RoadBikeReview.com's Forum Archives - General


Archive Home >> General(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 )


Violent Shaking During High-Speed Descents(112 posts)

Violent Shaking During High-Speed DescentsTricone
Jun 7, 2001 11:03 AM
The front end of my bike starts to shake fairly violently during descents once the speed hits about 35 MPH or so. I have to grip the handlebars tightly, and squeeze the top tube between my thighs to combat the feeling of control loss. It's quite unnerving. The headset has been adjusted a number of times to try to solve this problem, to no avail. The latest incident was having a star nut, which was mistakenly placed, changed to a plunger cone. (Apparently, you must use plunger cones for forks with carbon steerers).

Any other suggestions? Someone suggested having the steerer tube refaced and reinstalling the headset. I should note that I am using about 1.25" of spacer, which may be towards the maximum limit for a carbon steerer. I just hope it doesn't involve swapping-out the fork.

Bike: Litespeed Vortex
Fork: Look HSC carbon/carbon steerer
Headset: King threadless 1"
What kind of tires?J.S.
Jun 7, 2001 11:09 AM
I developed an unnerving shimmy when I installed a set of Spedialized team turbo tires. After reverting back to Michelins it went away.
What kind of tires?Tricone
Jun 7, 2001 11:56 AM
Tires are Vredestein Fortezzas, but this has occurred since I obtained the bike, at which time it had Hutchinsons.
re: Violent Shaking During High-Speed DescentsCima Coppi
Jun 7, 2001 11:16 AM
Have your frame and fork checked for alignment. Also, have you made certain both wheels are true and round? Another factor could be a bent or improperly adjusted front hub axle.
Wheels....grz mnky
Jun 7, 2001 11:18 AM
Most likely it is wheel related. Could be as simple as the tires as J.S. suggested, but it may be more involved. I've expereinced this several times and it usually comes down to the wheels. Either they're not true and round _or_ they look fine, but the spoke tensions are very uneven. In any event the results are the same and the wheel(s) are not true under load. An easy test is to borrow a set of known good wheels from a friend and do some comparisons. A good LBS should be able to retension and true the wheels, but if the rims are tweaked it will never work out that well. Give thought to having the rims replaced if this turns out to be the case.
Rarely is it the wheel.norton
Jun 7, 2001 11:52 AM
It more likely is the fork. See the posts below that discuss the fork. This would be caused by the wheel only if there was a gross problem with the wheel.
Rarely is it the wheel.grz mnky
Jun 7, 2001 1:22 PM
So maybe you can provide an explanation of the dynamics involved with the fork and only experiencing this around 35 mph? What do you say if it isn't the fork?

Bottom Line: Been there, done that, got the merit badge.
Rarely is it the wheel.Steevo
Jun 7, 2001 1:43 PM
Monkey brain: 35 mph is the resonant frequency of the frame/fork/rider system.

Go learn some physics before you spout off like an engineer.
Rarely is it the wheel.G
Jun 7, 2001 2:49 PM
I'm not an engineer nor a physicist. Enlighten me about this.
bad advice from the grzD'Ohhh!!!
Jun 7, 2001 12:29 PM
haven't you learned anything from this being discussed over and over again? or maybe you haven't gone to sheldon brown's site, to which someone will inevitably refer the original poster
We'll See....grz mnky
Jun 7, 2001 1:27 PM
No, in fact I've never learned anything in my entire life. I make this stuff up from the safety of the cyber vacuum that I live in.

Been to Sheldon Brown's website and have read the whole thing several times, here's the link since you can't be bothered:

http://www.sheldonbrown.com
seeD'Ohhh!!!
Jun 7, 2001 1:33 PM
"occurs with multiple wheelsets"

it's called high speed shimmy, and is more typical with larger frames and has something to do with the oscillation frequencies. try unweighting or altering the weight distribution when it happens... nothing that has already been mentioned will typically help

spank the mkny
Greasy Chimp is wrong!railer
Jun 7, 2001 1:40 PM
He'll fight it. Watch.
seegrz mnky
Jun 7, 2001 1:40 PM
Yeah, I see now that he added that bit of info below.

Spank your own monkey...;-)
Fairly common problem, and can be hard to fixcory
Jun 7, 2001 11:19 AM
That pops up here every couple of months, and there doesn't seem to be a universal fix. Check all the front-end stuff, tires, headset etc. But on my all-time favorite bike (since destroyed in an unrelated crash), I finally had to live with it above about 38 mph, where I don't spend much time anyway.
The immediate treatment is supposed to be to grip the top tube with your thighs, put some weight on the front end (or take it off, if that makes it worse) and for God's sake slow down.
I've heard just the opposite ...seth1
Jun 7, 2001 12:40 PM
if you feel the high-speed-tremors, that you should speed up. Push through the point at which the shimmy starts. The two times this happened to me I nearly dropped 5 lbs into my bike shorts.
could be the forkHank
Jun 7, 2001 11:32 AM
those Look forks are on the noodely side and you are using a lot of spacers. But as the others have mentioned, could be all sorts of things, though. If it were me, I'd try swapping wheels/tires first (borrow another wheelset), but then I'd replace the fork - go with beefier fork (Kestrel, AME or Wound Up with a steel or AL steerer, or even a steel fork by Steelman or IF) and a good, solid stem (I'd say go back to threaded since you're using so many spacers - it's easy to convert King headsets). Good luck.

Oh, and if you want to get really confused, you can read what Jobst has to say on the subject:

http://yarchive.net/bike/shimmy.html
Another great reason to buy aluminum!! Its all about frame flex!railer
Jun 7, 2001 11:49 AM
Have you ever seen this on an aluminum bike? I think not. Maybe a Vitus style frame, but even then, I doubt it.

