj]

That is what I was thinking. What is stiff to a 145 pound rider will feel worlds different to you Jonathan or to me as a 225# rider.

Somebody said it earlier, Serotta will tailor the bike to the rider.

Yep. Whether steel, alu, ti, or carbon a skilled builder can make it a rock, a noodle, or anything in between. But you can't just say "stiff" or "smooth" and expect someone to interpret that.

Technique definitely plays a role as well. My Chris Chance has absolutely no torsional stiffness, so I steer it by flicking my hips. My CAAD9, while not the stiffest bike ever, requires a more hands on approach to getting around a corner. Some of this is geometry, but some is just knowing what the bike will respond best to.

Edit - and despite the differences, they are indisputably race bikes. Both models have been on the roof of Mavic neutral support cars. In the case of the Chris Chance, I suspect it quite literally was.

[Charles M]

Unless one has tweety birds legs, high speed film is not needed. Just look down when hammering but please look down with bike on trainer. Energy does not just disappear.

I bet what folks are feeling with stiffer bb/drivetrain is "snap". I think Dave Kirk wrote it best what might be going on with bb deflection.


I want to make sure that others understand that's not what I was getting at.


Bottom line is that the energy that moves the BB off line would generally be applied to pushing the crank in the direction that generates drive force.


The bb returning to center at a point when the power application is far lower is just lost energy. It gets explained away as snap or bounce or return rather than more accurately saying "Lost".


again, take that in the complete context of my post as far as ultimate performance lost...

but BB flex is generally power lost rather any sort of equal / proportional energy returned to driving the bike forward

[Joachim]

Dave Kirk has an interesting take on stiffness and flex on his website. In addition he says energy can't just be "lost". That goes against the fundamentals of physics. Anyway, as long as we all talk about the same thing...

[rugbysecondrow]

I can't discuss the physics of it or the build perspective of it, but I can climb hills seated in my Custom Bedford that I had to be out of my saddle to conquer in my used serptta concours. When i step on the pedal, it goes. No knock against the Concours, it was not made for me. My custom works well and I feel my power is being more efficiently applied out the rear end vs it being redirected or lost. Having read Kirks blog, which I won't try to explain as I would butcher it, but the jist was that a builder must strike the balance that works for the rider between all the forces at play.

It is relative to the rider and Serotta can build to suit your needs.

[benb]

I don't really buy that an stiffer BB is somehow sending more power into the chain. I think people who believe stiffer is "better" have just as much of a need to justify this with physics as DK would need to justify his idea that the energy is not lost.

I am not a mechanical engineer so my understanding of physics may be off here...

You can represent the force from your leg as a vector at every point in the pedal revolution. If you break that vector into it's components there is a force that is parallel to the chainrings which can produce angular acceleration in the chainrings. The other component is going to be parallel to the BB axis.

The stiffness of the frame is going to produce the opposing force that counteracts that component of the riders power which is acting along the BB axis.

Can someone explain how you jump to the sideways forces being redirected to produce additional force parallel to the chainrings on the stiffer frame?

For explanation purposes assume an infinitely stiff frame that cannot be moved at all..

My guess is it doesn't matter how much the BB moves until it moves enough that it disrupts the biomechanics of the riders ankle/knee/hip enough to cause him or her to have to compensate for it by firing stabilizing muscle groups. I find Dave's explanation to make more sense. I wouldn't be surprised if an extremely strong rider on an extremely strong frame just causes the entire bike to rock back and forth laterally as opposed to the frame bending.

If the entire frame is rocking back and forth laterally when the bike is not in a trainer that would provide an explanation for seeing extra BB flex when riding on a trainer as well.

[rugbysecondrow]

As a heavy rider who can crank a little bit, it matters. I, like you, can't explain how, but that is why there are experts to help make the bike do what we want it to and build it to be used like it was intended.

I don't really buy that an stiffer BB is somehow sending more power into the chain. I think people who believe stiffer is "better" have just as much of a need to justify this with physics as DK would need to justify his idea that the energy is not lost.

I am not a mechanical engineer so my understanding of physics may be off here...

You can represent the force from your leg as a vector at every point in the pedal revolution. If you break that vector into it's components there is a force that is parallel to the chainrings which can produce angular acceleration in the chainrings. The other component is going to be parallel to the BB axis.

The stiffness of the frame is going to produce the opposing force that counteracts that component of the riders power which is acting along the BB axis.

Can someone explain how you jump to the sideways forces being redirected to produce additional force parallel to the chainrings on the stiffer frame?

For explanation purposes assume an infinitely stiff frame that cannot be moved at all..

