Road Cycling - Frame flex, an interesting subject.

Controversial too. Frame builder Dave Kirk gives his 2 cents on frame flex. What I find interesting about his take on flex is that he was the builder, while he worked for Serotta, of the fabled 7-11 team bikes our guys used in the European pro races and Tours in the '80s. The bikes were built to the riders specs and desired qualities. According to Kirk, all of them wanted some degree of 'flex' in their frames. Nowadays the marketing and oft-parroted buzz-word is 'stiff'.

Kirk's website thoughts on frame flex: http://www.kirkframeworks.com/Flex.htm

All frames flex, that's no secret, it's just a matter of what degree and how well they can take flexing over a period of time.

If you want too see how they test flex... (www.cannondale.com/bikes/innovation/caad7/)

Engineers call it "frame deflection" but it's the flex you have that is lost energy in pedaling.
Click on "testing"
Click on EFBE (****) approved..
In this section is a red box that shows "chart" and you can see how a few frames stack up. You'll be suprised.
Carbon is said to be "stiff'. I call it "dead feeling" but you'll see it flexs more than aluminum Optimo. And titanium flexs more than either...

fyi...

Noting really interesting or new here - pretty straight forward, common sense stuff.

I think what was interesting in the Cannondale link was that BB deflection between the tested frames was only ONE MILLIMETER! Now what I want to know, is how much deflection the cranks, wheels and tires deflect when pushed sideways.

Only 4% of your effort is pumped into the frame, I wonder how much the components contribute to 'power loss'?

Dave Kirk is correct though - it's about creating a harmonious dynamic structure that is comfortable and efficient. The sooner people realise that 'Stiffness is not next to Godliness', the better.

Noting really interesting or new here - pretty straight forward, common sense stuff.

I think what was interesting in the Cannondale link was that BB deflection between the tested frames was only ONE MILLIMETER! Now what I want to know, is how much deflection the cranks, wheels and tires deflect when pushed sideways.

Only 4% of your effort is pumped into the frame, I wonder how much the components contribute to 'power loss'?

Dave Kirk is correct though - it's about creating a harmonious dynamic structure that is comfortable and efficient. The sooner people realise that 'Stiffness is not next to Godliness', the better.

That's why I posted this link, I'm of the same opinion as you (and Dave Kirk). I love the 'stiffer for efficient power transfer' hype that often is pushed by marketing types that is oft repeated enough to be perceived as carved-in-stone-fact. There is little, if any 'power' lost if a frame has a slight amount of flex, and certainly having the tires scrub sideways if the frame is too stiff results in lot (relatively) lost power and momentum.

I'm not trying to be flippant but of course it's obvious that you want a well-balanced frame.

As for tire deflection, you can control that to a certain degree since you can control the type and psi of the tire. You can buy stiffer cranks. You can't change the characteristics of a frame.

All I'm saying is that it is all inter-related and this stuff- while interesting and helps Kirk sell excellent bikes- doesn't mean anything. A little bit of information isn't a good thing.

On the other side of the coin, just because a frame has minimal deflection at the BB doesn't mean it's an uncomfortable, unbalanced frame either. You DON'T want a carbon or aluminum frame as "flexy" as a steel frame because of the basic nature of the material.

Rubber tubes would be at one end of the spectrum and Aluminum would be at the other. Aluminum doesn't like to bend a great distance. Neither does carbon.

Then again, within it's designed range, carbon can cycle indefinitely without failure. Steel or aluminum won't.

Then again it also depends on the type of carbon, steel and aluminum. There are levels of each.

What about Ti? There is 6/4 and 3/2.5. So even ti has different characteristics in material content and the way you shape tubes.

The list is endless. In the end, what is important is the final product, all this other stuff is intersting but doesn't mean anything unless it works on the pavement.

Since I don't build bikes, I don't care what the builder does. All I care about is the ride and fit-quality & workmanship, of course. That's where I'll put my money down on.

Never felt it so i dont know what it feels like.

RacerX, you are incorrect about a few things.

Firstly, you say "As for tire deflection, you can control that to a certain degree since you can control the type and psi of the tire. You can buy stiffer cranks. You can't change the characteristics of a frame." Well call me weird, but you can buy a new frame, just as you can buy new cranks or tires. Your comparison makes no sense.