The shimmy oscillates at a rate that the rider's mass on the saddle
cannot follow, causing the top and down tubes to act as springs that
store the energy that initiates the return swing. The shimmy will
stop if the rider unloads the saddle, because the mass of the rider is
the anchor about which the oscillation operates. Without this anchor
no energy is stored. The fork and wheels may store some energy,
although it appears the frame acts as the principal spring.
um...Hank
Jun 7, 2001 1:07 PM
I have experienced this on a Vitus - and on the Vitus, I attributed it to the noodely fork, also (first generation Vitus - mid 80s). I'd buy an AL FS mtb frame, but I'll pass on AL road frames.
What a load of Crap!grz mnky
Jun 7, 2001 1:30 PM
So what's the natural frequency? I assume you're measuring frame flex in ten thousandths of an inch.
Greasy, its obvious you are a bit bitter today. Maybe you shouldrailer
Jun 7, 2001 1:38 PM
turn off your computer. Everyone says youre wrong. Dont be mad. We've all been wrong before.
BFDgrz mnky
Jun 7, 2001 1:44 PM
So I'm wrong - I'm sooooo sorry. I'll go to my room. Wait a minute I'm already there. Can I go to your room?

The shimmy thing has always been around. You can get it no matter what fork/frame you have from a set of toasted wheels, bad fork, poor frame geometry, poor technique, etc.
If you're going to cut & pasteWayler
Jun 8, 2001 8:39 AM
information from someone else, give them the credit for it. For instance, Jobst Brandt said:

"The shimmy oscillates at a rate that the rider's mass on the saddle
cannot follow, causing the top and down tubes to act as springs that
store the energy that initiates the return swing. The shimmy will
stop if the rider unloads the saddle, because the mass of the rider is
the anchor about which the oscillation operates. Without this anchor
no energy is stored. The fork and wheels may store some energy,
although it appears the frame acts as the principal spring."

Unfortunately, Jobst' explanation was taken out of context and led you down a path where you only saw the frame as the cause of the shimmy and not as the natural response to what is causing the frame to load and relax. Think of the spring again, a spring has to be stressed to work. This is the point you are missing. Some frames will shimmy at relatively low speeds, the frame shimmy is a response to cyclic stresses and loads, the stiffer the frame, the greater its resistance to applied loads and therefor, shimmy. Think of a bicycle tube as a stress skin structure, which due to the thin nature of modern bicycle tubing, they are. The more "skin" you have for a given material (to a point), the greater area the loads can be spread out. With a bicycle tube, the way you increase the strength of the structure is to increase the diameter of the tube and the wall thickness. Stiffness for a given material is increased at the cube of the diameter of the tube and only at the square of the wall thickness so one sees much greater gains in stiffness by increasing the diameter of the tube. So if you have a load of 100 psi on a one square inch area, the load is 100psi, if that load is now over a 2 square inch area, the load realized for 1 sq in is only 50psi. This is an overly simplistic explanation, but it seems necessary.
Didnt know I was writing a school paper. I will include a fullrailer
Jun 8, 2001 9:13 AM
bibliography of all my references here at:

www.railersbibliographyforjune6,2001thread.com

Thanks for sharing your great knowledge on tubing. (who asked for that?????????????????????????????)

So you finally do agree that a stiffer frame wont shimmy. were making progress here GRZ. So if a flexibe big bike hits a sharp bump at 48mph at an angle and it momentarily jars the front wheel to one side just a little, could it perhaps start a shimmy????????????????????????
Why Do You Assume It's Me?grz mnky
Jun 8, 2001 10:58 AM
Why do you keep addressing responses to "GRZ" - as if I wrote it? If you paid attention to the forum pact at the top you'd see that one of the things that many of us agreed to was to post under a consistent name. If you had followed this forum for any lenght of time you'd realize that there have only been a couple exceptions to my following this. I won't say never, b/c it isn't true.

What you're hearing is the same sort of message from a variety of posters yet you attribute it to all one person. Maybe it's easier for you to think that there is only one protagonist?

It's also naive to think that a dynamic system can be best controlled by looking at one single aspect. Fact is you have to look at the mass, dampening, spring, and driving force to fully understand the response.
Hey grz. I think you are above wallowing in this mud (nm)Len J
Jun 8, 2001 11:00 AM
Oh I dont know, you disappeared, he suddenly appeared withrailer
Jun 8, 2001 11:15 AM
the exact same style, same ideas, fake email address, same irrelevant calulations, and you have a history of doing this. Trust is earned.
more of the same, etc.Breck
Jun 7, 2001 12:23 PM
In order would check...

Headset for play:
Straddle the bike with front brakes locked and firmly rock front end back and forth. Check for play or looseness; should be none. Also with the bike wheel elevated see if the bar/stem moves from side to side on it's own with out any binding.

Hub axle play:
Hold the bar/stem firmly, grab the top of the wheel and push wheel back and forth. There should be little if no play.

Tires for uniformity of rotation:
Spin the wheel and see if the tire spins true and no excess wobble, etc. Take a sight bead on some stationary reference point for this. Also notice if the rim evenly spins in the same plane with the same space from the brake pad.

Fork:
My alum fork on my No.2 bike, a Specialized Allez pro db steel frame would allow the wheel to rub the brake pad on hard cornering! This bike felt a bit flimsy to begin with for mountain fast down hill curves. No fix for this if the fork is not stiff enuff for your riding other than change out the fork.

