|is there such thing as||cyclopathic|
Jan 30, 2002 11:19 AM
|compliant frame with stiff bottom bracket?
tried a bunch of steel frames (LeMond, Bianchi) and while they ride nice it's scary to see BB deflect almost 1" under heavy pedaling
|How's ever tried one of those...||tempeteKerouak|
Jan 30, 2002 11:31 AM
|Ok, out on a limb here...
But, hey! Some assume their stuff and get bashed for it!!! But they still ride their Y-foil-beam things enjoying a drink from a back-pack supported bladder... Some even go as far as riding (dare I say it) mtb pedals AND shoes on the road. (May the wrath of God be forgiving!) And I hope you never see my jersey with the cut out sleeves. Anyway.
They tried oversize tubes, dual downtubes, straight stays, CNC machined bb plates... When it's stiff, it's stiff. When it's smooth, it sways.
Why not get a stiff frame and a really good suspension seat post?
Who ever tried a Cannondale with the lockout front suspension? I could endure that and seat post for a while!!!
Jan 30, 2002 11:41 AM
|You "see BB deflect almost 1" under heavy pedaling"??? Wake up, pal.|
|hey jackass... don't be rude.||mixinbeatz|
Jan 30, 2002 2:07 PM
|I have a bianchi all steel and on a fluid trainer my bb easily sways an inch or more under heavy pedaling. What makes you think that this is not possible?|
|that's me!||Jack S|
Jan 30, 2002 4:00 PM
|...and I ain't buying it either!|
|Excuse me? I believe he was talking to ME.||Jack Ass.|
Jan 30, 2002 4:10 PM
|The man say Jack Ass not Jack S. And I have seen that very thing. True dat. bn mus be one tiny tiny man.|
|I approve of Mr Ass's above statement no message||The Pickle Matrix|
Jan 30, 2002 5:55 PM
|probably the trainer||Dog|
Feb 1, 2002 6:48 AM
|You're probably seeing flex from movement of the skewer in the trainer and flex in the trainer itself. I know mine do it, too. Put the stiffest bike in the world (Cannondale?) in the trainer and it would probably appear the same.
|not many even know what 'compliant' means!||NM|
Jan 30, 2002 11:42 AM
|Back to the question||jtolleson|
Jan 30, 2002 12:06 PM
|Actually, I think it exists, just not in Lemond or Bianchi steel.
One place it exists is in several of the higher-end double butted ti bikes with oversized down tube or at least swagging to create a wider, stiffer area down at the BB. Several manufacturers offer models with specific attention to BB stiffness.
Also check some custom steel manufacturers, like Landshark that can basically build whatever you please characteristic-wise.
|There's a school of thought that BB sway doesn't hurt...||cory|
Jan 30, 2002 12:22 PM
|I don't think I subscribe to it, but there's a theory that in BB sway, the frame acts as a spring, momentarily storing the energy, then releasing it with minimal loss. I get stuck trying to figure out how the side-to-side sway translates to rotational motion of the crank, though.
Seems obvious that you could design a frame to flex vertically for a softer ride but resist horizontal flex across the BB. The susp post sounds like a good idea to me, too. If Performance ever ships the Thudbuster I ordered two months ago for my mountain bike, I'm going to move my cheap Post Moderne to my road bike and we'll see.
|re: is there such thing as||Troyboy|
Jan 30, 2002 12:31 PM
|According to a very well known top end carbon builder, carbon can be made to be every single bit as stiff as you want. Virtually limitless. I don't know that it would then be as light as some ultra stiff alus. It would certainly be a truckload more money.|
|compliant frame withstiff BB?||guido|
Jan 30, 2002 12:42 PM
|Yes. Not only LeMond and Bianchi, but also Colnago, Pinarello, Trek, Schwinn, and many others, even "noodly" titanium (Litespeeds), judging on how those hammerheads always drop me on every hill.
I'm told those aluminum, steel, titanium or carbon fiber frames with compliant carbon forks and seat stays are just what you're looking for. They're all made by high end builders who wouldn't be in business unless they made stiff BBs.
|Try a Softride nm||Mel Erickson|
Jan 30, 2002 1:19 PM
|Thoughts from the recliner||Elefantino|
Jan 30, 2002 2:26 PM
|There are many, but bikes made of steel aren't some of them. Some aluminum bikes, and of course carbon, can be manipulated so that the BB is stiff as a brick.
