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Ti bikes are flexy?

Old 07-07-05, 10:19 AM
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whitemax
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Ti bikes are flexy?

I have heard that ti bikes are not as stiff as what I am currently riding which is aluminum. I would like my next bike to be one that will last a long time but which is also fast and fun to ride. Question: Are there ti bikes out there that are known to be stiffer than others? Are there major brands that are known to be flexy is the bottom brackett area that I should stay away from. Recommendations for a good stiff bike of ti would be greatly appreciated.
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Old 07-07-05, 10:35 AM
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Stiffer? Litespeed Ultimate perhaps?
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Old 07-07-05, 10:48 AM
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Stiffness is a relative term. Some people think the stiffer the frame the faster it will be but this is not true; bottom bracket flex on the downstroke will be returned on the upstroke thus no energy will be lost. Further, a frame that is super stiff in the bottom bracket and back end will tend to cause the rear wheel to skip around when sprinting. This skipping around tends to scrub rubber off the tires which will cause more energy loss than flex in the frame.

As far as Ti frames go, some are stiff and some are flexy. The down tube is the more important tube leading to bottom bracket stiffness. Tall aero tubes have the major axis oriented in the wrong direction to stiffen the bottom bracket - this is no major issue though because the large tube will stiffen "enough" for most mear mortals. For a stiff frame, look for something with a large diameter down tube, hopefully ovalized sideways at the bottom bracket.

The stiffer Ti frames on the market will use a 1-1/2" down tube. Also, straight gauge tubes will be stiffer since they are thicker. I like the TST built frames, like the Colorado Cyclist Percision Plus frames, since they use a large down tube and are not over the top price wise. For killer stiff, Dean sometimes uses a super large 1-3/4" down tube, be careful though, it may be too stiff for smaller riders.

At any rate, don't judge a frame by the material.

Hope this info helps.

Ed

Last edited by Nessism; 07-07-05 at 11:09 AM.
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Old 07-07-05, 11:00 AM
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this is just anecdotal, but I know 2 guys with older ti Colnagos (about 4 years old), who describe them as "noodley", and I know 1 guy with a Litespeed who says it's a stiff rocket!

Robbie McEwen had no trouble winning the green (sprinter's) jersey in The Tour on this Litespeed, so I'm sure they're good stiff for us -- although, he is a little guy



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Old 07-07-05, 11:12 AM
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Since I live in the Appalacian mountains, good climbing properties is another aspect I should mention that would be important.
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Old 07-07-05, 11:15 AM
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I think you misheard whoever was speaking. What they actually said was "Ti bikes are sexy".
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Old 07-07-05, 11:25 AM
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Bottom Bracket / Drivetrain
I believe that this is the most talked about and least understood of the three flexes. You often hear people say that the stiffer the better and that any bottom bracket flex results in a loss of energy. I firmly believe that to be untrue. Let's look at what causes bottom bracket flex and what it leads to.

When a rider pushes down on the pedal he also, for better or worse, pushes sideways. This is because the pedal is off to the side of the bike and is not in the bike's centerline. When the rider pushes down with the right foot the bottom bracket flexes to the left. The common belief is that the energy used to push the bottom bracket sideways is lost forever. I contend that it's not lost, but stored to be returned later. Our physics friends will remind us that energy cannot be created or destroyed. It can be converted to different forms such as heat or light, or it can be stored. In this case the majority of the energy that goes into flexing the frame is stored in the frame itself.

When the bottom bracket is pushed to the side, it stays there until the force that was holding it there is released. So at the top of the pedal stroke the bottom bracket starts its sideways move and at the bottom of the stroke it returns to neutral. In returning to neutral it applies that returned energy to the drive train and then to the road. This flex and return smoothes out our power transmission to the ground, making acceleration smoother and optimizing traction.

So what happens is a frame is too soft or too stiff in the bottom bracket for a given rider?