Wheel spoke tension:
Grab a handful of spokes going around the rim and squeeze firmly.
Tension should feel even.

other as posters said, etc.

cheers and let us know
re: Violent Shaking During High-Speed DescentsTricone
Jun 7, 2001 12:45 PM
Forgive me for not mentioning this previously, but the "shimmying" occurs with multiple wheelsets, and thus, I would tend to rule out the wheels as a causative factor. I tend to believe that the Look HSC fork's carbon steerer has something to do with it. I do recall noting that various pro teams used this exact fork (albeit with less spacer) in the Tour de France some years back, but that doesn't really mean anything, I suppose.
re: Violent Shaking During High-Speed DescentsHank
Jun 7, 2001 1:11 PM
well, those guys are paid to ride those forks, and as you mentioned, you don't see pros with many spacers (and most of those guys are 5' 8" and weigh 140). How much do you weigh and what size frame? Jobst notwithstanding, I'll stick with the fork theory.
re: Violent Shaking During High-Speed DescentsTricone
Jun 7, 2001 1:13 PM
I'm 5' 7" and 135 lbs. But I'm no pro! ;)
re: Violent Shaking During High-Speed DescentsHank
Jun 7, 2001 1:19 PM
interesting. Well, you could try a different stem with more rise that would let you run fewer spacers. Or see if the shop you bought the bike from will let you out on a fork they have lying around - people are always upgrading forks and shops often have used forks - especially steel forks - lying around. This assumes you have a good relationship with them....
There Goes My Theory....grz mnky
Jun 7, 2001 1:39 PM
Well, I staked it all on the wheels since I've seen it so many times. No doubt the excitation force is coming from the dynamics of the wheels. Safe to say you wouldn't have this problem if the bike were moving 35 mph and the wheels were NOT truning (not that this is practical - it just makes the point).

The Look HSC is one of, if not the lightest forks, which means that there's less material than what every other manufacturer thinks you should use. Appears that you're close to the natural frequency of the dynamic system and that the dampening is inadequate. Reynolds touts their Vibration Minimization System - FWIW mine is rock steady up to 50 mph (as fast as I've gone on it).
THe VMS is not for torsional vibrations........ DUH. Its forrailer
Jun 7, 2001 1:43 PM
vertical. Come n greasy. Youve done better. Yes, if the wheels if were not spinning there would be no gyroscopic force for the frequency to fight against. Youve missed the cause.
Why Don't you explain it.....grz mnky
Jun 7, 2001 1:48 PM
So how exactly does this "gyroscopic force for the frequency to fight against" thingy work? You seem to have the answers....
Pick up your front end, spin the wheel as fast as your hairyrailer
Jun 7, 2001 1:55 PM
long arms can muster. Now, as it rotates, feel the gyroscopic effect. Now, imagine going 45 mph, this effect is even greater, plus you have two wheels doing the same thing. The frame is starting to get harmonic waves from the seat tube to the head tube via the top and down tube. Every time it pushes one way the gyro effect pushes back against it, so then it swings to the other side and it repeats itself. Hence the shimmy.
Pick up your front end, spin the wheel as fast as your hairyLen J
Jun 7, 2001 1:59 PM
Why doesn't it happen on all bikes?
What do you do about it?
I ride aluminum most of the time. And if Im on my Ti frame,railer
Jun 7, 2001 2:05 PM
Im not really worried about it because my frame size is only 54-55 so this isnt big enough to be a flexy flyer.

I have seen this on lots of big steel bikes. Small tube diameters and long lengths are inherently flexy. Shorter & fatter ones are not.
I ride aluminum most of the time. And if Im on my Ti frame,Hank
Jun 7, 2001 2:10 PM
well, you may not get any shimmy with that AL frame, but do your teeth chatter over rough pavement? :)

Just screwing around. Glad to see an animated thread. But I don't think this has much to do with frame materials.
Youre right, if you built a 54 steel frame with the same tubingrailer
Jun 7, 2001 2:32 PM
diameters as my aluminum frame it wouldnt shimmy. It would weigh a ton though. Probably 6-7 lbs. Thats the beauty of aluminum, its light and torsionally stiff. What a combo.

Regarding the teeth chattering. I try and try to feel a difference. The ti does feel a bit smoother. But it sure does slither (flex) like a snake when standing in the big ring up a hill. Ive felt a Zurich that feels harsher than my aluminum. Who knows. It could have been my old worn out, thin chamois that day or the tires maybe had 135psi in them. Or maybe it had 36 14 guage spokes. There are too many variables.
agree, except...Hank
Jun 7, 2001 2:42 PM
I think it depends mostly on the builder - not the materials. So I was kidding about the teeth chattering thing (but have you ever ridden a mid 80s Klein - yow). It mostly comes down to tires and proper fit, I think. Wheels (choice of spokes, rims, lacing patterns) don't have any effect on ride quality, though.
Heres a good research study that when read in its entiretyrailer
Jun 7, 2001 2:51 PM
can give one a good understanding of the different frame materials and their affect on ride and strength.

http://sheldonbrown.com/rinard/EFBe/frame_fatigue_test.htm
You think that report gives one a goodWailer
Jun 7, 2001 4:20 PM
understanding of frame materials? Did you read it, and if so, what concrete information did you derive from it? As a study on frame materials under dynamic stresses, that test is so flawed it's not even funny.
How is it flawed? Did your bike do bad?railer
Jun 7, 2001 4:35 PM
Sure, it wasnt a real rider testing the frames but that wouldnt be possible would it? What would be your idea of an unflawed test? Are you related to Grz Monkey?
How is it flawed? Did your bike do bad?Hank
Jun 7, 2001 5:18 PM
I've seen tons of steel Italian bikes break cause of overheating like the De Rosa. I'd like to see how a Richard Sachs would perform on their test (or Steelman or Ibis). And I've probably seen more broken OCLVs than any other bike. And don't get me started on C'dale. So what does that test prove? If it makes you feel better about your bike, I'm happy for you.
It doesnt prove anything but thisrailer
Jun 7, 2001 5:26 PM
It proves that even the dreaded Cannondale can surprise us. Lighter, stiffer, and stronger, and longer lasting. Maybe a bit harsher... I'd like to see a test on that.
have you seen this?Hank
Jun 7, 2001 5:42 PM
I'll be curious to see how this works out, and if others start copying them.