As for those suspension post suggestions, I second them if you're concerned about BB stiffness translating into the Lambada up your spine. I have an OCLV with a RockShox road post. It adds weight, sure, but darn if the ride isn't wonderful.
I'll probably buy a second RS post for my S-Works when I finally get to ride it, sometime around April.
|Hey man, listen to an expert.||Sintesi at home|
Jan 30, 2002 2:33 PM
|Cycling Know-it-all Sheldon Brown says:
"Stiffness and ride quality
Frame stiffness (or the lack of it) doesn't have as much effect on ride quality as many people would lead you to believe. Let's look at it from a couple of different directions:
This is mainly related to the stresses generated by the forces you create from pedaling. Any frame will flex around the bottom bracket a bit in response to pedaling loads. This flex can be felt, and many riders assume that it is consuming (wasting) pedaling effort. Actually, that's not the case, because the metals used in bicycle frames are very efficient springs, and the energy gets returned at the end of the power stroke, so little or nothing is actually lost. While there is no actual loss of efficiency from a "flexy" frame, most cyclists find the sensation unpleasant, and prefer a frame that is fairly stiff in the drive-train area. This is more of a concern for larger, heavier riders, and for those who make a habit of standing up to pedal.
Another area where lateral stiffness can be an issue particularly to the touring cyclist is the rear triangle, when there's a touring load on the rear rack. An frame that is too flexy in this area will feel "whippy" and may be prone to dangerous oscillations at high speeds. Most of this flex is usually in the luggage rack itself, but there can be enough flex in the seat stays to aggravate this condition.
(Since this article deals with frames, the issue at hand is road shock transmitted from the rear tire to the saddle. Ride qualities experienced at the handlebars are to some extent determined by the fork, as well as geometry, and flex in other bolt-on parts, but are un-related to the choice of frame material.)
Much of the commonplace B.S. that is talked about different frame materials relates to imagined differences in vertical stiffness. It will be said that one frame has a comfy ride and absorbs road shocks, while another is alleged to be harsh and make you feel every crack in the pavement. Virtually all of these "differences" are either the imaginary result of the placebo effect, or are caused by something other than the frame material choice.
Bumps are transmitted from the rear tire patch, through the tire, the wheel, the seatstays, the seatpost, the saddle frame, and the saddle top. All these parts deflect to a greater or lesser extent when you hit a bump, but not to an equal extent.
The greatest degree of flex is in the tire, probably the second greatest is the saddle itself. If you have a lot of seatpost sticking out of a small frame, there's noticeable flex in the seatpost. The shock absorbent qualities of good quality wheels are negligible...and now we get to the seat stays. The seat stays (the only part of this system that is actually part of the frame) are loaded in pure, in-line compression. In this direction, they are so stiff, even the lightest and thinnest ones, that they can contribute nothing worth mentioning to shock absorbency.
The only place that frame flex can be reasonably supposed to contribute anything at all to "suspension" is that, if you have a long exposed seatpost that doesn't run too deep into the seat tube, the bottom end of the seatpost may cause the top of the seat tube to bow very slightly. Even this compliance is only a fraction of the flex of the exposed length of the seatpost. "
"The frame feature that does have some effect on road shock at the rump is the design of the rear triangle. This is one of the reasons that touring bikes tend to have long chainstays--it puts the rider forward of the rear wheel. Short chainstays give a harsh ride for the same reason that you bounce more in the back of a bus than in the middle...if you're right on top of the wheel, all of the jolt goes straight up."
I don't get that 1" deflection either. That's alot. Do you weigh a bunch, or do you ride a really large frame? I think this would be hard to see as well. When your chain scrapes the front derailleur it must sound like a garbage compactor. I dunno.
You have to look at the whole shebang when talking flex. It ain't just the frame. It's the wheels, fork, stem, seatpost, cranks, pedals, etc.... It all adds up. If your ride feels flexy swap parts. My experience is this can have tremendous benefits.
|and another expert||gtx|
Jan 30, 2002 5:46 PM
|1" lateral or 1" vertical?||PdxMark|
Jan 30, 2002 3:22 PM
|There seems to be some confusion in the thread whether it's lateral or vertical flex being discussed. Some of the skepticism in the thread might be based on the assumption that you meant 1" vertical deflection - which seems like alot in the frame.... while 1" seems very possible for lateral.