If the bottom bracket is too soft, it will deflect so far that it doesn't have time to return back to its neutral position before the next pedal stroke on the other side. This will feel inefficient as well as unstable… not a rewarding experience.

If the bottom bracket is too stiff for the rider something very interesting happens. We've all ridden with someone whose rear tire makes lots of scuffing noise when they are out of the saddle. What does that noise come from? When the rider pushes down (and unavoidably sideways) and the frame can't flex and store the energy, something has to give. So the tire loses hold of the pavement, resulting in a sideways scrub. In this case energy from the pedal stroke is lost as the tire slides sideways on the road, neither propelling the bike forward, nor returning energy into the next pedal stroke. So it's easy to see why a frame that is too stiff would be slower. By Dave Kirk.
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Old 07-07-05, 11:31 AM
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Stiff and good quality:

http://www.habcycles.com/teamissue.html
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Old 07-07-05, 11:41 AM
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Originally Posted by jeff800
Bottom Bracket / Drivetrain
I believe that this is the most talked about and least understood of the three flexes. You often hear people say that the stiffer the better and that any bottom bracket flex results in a loss of energy. I firmly believe that to be untrue. Let's look at what causes bottom bracket flex and what it leads to.
.
being a bit of a steel fan (even though I do about half my miles on one of my alu bikes), I tend to believe this theory, but a frame that's too stiff isn't the only reason for rear wheel "skipping".

Tyre choice is a factor: if I use a 20mm rear tyre at 160psi, I have no trouble getting to skip.

But the main thing factor is poor technique: moving bodyweight too far forward when off the saddle allows the back wheel to fly all over the place.
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Old 07-07-05, 11:55 AM
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Most of your examples are out of saddle sprinting, which is the best way to test flexablity. But, isn't a stiffer frame better when your in the saddle, powering through a flat strech of road or up a slight incline. I don't do a lot of out of saddle sprints and at nearly 6' 145 lbs, I'm not going to be a powerful sprinter. I am currently riding an Alu frame and I love how easy it feels to maintain speed on flats and up hills. Just curious how much stiffness affects putting power to the ground in saddle where we spend most of our time.
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Old 07-07-05, 12:23 PM
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It really doesn't make any difference whether you are sprinting or just cruising on the flats while seated. The energy that flexes the bottom bracket sideways returns when the force is removed.

Jeff800's post had it right. Nothing is really lost with the frame flexing (extremely small amounts of energy, too small to even really consider).
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Old 07-07-05, 12:37 PM
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Originally Posted by Point
It really doesn't make any difference whether you are sprinting or just cruising on the flats while seated. The energy that flexes the bottom bracket sideways returns when the force is removed.
Not sure if I buy the bit about the BB flex being returned and reused. At the bottom of the pedal stroke, there's a "flat" spot during the transition from one pedal to the other. I think probably the BB just unflexes when the load is removed, and that energy is lost.

If people were machines and the pedal stroke was a perfect circle, then yeah, maybe I could see some of that energy being returned, but I don't think it's very realistic to assume that we're getting any forward assistance out of that on a typical pedal stroke.
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Old 07-07-05, 12:45 PM
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However, if it or the chain stays & BB flex too much, you can find that it will cause your gears to change....I had this happen on a cheap bianci I had years ago, and had it happen on some of the first trek 5200 carbons. Ti offers a different ride than aluminum or steel. Try it to see if you like it. I went from a Cannodale CAAD 5 to a Litespeed Firenze (thought it flexed too much, but had a much more comfortable ride) to a Litespeed Tuscany. I absolutely love the Tuscany....it seems to climb as well as the Cannondale, but the ride is so smooth......
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Old 07-07-05, 01:22 PM
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Originally Posted by motomickey
Litespeed Tuscany. I absolutely love the Tuscany....it seems to climb as well as the Cannondale, but the ride is so smooth......
I have a Tuscany as well and I agree with the climbing and comfort. I had a Lemond Zurich which I thought was very flexy, but I am a pretty tall guy being 6"2" and 180lbs, but I have no problem with flex on the Tuscany and it is just as smooth if not smoother than the steel bike, but a heck of a lot more responsive.
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Old 07-07-05, 01:49 PM
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Originally Posted by cydewaze
Not sure if I buy the bit about the BB flex being returned and reused. At the bottom of the pedal stroke, there's a "flat" spot during the transition from one pedal to the other. I think probably the BB just unflexes when the load is removed, and that energy is lost.