Secondly, you say "Then again, within it's designed range, carbon can cycle indefinitely without failure. Steel or aluminum won't." This comment is totally incorrect. Aluminium has a finite fatigue life - it will brake regardless eventually. One cycle taken is one cycle less it will take in the future. Steel on the other hand has an elastic limit that is nowhere near it's UTS, meaning cycled below it's elastic limit, it will theoretically cycle forever.

Finally, you comment "Since I don't build bikes, I don't care what the builder does. All I care about is the ride and fit-quality & workmanship, of course. That's where I'll put my money down on." How can you say in the one sentence you dont care what the builder does, and 5 words later say you care about fit, quality and workmanship???? You care or you don't, which one is it?

Davet - good to see there's another cyclist with 'eyes wide open'. Thanks for not believeing the Hype.

thylacine,
Nice bastardizing of my post!

You can control a tire's deflection because you can pump it to 100psi or 250psi. That is a controlable variable. A flexy crank or stiff crank-that is a relatively inexpensive variable. A frameset? Is that a realistic variable you can adjust? You start with a solid foundation, meaning a solid frameset. A frame is NOT easily adjustable- you have to replace it and that is just not a alternative to most people.

Carbon can cycle indefinitely without failure (actually it will eventually fail but not in a bicycle's lifetime).
Aluminum has a finite fatigue life? That's what I said!

"carbon can cycle indefinitely without failure. Steel or aluminum won't."
That means: steel or aluminum cannot cycle indefinitely without failure.

On Litespeed's torture machine;
"This machine puts 750,000 cycles on our titanium frame with 400 lbs. of force on the bottom bracket and headtube per cycle.
An aluminum frame will break at 200-300,000 cycles, while a steel one will break at about 400,000 cycles.
A Litespeed Vortex will last between 1 and 1.5 million cycles"


Finally,
I DON'T care what the builder does. They can explain all the science and superstition but what matters is what hits the pavement.
Of course workmanship and quality matter! This entire thread is not about that. This thread started about FRAME FLEX. I am saying I don't care what a builder has to say about it, I care about how it performs plain and simple.

"not believeing the hype" is what you do when you judge a product based on your own testing and the judgement of those you trust. I have said and done that, I think.
I have tried to be honest and forthright with all my comments and hopefully they come across that way or are of some interest anyway.

Steel CAN cycle infinitely. I didn't bastardise anything! :P

Do you have the article on the outcomes of Litespeeds testing? I'd be curious to see what frames they compared and their methodology.

So how does this all relate to a fella that may buy a new bike every, say, 3-7 years, and is not a top competator?

Dont belive everything you read or here.
Dont belive the hype?Does that include litespeed?

So how does this all relate to a fella that may buy a new bike every, say, 3-7 years, and is not a top competator?

Get the bike you like. Instead of obsessing, you can be riding.

So how does this all relate to a fella that may buy a new bike every, say, 3-7 years, and is not a top competator?

I think the bottom line is is that stiffness is not that important. In fact, if you're an enthusiast and you tend to keep you bikes for a long time, it's probably MORE important that you buy a comfortable, well fitting bike. Unfortunately that probably doesnt mean an oversize Aluminium bike with parallel 74 degree angles and 410mm chainstays, which unfortunately is often what we're often lumped with.

Dont belive everything you read or here.
Dont belive the hype?Does that include litespeed?

:lol: Yeah, Litespeed TOTALLY lies about testing frames. Ti REALLY isn't superior in tensile strength, elongation or anything else. It's all hype.

read my post from 02-10-04 at 12:33 AM
...You DON'T want a carbon or aluminum frame as "flexy" as a steel frame because of the basic nature of the material....

...The list is endless. In the end, what is important is the final product, all this other stuff is intersting but doesn't mean anything unless it works on the pavement.


from 02-11-04 at 05:14 AM
"not believeing the hype" is what you do when you judge a product based on your own testing and the judgement of those you trust. I have said and done that, I think.

I am not hyping or pushing anything in my comments. In fact, I am saying the opposite. I am saying let the ride be the judge, not the material.

My steel frame isnt flexy. One person says its the material and another says its the way the frame is made. I say bullsh$t to both and do as you say,let the ride be the judge.