One comment wondered if lateral flex/deflection would be returned by a spring effect into rotational energy... and Sheldon Brown says all that energy is "returned". But it seems that any lateral effort the cyclist puts into the frame is wasted energy - either laterally flexing a flexy frame or just pushing against a laterally stiff frame. The spring in the frame will efficiently return your foot to its starting position, but the muscle exertion used to push laterally against the frame (rather than vertical to the BB to push a pedal) wouldn't seem to turn the cranks.
Sheldon Brown is likely right that the "energy" is returned by the spring effect of the frame, but the direction of return doesn't seem to help crank a pedal...
One thought: maybe a stiff frame, by not flexing, is better at redirecting sub-optimal lateral pedal stroke into a vertical direction...
|However, energy can never be returned with equal energy||The Pickle Matrix|
Jan 30, 2002 6:16 PM
|or else we would have cold fusion reactors powering our communit .... I mean society. Energy is always lost in action-reaction in this newtonian world we live in. So if the bottom bracket can act as a spring it wont return the same amount of force.
Transfer of energy is disipated.
Jan 30, 2002 6:34 PM
|I guess all that stuff about conservation of energy/mass/momentum that they teach in engineering is just a bunch of bunk. You've actually got things reversed - In the Newtonian world every thing is fairly straight forward and ideal. By definition a spring is an energy storage device and the Newtonian world doesn't account for the losses due to friction. Actually the First and Second Laws of Thermodynamics is closer to what you mean and really sums up the basis for why there aren't any perpetual motion machines.|
|I have the same problem too||cyclopathic|
Jan 30, 2002 7:15 PM
|while I certainly agree that dumping losses minimal, I don't buy the assumption that all "stored" energy transforms into movement.
As you say you have human body on one side of equation and if human muscles were "ideal" springs and could store energy who would bother spring driven exercise machines? that fact that spring stays cold doesn't mean you're not getting workout: you body absorbs all wasted energy
|Yes there is.||Dog Breath|
Jan 30, 2002 3:35 PM
|The original edition of the Rossin Ghibli. DeRosa, and Zunow are a couple of others that come to mind.|
|re: is there such thing as||SnowBlind|
Jan 30, 2002 3:50 PM
|My custom frame with Zona tubing has NO flex, yet rides like a dream.
One trick is some vertical compliance with no lateral compliance.
The other is a short 37.5" wheelbase combined with a slightly (1.5") dropped top tube.
Also going with Zona rather than the superlight but harsher ride of Foco or UltraFoco.
How comfy is it? Got rid of the Gel TransAm and replaced it with a stiff Gippiemme Nitro saddle. Still more comfy than the old Bianchi.
Get a good bottom bracket as well. IMHO if you are going campy and want stiff, get the chorus not the record BB.
I will say one thing: the Bianchi Veloce was eaiser to get out the saddle and climb/sprint because of flexablity made rocking the frame easier(plus the 41.5" wheelbase). The new frame takes all input and translates it to steering, so rocking the frame changes the direction. Getting used to that is interesting to say the least. In fact, part of the reason I got rid of the Trans is that the wider saddle gave enuf input to the bike and I cranked to make the back end "waddle".
|Question for Snowblind...||Nessism|
Jan 31, 2002 5:49 AM
|Please explain to me how Foco & UltraFoco tubing can be harsher than Zona? This doesn't make sense to me considering Foco is quite a bit thinner than Zona.|
|Question for Snowblind...||SnowBlind|
Jan 31, 2002 8:54 AM
|Easy, harshness is a perceived function of rigidity, hence the tendency of Aluminum to be harsher than steel and steel harsher than Ti, as a generalization.
Zona: Rm=1000N/mm2, Rs=920N/mm2 Ap5>10%. Stiff.
Foco: Rm= 1250/1450 N/mm Rs= 1100 N/mm Ap5>12%. Stiffer.
Now, some of the harshness I think also comes from the construction. My Brazed/lugged foco steel is much less harsh than the TIG weilded Bianchi Veloce. TIGged frames seem to transmit vibrations better, while Lugged tend to dampen. But that one is just IMHO.
|A little information...||Nessism|
Jan 31, 2002 11:42 AM
I agree with your statement "...harshness is a perceived function of rigidity..."
But rigidty (or stiffness) is not directly related to a materials strength. Stiffness of a material is quantified by the materials Modulus of Elasticity or E. E is the same for all the different alloys of steel. This means that the Nivacrom alloy in Zona and the Theracrom alloy in Foco both have the same stiffness.