If people were machines and the pedal stroke was a perfect circle, then yeah, maybe I could see some of that energy being returned, but I don't think it's very realistic to assume that we're getting any forward assistance out of that on a typical pedal stroke.

The bottom bracket sways out on the down stroke and then returns to center by itself when the load is removed; net result is no energy loss. The only way energy could be lost is if it's converted to another form of energy such as heat. Simple physics.
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Old 07-07-05, 01:57 PM
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The bottom line is you can make a bike out of any material (cf/ti/al/steel) and it can be either stiff or flexy. So much depends on the way the frame was built. Also using a pro as an example isn't a good way to determine how good a frame is. Many of these frames are custom built for pro riders and most of these guys weigh about as much as a fly's wing.
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Old 07-07-05, 02:05 PM
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I had a litespeed classic that was annoying in that flex in the BB caused quite a bit of front der chain rub. I tried a diff der, and didn't solve my prob. I've since switched to a steel road bike, and haven't looked back.
This is just an example though, others I ride with have and continue to have good luck with their ti bikes (including another Litespeed classic). Goes to show, this really depends on a lot of things.
Being that your shopping for ti, (and are perhaps aware of the related expense) - have a ti bike custom built to suit your needs - ie "not flexy".
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Old 07-07-05, 02:06 PM
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Originally Posted by jeff800
Bottom Bracket / Drivetrain
I believe that this is the most talked about and least understood of the three flexes. You often hear people say that the stiffer the better and that any bottom bracket flex results in a loss of energy. I firmly believe that to be untrue. Let's look at what causes bottom bracket flex and what it leads to.

When a rider pushes down on the pedal he also, for better or worse, pushes sideways. This is because the pedal is off to the side of the bike and is not in the bike's centerline. When the rider pushes down with the right foot the bottom bracket flexes to the left. The common belief is that the energy used to push the bottom bracket sideways is lost forever. I contend that it's not lost, but stored to be returned later. Our physics friends will remind us that energy cannot be created or destroyed. It can be converted to different forms such as heat or light, or it can be stored. In this case the majority of the energy that goes into flexing the frame is stored in the frame itself.

When the bottom bracket is pushed to the side, it stays there until the force that was holding it there is released. So at the top of the pedal stroke the bottom bracket starts its sideways move and at the bottom of the stroke it returns to neutral. In returning to neutral it applies that returned energy to the drive train and then to the road. This flex and return smoothes out our power transmission to the ground, making acceleration smoother and optimizing traction.

So what happens is a frame is too soft or too stiff in the bottom bracket for a given rider?

If the bottom bracket is too soft, it will deflect so far that it doesn't have time to return back to its neutral position before the next pedal stroke on the other side. This will feel inefficient as well as unstable… not a rewarding experience.

If the bottom bracket is too stiff for the rider something very interesting happens. We've all ridden with someone whose rear tire makes lots of scuffing noise when they are out of the saddle. What does that noise come from? When the rider pushes down (and unavoidably sideways) and the frame can't flex and store the energy, something has to give. So the tire loses hold of the pavement, resulting in a sideways scrub. In this case energy from the pedal stroke is lost as the tire slides sideways on the road, neither propelling the bike forward, nor returning energy into the next pedal stroke. So it's easy to see why a frame that is too stiff would be slower. By Dave Kirk.

Thanks for the post. Count me in as another believer.

