# Giant 'wobble'...



## foz (Sep 30, 2004)

I realise this topic has been covered before, but I´m looking for more specific answers to those that I´ve found in the discussions so far...
I am thinking of a new frame, and have had the Giant composite in mind for some time. I have seen them close up, but have never ridden one. However, I?ve read in a few reviews and reports of Giant frames that some people seem to have problems with bike wobble/vibration/shimmy/loss of control on fast downhills. Can anyone here relate their experiences of this? What exactly is the problem - rear wheel sliding out? front end vibrations? rear end vibrations?
Has anyone come to any conclusions about what causes this? The only thing I can think of that would cause it is if a larger rider (or rider with long femur) has the saddle set very far back, and this along with the short wheelbase and chainstays of the Giant frames causes the weight of the rider to be further back over the rear axle, lightening the front wheel and causing loss of grip at the front wheel (like pulling a wheelie). 
Does the wobble happen on straight roads? curves? Smooth? Rough surface? How to correct it? (front wheel braking, rear wheel braking, change of position)
Can anyone who has experienced this give me any info. on your height, leg length, saddle height and setback, plus frame size?
As I say, I have never ridden a Giant and don?t know anyone that has and that has had this problem, but I?m interested to know more about it before committing my money to a frame that may or may not give me problems descending.

Thanks very much

Foz


----------



## filtersweep (Feb 4, 2004)

I am an avowed skeptic of the "high speed shimmy" theory that has been reported here and elsewhere (not to echo the crazy contact area/tire pressure thread). I refuse to believe a frame has a "resonant frequency" that causes such shimmy. I attribute any such reports as "rider error" or a rider induced shimmy. You'll find any frame can be "accused" of such performance. 

Take one out and test ride it...


----------



## sbindra (Oct 18, 2004)

filtersweep said:


> I am an avowed skeptic of the "high speed shimmy" theory that has been reported here and elsewhere (not to echo the crazy contact area/tire pressure thread). I refuse to believe a frame has a "resonant frequency" that causes such shimmy. I attribute any such reports as "rider error" or a rider induced shimmy. You'll find any frame can be "accused" of such performance.
> 
> Take one out and test ride it...


People become quite testy on this bulletin board discussing this subject, particularly when someone attributes the shimmy to rider error. As such, I will not comment on whether the shimmy is a frame problem or rider error. I am merely describing MY experience with the bike.

I have a 2004 TCR Composite 2, size XL. I am 6'1"and weigh 198 lbs. Because I am somewhat in between sizes, I use a 100 mm stem instead of the 120 mm stem that comes stock. The reach on the top tube and 120 mm stem was too long so I replaced with a slightly shorter stem. I have about 2,000 miles on the bike.

In MY experience, I have never had a shimmy at high speeds. Having read about the shim problem, I do my best to stay soft in the hands and shoulders on high speed descents.

In terms of your lost of grip comment, while I have never experienced any shim, people have commented that when the shim starts, gripping tight actually excerbates the problem and that staying soft cures it.


----------



## Trevor! (Feb 28, 2004)

I always think of the wobble as being some urban legend.

I am nearly just on a year of serious road time on my TCR Comp 1 and have never experienced the wobble.


----------



## foz (Sep 30, 2004)

thanks for your replies... I´m not suggesting either that it´s rider error, or the frame, wheels or anything else that could be the cause of this. I honestly don´t think that giant would keep making the frame without modifications to cure the 'problem' if it really was a problem. It just seems that there are far many more reports and discussions of shimmy with giant frames than with any other make. I think I have experienced shimmy on almost all of the bikes I have owned (and they have been several, from custom steel, off the shelf alu, titanium mtb etc) at some time or another . The last time it occurred was last summer, descending on my zeus (orbea) airplane at about 75kph. The front end suddenly lost it completely, and at first i thought it was a front wheel blowout (the sensation was the same, but there was no bang, and when i got it under control it was obvious that there was still air in the tyre. I think what caused it was hitting a bad section of road at high speed, but then again i´ve hit many sections of bad road surface at all speeds and never had the problem before on that bike.
Also, while I´ve been researching my next frame, I´ve been looking at geometry tables, but have not been able to find one for the giant tcr composites. I´m looking for virtual st length, virtual (horizontal) tt length, chainstay length, headtube length and head and seat tube angles. Does anyone have such info for M and L sizes in giant frames, or know where I can find it on the web? 

thanks

foz


----------



## foz (Sep 30, 2004)

I found the geometry tables on the giant australia page. Strange that they aren´t on the UK page... does anyone know why the composite bikes/frame are only available in all black in the UK but are available in several colour schemes in australia and other countries? Is there any chance of getting a non-uk colour in the uk?

foz


----------



## KATZRKOL (Mar 4, 2004)

*2005 TCR's are Different. .*



foz said:


> Also, while I´ve been researching my next frame, I´ve been looking at geometry tables, but have not been able to find one for the giant tcr composites. I´m looking for virtual st length, virtual (horizontal) tt length, chainstay length, headtube length and head and seat tube angles.
> foz


They lengthend the chainstays. .