In terms of tube stiffness, a 1.25" Zona downtube will be STIFFER than a 1.25" Foco downtube because the Zona tube has more material in the tube (thicker walls and longer butted section). The higher strength of the Thermacrom alloy allows Columbus to make the Foco tubes thinner without risking failure.
The reason your Foco frame is less harsh than the Bianchi Veloce is because the Foco frame has thinner tubes. The lugs have nothing to do with it. If anything, lugs will stiffen up a frame because they reinforce the joints. This difference is neglegable however.
|A little information...||SnowBlind|
Jan 31, 2002 2:04 PM
the custom is Zona, not Foco. We went with Zona over Foco because I am 225-230, and my idea weight is going to be about 195-205.
I really didn't want to get into the Elasticity verse strength because most people don't get it. M.E. is about how it far it will strech before being fatigued, not how stiff it is. Potato chips are ridged, but not elastic. Bread is elastic, but not ridged.
I should have not said "stiff" and "stiffer".
I really should have said that Foco takes more torque to deflect a identical (mass, thickness) tube than if it made of Zona. Therfore, you can make a thinner Foco tube that still requires the same amount of force as a given Zona tube.
That is I should have said "ridged" and "more ridged".
The thinner the tube and more ridged the material, the harsher the ride will seem.
|A little information...||Nessism|
Jan 31, 2002 3:51 PM
"I really didn't want to get into the Elasticity verse strength because most people don't get it."
At the risk of sounding disrespectful, it is you that doesn't get it. You clearly do not understand the engineering principals that you claim to.
Please do yourself and everyone else on this forum a favor and read the info contained in this link. After reading this, feel free to contact me with any questions.
|I didn't mean to start flame war||cyclopathic|
Jan 30, 2002 6:17 PM
|but the test showing lateral swing is pretty simple.
take the bike, put it in lowest gear, set cranks in 3/9 o'clock, lock front brake and then step on the pedal. You'll see what I mean.
Now imagine riding hill, pushing your weight down.
|I didn't mean to start flame war||tr|
Jan 30, 2002 7:04 PM
|Locking the brake changes the boundary conditions of your test, i don't think that is realistic. It wouldn't be the same as riding uphill and off the saddle. You're loading the bike differently by locking the brakes. You're changing the way the bike frame can carry the load.|
|front brake only not rear||cyclopathic|
Jan 30, 2002 7:25 PM
|while the fork flexing is not resembling riding uphill, forces on rear triangle and BB deflection are identical. Frame is too stiff to flex from front to rear
the most accurate example would be a jump from trackstand up steep hill
|front brake only not rear||tr|
Jan 30, 2002 9:55 PM
|I disagree with you, the boundary conditions are different. The forces on the rear and BB deflection can't be the same if the boundary conditions are not the same. Starting at zero velocity i don't think you are simulating going up the hill at speed. But, it's your opinion and that's fine. I think you need to have both wheels at speed to get the right bottom bracket deflection, they flex a lot more (vertically) than the frame. I don't think you can decouple the motions (vertically and horizontally)and get the exact same answer.|
Jan 30, 2002 8:16 PM
|while the wheel is one of the stongest things on a bike the way they were meant to be used they can have a good deal of side to side flex. when you lock up the bike and push on the crank you also flex the wheels not just the frame, one of the local shops has a folded wheel(it was admittedly an older and weaker one) to demonstrate why someone shouldn't follow through with your suggestion. For a real example do this with a set of spinergy spox on the bike, definately see way more flex. Can also get a similar effect if the tires have low pressure. The only real way to test frame flex is on the frame alone. Check out http://www.sheldonbrown.com/rinard/rinard_frametest.html for how to do this properly. Russ|
|well if you wanna get fency about it||cyclopathic|
Jan 31, 2002 6:20 AM
|then you need to take into consideration BB width, crank Q-factor, wheel flex, tire inflation and so forth
Test requires locking up front only, and while you may flex heck out of front wheel and fork this would not have any effect on horizontal BB movement relative to rear wheel axis
Yes to quantify deflection you would need established procedure, you'd like to remove all irrelevant variables like wheels, fork etc.
Still test as I described would give you a pretty good idea of what bike is a noodle and what isn't. My Al frame is a lot stiffer with weaker 20 spoke wheels then Bianchi was with 32 3x Campy.