http://www.ibiscycles.com/products/bikes/mtb/ripley/
Again, did you understand what you read?Wailer
Jun 7, 2001 5:23 PM
This will be a shocker to you, I am sure, but just because you read it on the internet, does not make a thing true. Stop to consider the variables of this test which you automatically interpreted as an exhaustive study of frame materials. Were the frames the same size? How many frames of each material were tested? Was there sufficient depth to the data to provide a test that was statistically relevant? Were the applied loads realistic? Were the bikes built to withstand those loads? Was the test biased to favor frames with a specific design criteria? Were the frame design criteria even considered? These are all relevent to the outcome of destructive testing and if you cannot see this plainly for what it is, you're not skilled enough to comment on the validity of said test. Again, stick to what you know well, like your hand.
I told you they just hate it. It cracks me up!!!!!!!!!!!!!railer
Jun 7, 2001 5:29 PM
No, I dont think any of those frames were designed to take blows at the rear dropouts. My bad.

Hows that Ti Serrotta? Watch for cracks!
Wrong again, little man.Wailer
Jun 7, 2001 6:06 PM
Actually, I ride a Wilier, which happens to be made of aluminum. Easton's Scandium alloy to be precise. Nonetheless, I wouldn't expect it to pass that test as it was designed and built for light weight with a measure of flexibility.

By the way, the excessive use of exclamation points is usually a manner of overcompensating for other "shortcomings," shall we say. Nothing you can do about that now, but you would be well served to try to make your personal issues less obvious.
you can fantasize about myRialer
Jun 7, 2001 11:24 PM
crotch all you want. Is that why you got into cycling? Lots of men in lycra??????????????
wishful thinking?Wailer
Jun 8, 2001 9:16 AM
who said anything about your crotch?
People that payed big $ for a supposedly superior framerailer
Jun 7, 2001 4:43 PM
really hate reading this test. It cracks me up.
do you have a clue as to what you are talking about?wailer
Jun 7, 2001 4:44 PM
if the frame was made of steel or ti, it would not need those tube diameters or wall thicknesses to be equally stiff. Both ti and steel are considerably stronger than aluminum and have a higher modulus of elasticity.

"The beauty of aluminum" is not that it is torsionally stiff, it is not, it is inherently a more flexible material than ti and steel. Its beauty is that its low density allows one to use larger diameters to overcome its flexible nature without paying a weight penalty. Do your homework before you start spouting off, professor.
UHHHHHH ok........ Did I ever say different??railer
Jun 7, 2001 5:08 PM
My point was, try to comprehend, is that aluminum can be light (sub 3 lbs) and stiff at the same time. The keyword here is "and". Steel or Ti cannot. If you want a steel frame that is as stiff as a Klein it would weigh 7 lbs. Ti would come in a little lighter. We all know aluminum is softer/flexier tube for tube. But its WAAAAAAY lighter. So just fatten up the tubes and problem solved. Whats the matter GRZ, why don't you use your name anymore??
Ahhhh, that wasn't me.grz mnky
Jun 7, 2001 6:02 PM
False assumption - I've only posted as myslef.

I try to always use GRZ MNKY, unless we're fooling around with flame baiting.

Isn't it time to get back to mtbr.com?
You are amazingWailer
Jun 8, 2001 9:07 AM
you need to engage your brain before you let your finger start typing. Aluminum is on-half to on-third as strong as ti or steel depending on the alloys in question. It also has about 1/2 to 1/3 the mass. The difference is what give aluminum its weight advantage. To make an aluminum tube as stiff as a steel or ti tube, it has to be either a larger diameter or a much thicker wall. To achieve a light weight, the larger diameter with a thinner wall is the proper choice. So to use your reference, if one wanted a frame as stiff as your Klein but out of steel or ti, instead of a 3-pound frame, you'd have 3.2 pound ti frame or a 3.5 steel frame. Could you build frames from ti or steel that equal the super lightweight aluminum frame available today? Yes, theoretically you could, but there are other problems that arise, such as crippling and production issues in working with very thin yet very hard materials. However, there are many sub three pound ti frames that are stiff and don't shimmy, there are also a few sub three pound steel frames now that are the same.
You are amazing!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!railer
Jun 8, 2001 9:20 AM
Please reread the test I posted earlier then rewrite your post. I think it might change.

BTW,why do state such obvious facts like "Aluminum is on-half to on-third as strong as ti or steel depending on the alloys in question. It also has about 1/2 to 1/3 the mass. The difference is what give aluminum its weight advantage. To make an aluminum tube as stiff as a steel or ti tube, it has to be either a larger diameter or a much thicker wall. To achieve a light weight, the larger diameter with a thinner wall is the proper choice. "?

This part needs some checking:

So to use your reference, if one wanted a frame as stiff as your Klein but out of steel or ti, instead of a 3-pound frame, you'd have 3.2 pound ti frame or a 3.5 steel frame. Could you build frames from ti or steel that equal the super lightweight aluminum frame available today? Yes, theoretically you could, but there are other problems that arise, such as crippling and production issues in working with very thin yet very hard materials. However, there are many sub three pound ti frames that are stiff and don't shimmy, there are also a few sub three pound steel frames now that are the same.

Sorry, Ive ridden 4.5lb steel frames that are noodles.
Why?Wailer
Jun 8, 2001 9:52 AM
Why the obvious? Because, Homer, with your ingorant blatherings, you continually disregard it. Twice now you have said that to make a ti or steel frame as stiff as your Klein, it would weigh seven pounds. You also continually reference aluminum frames as being the answer to shimmy problems, which they are not. Many times you have stated that the problem is one of frame flexibility, which it is not. You then go on to say its the nature of ti to be flexy, and contradict yourself that using your own ti frame as an example citing its not a problem for you as your frame is a 54/55, yet the gent with the problem is riding a 51 Vortex which happens to be one of the stiffest ti frames made. I think you have chronic cranial rectitus. I am also sure that you have ridden more than your share of noodles.