I own an all Alu. bike (Specialized Allez Elite), and last year I bought a steel/carbon Bianchi Virata. It is easy to tell that the Virata is more flexible in the BB. But, it was also obvious that I could maintain speed much easier on the Virata than the Elite. I kept going through it in my head, and even tested them several times back to back thinking it was all in my mind. I finally came to the conclusion that the flex in the BB gave me extra energy and smoothness when crusing at a given speed. So, not only am I more comfortable, but I'm faster too . I am not taking anything away from the Allez Elite... it's a great bike, but the Virata is better for me (and it should be considering the price difference ).

I considered creating a thread on the subject, but was afraid that I would get laughed at since I have no scientific data. Now I don't have to!
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Old 07-07-05, 02:12 PM
  #19  
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Flexy? No, I wouldn't say it is at all. Responsive, yes.
I have the litespeed siena and I'm really impressed so far.
I will say the entry level Firenze has a much different feel, I described as "squirely".
I'm also coming from riding steel. So when I demo'd aluminum I wasn't at all impressed.
It's all relative. I can that this bike feels different today than the first day I rode it. It's growing on me.
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Old 07-07-05, 02:47 PM
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Originally Posted by Nessism
The only way energy could be lost is if it's converted to another form of energy such as heat. Simple physics.
If you are flexing the frame, you ARE creating heat. Like you said, simple physics. I don't know how significant the heat created is, but it's there.

Another way to look at it is as though your chain were made out of rubber. The chain would stretch when you applied force and return that energy when the force was less. Yes, that would even out the force distribution, but it would also cause the power portion of the stroke to go faster and the dead portion to go slower, kind of the opposite of Bobby Julich’s oval chain rings. I don’t think that would be desirable.

Bottom line, materials aren’t flexy, frames are. After all, aluminum has the lowest modulus of elasticity of the three materials, yet frames made from aluminum are generally considered stiff.

Here’s an article on the subject: http://www.sheldonbrown.com/frame-materials.html

-murray
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Old 07-07-05, 03:12 PM
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My generic Ti TSI is as damn solid as a bike you can fint. Ti flexy...my a$$
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Old 07-07-05, 03:13 PM
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oops........

Last edited by samp02; 07-07-05 at 04:03 PM.
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Old 07-07-05, 03:52 PM
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Originally Posted by Murrays
If you are flexing the frame, you ARE creating heat. Like you said, simple physics. I don't know how significant the heat created is, but it's there.

At the risk of sounding like a know it all...I DO KNOW how significant the heat created is, and it is NOT SIGNIFICANT. Basically, the frame does not increase in temperature enough to be measured thus energy dissipation is insignificant.

There's a reason springs are made from metal, they don't dampen the motion in a significant way. For that, you need a damper. Soft polymer materials, like rubber, do provide some damping. Carbon fiber also provides some damping, but not enough to affect the subject at hand.

I can accept that a flexi frame in the hands of a strong rider is not the way to go. But for the most part, the stiffer is more efficient mantra is BS.

That said, my favorite frame right now is a stiff super oversize custom; the frame rides a little choppy but I love the lack of flex in the bottom bracket. I'm not worried about loss of energy but rather, I hate chain rub and the stiff frame takes care of business.

Ed
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Old 07-08-05, 08:33 AM
  #24  
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If you are interested in a stiff ti frame, take a look at the Litespeed Vortex, you wont be flexing that frame much and it is suprisingly comfortable too (at least my 01 model is). I live in Asheville,NC so i know what you mean by wanting a good climbing bike.
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Old 07-08-05, 08:52 AM
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Originally Posted by Nessism
The bottom bracket sways out on the down stroke and then returns to center by itself when the load is removed; net result is no energy loss. The only way energy could be lost is if it's converted to another form of energy such as heat. Simple physics.
So you're saying it takes no energy to flex the bottom bracket to the side? I think I disagree.
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