My guess is it doesn't matter how much the BB moves until it moves enough that it disrupts the biomechanics of the riders ankle/knee/hip enough to cause him or her to have to compensate for it by firing stabilizing muscle groups. I find Dave's explanation to make more sense.

[benb]

I'm with you that it feels better.. (I'm not necessarily heavy but I'm on the larger side for a rider)

I just don't believe it actually makes us any faster unless it has something to do with your body not being able to push as hard if your foot is out from under your hip.

I think the two frames transmit the same % of the power, but maybe your body is willing to push harder against the stiffer frame.

It's like doing a squat on an icy surface.. you sure as hell aren't going to be able to lift as much weight if one of your feet starts sliding out from under you.

[rugbysecondrow]

I'm with you that it feels better.. (I'm not necessarily heavy but I'm on the larger side for a rider)

I just don't believe it actually makes us any faster unless it has something to do with your body not being able to push as hard if your foot is out from under your hip.

I think the two frames transmit the same % of the power, but maybe your body is willing to push harder against the stiffer frame.

Like I wrote earlier, I can't speak to faster as I don't have time trial times for both bikes, but anecdotally, I can crest hills faster and seated and more efficiently on my custom, more stiff bike. My concours was nit custom to me and it was labor sometimes. Seated wasn't even an option and out of the saddle, I can feel a distinct different in reaction. I cant explain the inputs only the outputs but it matters.


Anyway, I am fortunate that Kelly Bedford did what he did to make this bike work the way it did. It just works, but I doubt it would be as good a fit for somebody six two and only 155 pounds verses my 230.

[salem]

Do you have to know the wattage of the rider along with the weight
of the rider to determine stiffness ?
It seems a 145lb pro would experience a bike differently than
a 145lb twice a week rec rider.

Wow, this question was tailor made for me, a retired 145# pro! (Caveat: not road, but mountain bike.) Of course, at one time, I rode less (unlike across the pond, most US pros are actually born as amateurs), so I may even be able to cover both sides.

Ultimately, I'd say the weight of the rider is more important than strength regarding frame stiffness. Because I have less mass resisting forward movement, combined with the concept of equal and opposite forces, if I push down harder, there is more inclination for the bike to go forward rather than flex as compared to a heavier rider pushing down with the same force.

As an aside, a frame, fork, or component has to be really flexy (like first generation SPOX wheels) for me to notice it unto itself, however, I easily notice a decrease in flex that occurs with the changing of a part.

To shift to another aspect of the discussion, I'll second or third the idea mentioned that any material can be designed for flex or stiffness. Tubing diameter plays a huge factor. Example: my current Ti frame is significantly stiffer than the Al frame is replaced.

Lastly, if you peek at the current Surly Long Haul Trucker discussion elsewhere in the forum, you'll find an example of a frame that some (myself among them) found too stiff to offer a pleasing ride.

[rice rocket]

Dave Kirk has an interesting take on stiffness and flex on his website. In addition he says energy can't just be "lost". That goes against the fundamentals of physics. Anyway, as long as we all talk about the same thing...
Correct, the energy isn't lost, the energy is put into flexing the frame, which is converted into heat. :)

[HenryA]

I think too stiff a bike is more of a problem than too soft. (within reason) A great bike keeps the wheels on the ground. Really stiff frames and wheels get skippy when you're crankin' hard and/or on rough surfaces. I want the rubber --ON-- the pavement at all times.

If you're buying a new Serotta let them know what your performance expectations are and then let them deliver the right bike to you. Don't just order the stiffest they can make because that's what you think. Make use of their experience building bikes. That's the reason you're having them make you a bike.

[HenryA]

Correct, the energy isn't lost, the energy is put into flexing the frame, which is converted into heat. :)


Yeah, when I ride real hard my frame starts glowing. Melted the BB shell out of one once.

:D

[zap]

I can't discuss the physics of it or the build perspective of it, but I can climb hills seated in my Custom Bedford that I had to be out of my saddle to conquer in my used serptta concours. When i step on the pedal, it goes. No knock against the Concours, it was not made for me. My custom works well and I feel my power is being more efficiently applied out the rear end vs it being redirected or lost. Having read Kirks blog, which I won't try to explain as I would butcher it, but the jist was that a builder must strike the balance that works for the rider between all the forces at play.

It is relative to the rider and Serotta can build to suit your needs.

I've owned lackluster ti frames with next to no snap and carbon kit that would delight trackies with all the snap in the world. The difference in snap (for lack of a better term) is noticable but with day to day variences in mood, energy levels, etc. I could not honestly say that I stood more or less to go over hills between the noodle an d the anvil. But everyone is different.

Speaking to a certain builder a few weeks ago made me think about this whole just right frame stiffness more.