Back to the subject at hand, you seem to have again missed the point that tube stiffness is principly derived from tube diameter. A steel frame with a 1-1/8 inch downtube, can be both flexible and heavy due to the small diameter and the thick wall. Same goes for a ti bike with an 1-3/8 downtube. If you build a steel bike out of modern materials, you can have a 1-3/8 or 1-1/2 inch downtube at a very lightweight. Moser, Pinnerello, and others make steel frames that weigh 3 pounds or less in a 55 using oversized (relative to classic steel bike construction) thin wall tubing that are not noodles. Many manufacturers make ti frames under three pounds that are more than adequately stiff. You seem to think flexibility is a bad thing and I agree it can be if you have too much of it. No flexibility however is also a bad thing.

Am I grease monkey? No, I don't know him. Do I hate aluminum bikes? No, I ride one and I like it fine thank you very much. Is there a point to all this? Yes. You attacked others, proclaiming them to be idiots when your own posts testify that you are nowhere near the smartest peanut in the turd, in fact you are consistently wrong. I think you needed a taste of your own medicine. Do unto others and all that. Now be a good boy and quit trying to defend your honor, you have none.
YOure cracking me up!!!!!!!!!!!railer
Jun 8, 2001 11:09 AM
Please call with any questions. Your obvious statements are never befitting of the discussion.

Did you also know that forged aluminum is much stronger than cast aluminum. It aligns the grains in such a manner that it becomes much stronger. And further, if this piece is 1.5mm in thickness it will be weaker than one which is 10mm thick. If this same piece was made out of steel it would be heavier.

Furthermore, please show me your backup (since youre so adamant about this) that shows these 3lb steel frames are as stiff as a 3lb aluminum frame. Also, who's to say what is adequate stiffness. Please put a figure with this before you continue. This way our conversation can actually get somewhere. Thanks.

Question for you, what piece of material is heavier?

a 1" OD Dedacciai steel tube (whatever thier top of the line is) with 1mm wall thickness and 1' long, or.....a 1" OD piece of old Tange number 1 with all the same dimensions.

Whats your pick?
Grz, can you log off & get wailer, he's got a question to answerrailer
Jun 8, 2001 11:36 AM
here. THanks.
One track mindWailer
Jun 8, 2001 12:25 PM
Your stage name is a good fit for you.

I see by your statements above that you are really stressing your mental capacity.

You want proof that a 3 pound steel frame can be as stiff as a 3 pound aluminum frame? Do you understand mechanical properties of materials? Are you capable of calculating simple stress and strains? Does resilience mean anything to you? Does Hookes Law or Youngs Modulus or E = unit stress/unit deformation = Pl/(Ae) mean anything to you?

How about (R1 squared + R2 squared)/R1 squared * .250 * (Sv squared/G)? Or, (Pi/16) * (D4-d4)/D * Sv

If you can figure that out, then you can answer your own question. Adequate stiffness for a bicycle frame can be simply stated as a value that supports the ability of a bicycle and rider to accelerate and maintain forward motion over a variety of surfaces without negative handling traits or inefficiencies. That is obviously an ambiguous answer, yet each rider makes different demands of their bike and what is proper for one, may not be proper for another.

As far as your tube riddle, the answer is obvious that two materials with the same physical properties will weigh the same. What is not so obvious is that Dedacciai doesn't make a 1" tube any longer. Nor can one find standard size tubing on high performance bicycles unless they choose a custom builder. Even OS tubes are getting rare on steel frames unless one is buying a lugged bike. You seem to be stuck in the past -- another symptom of chronic cranial rectitus.

Based on the number of exclamation points on your last posts, it seems you're getting a little worked up. Please try to remain calm, you will eventually learn how to deal with your ignorance. In the meantime, you should probably stop trying to offer advice to others, they deserve better.

Does the formula
Im not an engineer. I started in that program however, butrailer
Jun 8, 2001 12:53 PM
there were no cool people in my classes. They were mostly like you. Most didnt have social skills. So I changed my major. School then became more fun.
No, I don't recognize your formula. Why don't you explain it to all of us and prove that a 3 lb steel frame could be as stiff as a 3lb alu frame and still be functional. Im really, really curious. This sounds like a great bike. If you can, you could start your own frame building biz huh?

Also, the 1" part doesnt matter. Just a simple question. To make it more simple for you, lets just say the OD jumped to 1 1/4" on both expamples. Is that easier? Whats your answer? Your answer cant have the word "if" in it. Just answer tube a or tube b. Did you find out that they didnt make 1" anymore when you asked someone at Deda for the answer?
Wailer
Jun 8, 2001 2:38 PM
You said, "Im not an engineer. I started in that program however, but there were no cool people in my classes."

And that my friend, says everything about you that we need to know. It's also a common response from people who find out that their brains are not as big as their mouths.
Lets see if your brain can answer my request. Come on smarty.railer
Jun 8, 2001 5:23 PM
Why are you evading the question? Break out the calculator and put on those glasses.
Did you ask a question?Wailer
Jun 8, 2001 8:11 PM
Are you talking about this:

"Also, the 1" part doesnt matter. Just a simple question. To make it more simple for you, lets just say the OD jumped to 1 1/4" on both expamples. Is that easier? Whats your answer? Your answer cant have the word "if" in it. Just answer tube a or tube b. Did you find out that they didnt make 1" anymore when you asked someone at Deda for the answer?"