----------



## Trek_envy (Jun 15, 2004)

*I've been riding...*

a TCR2 for ~5 years (its a '99), and I must say, the shimmy does exist with my setup.

I'm 6'-4, 200lbs, and I ride a Large. (57.5cm) with a 135mm stem. I think the shimmy comes primarily from the stem length. I only feel the shimmy at 60+ kph. You do get used to it, and as mentioned above, keep it loose, and its fine.

I think its a function of any compact Geometry. If you have to use a really long stem, the steering arm gets longer, and your weight gets shifted closer to the fornt axle. This has got to have an effect. Lets just say, my next frame will be either an XL compact, or Im going back to conventional. If you're an average sized person, you should be fine. Just keep the stem short.


----------



## Notgoodbutslow (Jan 10, 2005)

I've been riding a team frame sized medium for about 5 months, max speed of 51mph downhill. I haven't noticed any shimmy or wobble whatsoever. I would attribute any stories of wobble to too much weight over the front wheel (stem too long or questionable downhill posture) or poor headset adjustment. I only get a little front-end twitchiness on seated climbs.


----------



## Trek_envy (Jun 15, 2004)

*At first....*

I was paranoid about the headset adjustment, so I was forever ttightening it. Last summer, while cleaning out the HS, I noticed that one of the cages had disintegrated in the race, so I replaced the HS with a 1" Threaded Shimano XT HS. There is still a wobble.

I really think its the length of stem. For stability reasons, you never see the handlebars directy over the axle. Just imagine how unstable (bump absorption aside) a bike would be with a 90° Head angle, and 0 rake. Death machine.


----------



## AndrewL (Feb 5, 2003)

*check wheels and frame*

In my experience, speed wobbles are a result of a misaligned frame, or incorrectly positioned wheels. I have experienced speed wobble when my rear wheel was not straight in the rear drop outs, and after an accident with my steel frame involving a roof carrier and a parking garage which tweaked the frame. 

Note that I do not have speed wobble experience on carbon or a giant. (hope to never have).

If one of the wheels is not in the drop outs correctly, or the drop outs are not in a straight line (front to back), the bike will not track properly and will wobble at higher speeds.

Just my input.

Andrew


----------



## Leeroy996 (Jun 1, 2004)

Hi there. I own many bikes, this year my race bike is a Giant TCR Composite. I purchased the bike because it is so available and such good value. Keep in mind my answers are based off my comparison to a Prince SL that I raced last season.
I am 5,11" 150lbs, I ride the medium with a 120 stem. The fit is on the smaller side for me. All of the components are top drawer. I have been racing for 20 years.
I find the front end of the bike very flexy - While riding, I can shake the front end and the flex will not reverbarate back to the seat (just the front end flex's). The front end was so unstable it took me a few weeks to get comfortable taking one hand off the bar. And cross wind gusts seemd to be much worse.
The steering is very quick - It's a great bike for cornering - I can corner with a lot of confidence. I'm looking forward to my first criterium (usually I don't)
I haven't had any hint of a high speed wobble. The stability of the front end is a little unsettleing at first though.
Personally I think it's a combination of quick steering and a flexy front end. I'm sure the 05 models have addressed this. My DeRosa has no such issues, but I can buy a few TCR's for that money.
I'd recommend the frame. I like it a lot, it does most things to high standard. No product is perfect but when you take into account the capital outlay it's outstanding.


----------



## deastin (Jun 24, 2004)

foz said:


> I realise this topic has been covered before, but I´m looking for more specific answers to those that I´ve found in the discussions so far...
> I am thinking of a new frame, and have had the Giant composite in mind for some time. I have seen them close up, but have never ridden one. However, I?ve read in a few reviews and reports of Giant frames that some people seem to have problems with bike wobble/vibration/shimmy/loss of control on fast downhills. Can anyone here relate their experiences of this? What exactly is the problem - rear wheel sliding out? front end vibrations? rear end vibrations?
> Has anyone come to any conclusions about what causes this? The only thing I can think of that would cause it is if a larger rider (or rider with long femur) has the saddle set very far back, and this along with the short wheelbase and chainstays of the Giant frames causes the weight of the rider to be further back over the rear axle, lightening the front wheel and causing loss of grip at the front wheel (like pulling a wheelie).
> Does the wobble happen on straight roads? curves? Smooth? Rough surface? How to correct it? (front wheel braking, rear wheel braking, change of position)
> ...