Well you seem to be asking whether two steel tubes with the same physical properties weigh the same, yes, they do. I'm not surprised you could not figure that out for yourself. Now, assuming you are trying to be sly (don't hurt yourself) and wish to test my knowledge of out of production tubeset trivia, then the Tange 1 would be lighter as it is a butted tube with a .8/.5/.8 butting profile, and as such, would be lighter than a straight gauge tube of the same OD with a 1mm wall. Now my turn to ask a question, what purpose did that silly question serve?
Well, you got one of them. Now explain your formulas andRayler
Jun 8, 2001 10:53 PM
how you would make a 3# steel frame as stiff as its 3# alu counterpart. Thanks in advance.
Give a man a fish and he eats for a day....Wailer
Jun 8, 2001 11:07 PM
but teach a man to fish and he eats for the rest of his life.

You shouldn't of quit the engineering course work. The formulas are there, material sciences are well documented, with a little effort on your part, you might figure it out. After all, there are real world examples already on the market. Ask about and see if anyone thinks a Pin Opera is too flexy or a Moser or a Wilier Ultra Foco, or any other number of modern high performance steel frames.
Just as I thought.railer
Jun 11, 2001 9:34 AM
I didnt think you could do it.

Also, can you prove that these 3 frames you mentioned are as stiff as say... a Cannondale?

Thanks.
I am Jack's complete lack of surprise.Wailer
Jun 11, 2001 10:17 AM
You have kind of a sick desperation in your posts. Take the 8-count.

I'm not your parent, no more free rides for you. If you want to quit wallowing in your ignorance, then you need to get your lazy intellect out and exercise it. Yes, it will hurt you, the pressure may even pop the many pimples on your face.

By the way, why would you want a steel frame as stiff as a Cannondale? These are class bikes, not pump me out the door at 43% profit, they'll buy it because we pay Mario to ride one, pay no attention to the failure rate, we weaseled the warranty words Cannondales. That's almost as silly as your pathetic question about the tubesets, which I still, for the life of me, can't figure out what that had to do with anything.
Just as I thought.railer
Jun 11, 2001 1:01 PM
Have a good one smarty.
Two thoughts in one day? Is that a personal best?Wailer
Jun 11, 2001 5:08 PM
Apology for all monkey implications. Uncalled for. Sorry. nmrailer
Jun 7, 2001 2:02 PM
Try this....grz mnky
Jun 7, 2001 2:49 PM
Well this would be all well and good, but the resultant force from moving the axis of a rotating mass (i.e. gyroscope) is in a plane perpendicular to the plane that the axle is moved. See Euler's equations in any Dynamics text. Most of us learned the "right hand rule" (which doesn't have anything to do with hairy palms......) and how to cross vectors in three dimensions. Try taking a spinning bike wheel in both outstreched arms and "steering" - you immediately notice that one end of the axle wants to go up and the other wants to go down.

So why is it that he gets this high speed shimmy while traveling in a straight line and not just while cornering? Place the bike in a works stand and shift into the highest gears, crank the pedals until the rear wheel is spinning at a rate equivalent to riding 35 mph. Notice the oscillation of the whole bike in the stand.

Contrary to what you've said the torque from a gyroscope doesn't reverse itself unless either the applied force or direction of rotation is reversed. This would be where the rider input enters into the equation. Your statement implies that this would happen on all bikes, all wheels, and to all riders. So why does the original poster have a problem while others do not?

Harmonic waves would come from the wheels rotating and being out of dynamic ballance or round due to either weight or geometry (true and round). 35 mph is approx. 616 inches/sec and assuming a 27" wheel would result in and excitation frequency of 7.26 Hz.

Funny: this leads back to the wheel theroy. It also points out that if the fork is a noodle with a natural frequency matching the excitation from the wheel(s) at a given speed then he's going to have a problem. Ultimately it takes two to tango: The fork needs to be a noodle and the wheels need to provide the excitation. The only other factor is the dampening provided by the rider. Just as with any mass-spring-damper dynamic system. Sometimes loosening the grip on the bars stops the shimmy.
No need for me to check your calcs. They're irrelevant.railer
Jun 7, 2001 3:17 PM
Sure, you spin your wheel and there are gonna be some vibrations. They are not perfectly balanced. WHat does this have to do with a frame shimmy??

Shimmys dont happen in corners. Only on high speed straights. Maybe they could happen on a very slight turn.

I never said the gyro effect would reverse, I said the direction of the vibration will reverse and then because this reversing takes place over and over it becomes a shimmy.

I ride a HSC 1. It only weighs 330 grams cut. Ive never experienced speed wobbles on it. Your other points I dont know how to respond. I dont know what the intended point was.
Not if you're using logic.grz mnky
Jun 7, 2001 6:11 PM
Could you do the calculations? My point was you have the potential for an excitation frequency of approx. 7.25 Hz from unballanced wheels on a dynamic system. Don't you think it's just a little coincidental that the problem is a high speed shimmy?

So why is it that the original poster has such problems with a high speed shimmy/wobble/whatever and yet many of us don't? Why is it that so many of the "explanations" point to universal technical urban legends and yet there is no accounting for why some of us experience it and some don't? What makes his situtation unique?

If you ride around at higher speeds with a loose headset and wheel bearings, have a white knuckle grip then yeah, you're going to have problems, maybe this is nature's way of telling you to slow down.
There Goes My Theory....MJJ
Jun 7, 2001 2:29 PM
" Safe to say you wouldn't have this problem if the bike were moving 35 mph and the wheels were NOT truning "
What the heck does "truning" mean???
There Goes My Theory....grz mnky
Jun 7, 2001 2:57 PM
You an editor? Most dopes would figure that I transposed the letters "u" and "r" and meant "turning" as in rotating, but then.....

A decent spell checker would be a nice feature to this website.
do you have a larger sized frame?ColnagoFE
Jun 7, 2001 1:14 PM
flexy fork and flexy frame might be contributing. what's your wheelset?
1.25"??ColnagoFE
Jun 7, 2001 1:17 PM
that sounds like WAY too much spacer for a carbon steerer. What does Look recommend as MAX? I'd say .5" or less would be best or get a rise stem.
That is too much, 3/4" is max., but thats not the cause of thisrailer
Jun 7, 2001 1:35 PM
problem. Nor is it the fork. Its the frame. Its not a design flaw. Its just the nature of the material. Its springy. This happens. Aluminum would be far less likely to spring like this.
Why wouldn't this effect be happeningseth1
Jun 7, 2001 2:46 PM
in the pro races. I assume that they get going a hell of a lot faster than we do. But you don't hear anybody talking about it.
You have now removed all doubt,Wailer
Jun 7, 2001 5:05 PM
that you, Sir, are an idiot.

If your earlier message you stated:
railer Jun-07-01, 01:05 PM   
I ride aluminum most of the time. And if Im on my Ti frame,
Im not really worried about it because my frame size is only 54-55 so this isnt big enough to be a flexy flyer...."

Now you are saying that the shimmy is a result of the frame material being too "springy" as you put it. The gentleman is riding a 51cm Litespeed Vortex, which happens to be ti and also happens to be a fairly stiff frame, i.e., oversized tubes, short spans and moments. How is it that shimmy is not a problem on your 54 Ti frame because it is so small, yet it is a problem for his 51 ti frame?

With your abundant wisdom, please explain how an aluminum frame is less likely to experience shimmy and also why all ti or steel frames don't shimmy at speed. Comparatively speaking, grz monkey is an ocean of wisdom compared to your cess pool of ignorance.

To answer the gents question, it probably is not the frame unless is it significantly out of alignment (it is even possible that it is perfectly aligned which some believe to contribute to shimmy due to a lack of bias to load the frame), it is more likely to be the headset or the CF steerer. The advent of 1" CF steerers has made this a more common problem which was subsequently addressed with the 1.125" CF steerers that are now the norm.
Come on Grz, use your real name. Are you embarrassed?railer
Jun 7, 2001 5:17 PM
I never said my 55 couldnt get speed wobbles, I said I dont worry about it. It hasnt happened. Maybe his is a thinner wall tubing. A smaller frame can take a drastic reduction in diameter and thickness. Maybe Litespeed went too thin. Who knows.

What was your point again GRZ, I mean wailer?
Come on Grz, use your real name. Are you embarrassed?fuzzybunnies
Jun 7, 2001 11:18 PM
why do you automatically assume it could be due to a larger frame. I rather enjoy exceeding 50mph on my size 58cm frame and the only time I've ever had a shimmy was when I hit a pot hole while excelerating past 45 mph on a decent(the rush lasted an hour). I have to agree with grz that the wheels can play a good part though not in this case since it's been stated that it's occured with several different wheel sets. He is right if you set a bike in a stand, spin the rear up to 35 and watch the stand shake like mad, course it is lacking the extra hundred pounds to hold it steady. It's also not to impractical considering car wheels also need to be balanced or steering can be thrown off. In this case since wheels have been ruled out I'd probably toss on a different fork and send the bike up to top speed to see if the shimmy is still there. TTFN
Learn One Thing Railergrz mnky
Jun 8, 2001 11:08 AM
Grz Mnky and Wailer are NOT the same people, although we may be flattered or insulted depending on ones point of view.

Just another example of your flawed assumptions and reasoning.

Read the forum pact: if you can't deal with it go back to mtbr.com
Have you ever seen a spring made of aluminum?railer
Jun 7, 2001 5:20 PM
I dont think so. Have you seen one made out of steel or Ti. Yes, thats what they are all made of. Aluminum is not springy by nature. It doesnt have a good memory. It stays where its bent.
see my post above regarding the Ibis Ripley (nm)Hank
Jun 7, 2001 5:44 PM
nm
Perfect example Hank, although you didnt know it.Rayler
Jun 7, 2001 11:14 PM
the aluminum on the Ripley is not the spring medium. It is the pivot. The spring is up on the seat stay.

But, it does show that aluminum can go through movements and hold up, unlike what Grz said about aluminum and fatigue life. Its just not springy. Its very absorbant and deadening.
Some people you just can't reach...Wailer
Jun 7, 2001 5:52 PM
Have you ever heard of fatique. Perhaps I should be more precise: fatique as it applies to materials and their physical and mechanical properties?

Educate yourself, your ingnorance is an embarrassment to your parents.
.....and some, like Railer, aren't worth it.grz mnky
Jun 8, 2001 11:11 AM
Yep, he's just here to stir things up.

Too bad ignorance isn't painful.
Do you often have conversations with yourself?railer
Jun 8, 2001 11:55 AM
Youre the only one getting stirred up.
1.25"??Tricone
Jun 7, 2001 2:48 PM
Yeah, I'm hoping that the excess spacer stack height may be a causative factor. I'll try cutting down the carbon steerer and lowering the stack height. Incidentally, the frame is a 51cm c-t-t. I'm a little guy.
Sounds like you need a new bike (nm)Leroy L
Jun 7, 2001 2:27 PM
FinallyMel Erickson
Jun 7, 2001 2:49 PM
A really good reason to justify a new bike to your spouse/significan other!
you gotta read this threadTHIS IS GREAT!
Jun 7, 2001 4:25 PM
grz mkny makes an arse of himself!
re: Violent Shaking During High-Speed Descentsmackgoo
Jun 7, 2001 6:38 PM
Are you "guys" really a bunch of girls? Man I shouldn't slam women like this, but that was the first thing that came to my mind.
I would think that you need to take the bike to some one who Knows what thier doing and make sure all the questions about head set steerer are answered. Then go through things one at a time. with the help of a professional.
Roller Coaster RidesBreck
Jun 7, 2001 7:33 PM
I love roller coasters especially the old wooden kind, my favorite being the old 1950's wooden Comet at the Texas State Fairgounds, now moved to Penn., ACE(American Coaster Assoc.)tells me. Steel is great and fast too but have seen no Ti or Al though the three kids coaster cars I have are aluminum wrapped with a plywood floor, steel under carriage, etc.

The physics of a roller coaster is well known and taken into account by the designers. If one falls off the track they figure out why. Get into a padded room and go at it. The engineer Vs the builder Vs the maintenance chief. Theories fly; tempers flare; some times a (wooden) chair. Everybody knows each other and harbors his/her theories and makes the appropriate pet sound, even Brian :) Sounds of discontent; sounds of silence; sounds of excitement. Meanwhile back at the turn stiles the rest of us patiently hold our ticket waiting for the ride to resume. We wanna ride you know but want the ride to be safe, especially on the down grades!

The Fun's on the Coaster, Boyz ...for most of us. For the enlightened ones of course the "funs" after the accident, hopefully no one having gotten hurt. That's the Medic's problem of course and the insurers now a days. Brew the coffee, get out the slide rule, er um HP calculator as we have seen here the numbers get pretty decimally trying to access "fault" and prove with no doubt the validity of at least the theory of what's the matter.

A small aside and i bring no armour(er, um armor! :) to the table here, as the rooms are padded and no one truly suffers the real deal irreparable body damage as the Matrix is explained. Exercise or No a bit of respect for your fellow verbal pugilist. It won't change the argument to be other than clever, but with all good humor, in abrading him or her ...and maybe even help the cars/ bikes etc. back onto the track. That's where the rest of us come in :)

Cheers All
Why not try the spacers on top?RedDog#1
Jun 7, 2001 11:41 PM
I don't see any reson why Tricone couldn't try putting the spacers above the stem and give it a test ride. He might beable to locate the prolbem without have to cut the fork or buy an expensive stem just for troubleshooting. I've done this with my mountain bike until I was absolutley sure how high I wanted the bar and have seen others do the same. Granted it was with steel or alum. steer tube.
Re: Why not try the spacers on top?Tricone
Jun 8, 2001 9:19 AM
That is exactly what I'm going to try doing. I'll relocate some or all of the spacers above the stem and see if the problem persists.
Let us Know -- PLEASE! ;-)grz mnky
Jun 8, 2001 11:28 AM
Yeah, we can argue until the cows come home, but theory has to give way to practice.
Am I the only one who doesn't understand.......Len J
Jun 8, 2001 9:24 AM
All of the discussion above. I think I'm reasonably intelligent but I'm lost.

Are you saying that the shimmy is caused by a resonance from a flexible frame? If this were true, wouldn't all frames of the same model shimmy equally? Therefor all Litespeed vortex's of a similar size to Tricone's would shimmy. This is obviously not true or everyone with a vortex would be responding.

So what are we left with?

Please help this mentally challanged individual (Me)!!
I think its a rare situation that a bike can get the speedrailer
Jun 8, 2001 9:35 AM
wobble. First it has to be high speed. Second, the front wheel has to get bumped in just the right way to get the shimmmy started.

How come we dont ever have any aluminum riders with this issue?
CF & ALBreck
Jun 8, 2001 10:21 AM
My road is a CF OCLC TREK older 1"quill TTT Status stem, King HS, Mavic rims, Ultegra hubs, and have hit 61+mph on local short but steep rough down hill mountain road and mebee only limited by the one "makes me nervous" curve.
No 'Shimmy Shimmy Ko Ko Pop, Shimmy Shimmy Shake'...'atall :)

My MTB is a AL KLEIN older 1"quill Syncros stem, King HS, Mavic rims, White hubs ..& no suspension(mebbe when i hit 60:), and can do 48+mph on local mountain rough(!) single track and again limited mebee by the "makes me nervous" mis-placed curves.
Again no Shimmy, Little Jimmy(Dickens[4'-11"]:)

cheers
Problem Is....grz mnky
Jun 8, 2001 11:23 AM
You've got an over caffinated juvinile deliquent, or two, from mtbr.com having a little fun trying to stir up some trouble. They make a bunch of statements that are based on reading a few magazines and hearing myths hanging around bike shops. They then make false assumptions and feeble attempts to extend the logic and back up their point(s) completely unaware of the true nature of mechanical and physical properties. Their sole source of formal education and enlightenment is to endo after too many bong hits.

The problem is to take what they write seriously.
a small stupid thingAlan B
Jun 8, 2001 10:25 AM
Seeing you've got a Lightspeed and are obviously an experienced rider who has had this looked at I probably shouldn't bother posting this . . . but you did remove the reflectors, right? In CA shops can't sell bikes w/o reflectors and on one of mine the reflector weight through the balance out as you described. Removed the reflector and no more problem.
Yupgrz mnky
Jun 8, 2001 11:25 AM
I started out this thread saying the easiest and most obvious problem is related to the wheels, but that was soundly rejected. Then the sh!t storm got going.
Everybody except your buddy Wailer said you wererailer
Jun 8, 2001 11:34 AM
wrong. You are persistent, calculator boy. Go calculate the resonant frequency of DB spokes vs straight guage at 46.2 mph. This will fix the shimmy.
When I see an aluminum frame get the speed wobbles I'llrailer
Jun 8, 2001 11:46 AM
have to agree with you wont I? It has to be a fat tube frame also. No Vitus style bikes.
When I see an aluminum frame get the speed wobbles I'llMarkar
Jun 8, 2001 12:40 PM
Hey, why the continous bashing of Vitus bikes. I ride one and have never experienced any high speed wobble. I get up to 45mph on rough roads regulary and 50mph on occaison. No problem.
Im not bashing Vitus, in fact I like the soft ride for easy daysrailer
Jun 8, 2001 12:56 PM
Im just saying theyre not as stiff. I think they ride nice. I dont think theyre ideal for a crit or sprint, or hard climbing.
Re: a small stupid thingTricone
Jun 11, 2001 11:24 PM
DOH! The reflectors! Just kidding. My bike never came with reflectors because the frame and components were ordered out-of-state. I guess I was ripped off! ;)