Like everyone here I ll share my experiance with my bike. I have a Large TCR Comp 2, everything stock minus the stem i now have a 90mm instead of the stock 120mm. I m 6'2 and 130lbs. Yes i m super light helps on the climbs! Anyways i ve only experianced the "shimmy" once. During a training ride decending a STEEP hill going about 45mph when it started. I figured i had too much preasure on the front brake and so i put more weight to the back wheel and let off the front a bit and it went away. I attribute this "problem" to the fact that bike is 1 VERY light, and 2 the agressive geometry. the bike tends to put you more forward thus taking weight away from the rear wheel and in some cases making for an interesting ride. Simply my opinion here i m prolly crazy anyways! good luck and safe riding to all
Deastin


----------



## temoore (Mar 9, 2004)

Medium frame w/ 100 mm stem. I have felt it a couple of times, nothing that stayed for any length. My gut feeling is it may be due to the relatively flexible fork/ front end. When riding over undulating bumps, you can feel the whole thing flex a little, making a very smooth ride. Also, while stopped, if you apply the front brake fully and rock the bike forward / backward like you might to check the headset tension, you can see some flex in the fork. 
Anyway, I think in my case it was aggravated by operator intattention.
Great bike, love the lack of vibration/ shock absorbtion.


----------



## rcnute (Dec 21, 2004)

I too have experienced the shimmy on long hills going over 40 mph. Scares the hell out of me. I'm going to ask the bike shop I bought it from what can be done. Everything else about the bike is great.


----------



## rstel66 (Mar 16, 2004)

I have experienced a severe wobble on my aluminum TCR1 on one occasion going over 45 mph down a hill. I now own a TCR Comp (originally a 2, but the only part left from that is the frame). I took it on it's maiden ride since upgrading to a full carbon fork, carbon bar and Ultegra 10 today. I took it on a great downhill ride which I was impressed on how well it steered and I experienced no "shimmy". I have a Med and I'm using a Syntace F99 120mm stem with my carbon bar. I didn't experience any front end flex while sprinting (I weigh about 185 lbs.). IMHO I really like my 04 frame and the modifications I have done. I would consider buying another, maybe this time get a TCR Advanced.


----------



## tomato (May 16, 2002)

*wobble and newer models?*

In the past few years Giant roadbike frames have become less compact than they once were. In relation to the older models, has anyone noticed a reduced tendency to wobble on the newer models?


----------



## temoore (Mar 9, 2004)

*Bad shimmy!*

As I noted a while ago, I have felt the shimmy from time to time. I feel is is due to flexible front end more than anything. 
The reason I am posting again is I road to work today for the first time since moving. My ride has a 1 mile steep descent. Coming down the hill I felt the first stage of the shimmy (and the only stage I had previously felt). Then the front end started shimmying very violently, all I could do to keep control. Slowing down finally brought it back into control. When I checked maximum speed, it was 49.4 MPH (after pulling over, of course). I pulled over and did a quick inspection to see if the headset had loosened, or the wheel bearing adjustments had loosend or what, found nothing. 
I may look into trying another fork. I may also have the bike looked at professionally (I built it myself). I think riding style can increase the likelihood of it happening. This morning was very scary, and I will keep my speed down on this descent until I get it figured out. Still love the bike. 
Medium frame, 5-10, 100mm, 175lbs.
Note, I did put 3500 miles on the Giant last year, and only the occasional shimmy, never like this one.


----------



## temoore (Mar 9, 2004)

*Shimmy followup*

I found the following when searching. Interesting reading.
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3519

Shimmy � 2003.11

_Could you please tell me what causes a bike to get a side to side wobble as the handlebars at speed? This has happened to me twice now at about 35 to 40mph on two different bikes. Is it something to do with frame geometry, riding position, or the set up? The first time it happened was on an aluminium framed racing bike with alloy forks. The shaking was very violent and did not stop until I had virtually come to a halt. The second time, on a Cannondale CAAD 2 aluminium hybrid with steel forks, it was less violent. Can you please shed any light on this as it has dented my confidence in descending the many hills in Dorset. I am 6ft tall and weigh 12 stone.
Mike Pring � Halstock, Yeovil_

That’s shimmy. It’s a kind of vibration where the frame twists and the front wheel gyrates (wobbles) so as to lean and steer alternately left and right. Like any vibration it has a natural frequency that depends upon characteristics of the vibrating system. The key factors in this case seem to be the torsional stiffness of the frame, steering geometry and distribution of weight on the bike.
Vibrating systems “resonate” (the vibration grows instead of dying away) when they are excited (jiggled) at their natural frequency. This happens to a shimmy-prone bike when wheel rpm and wobbles per minute correspond in some way. At other speeds rotation cancels wobble; but around its critical speed the shimmy extracts energy from the motion of the bike to become increasingly violent.

Like any vibration, shimmy can be damped. The main sources of damping apart from air resistance are the front tyre and the rider’s body. Only last year this magazine reported the serious injury of Clive Oxx, a CTC councillor, when thrown by a violent shimmy witnessed by the group he was leading. I examined the bike. It’s one he’s owned many years, it’s never shimmied before and I found nothing wrong with it. Clive had simply fitted a slimmer, smoother front tyre than ever before and inflated it very hard. Broader, softer tyres provide much more damping.

A firm but relaxed hold on the handlebars also provides sufficient damping to ensure that shimmy does not develop beyond an occasional slight shake, even though the bike may be moving at shimmy speed. Once you have suffered high-speed shimmy however, it is hard to remain relaxed when riding fast, especially on the same bike, down the same hill.

It is almost invariably downhill – where gravity feeds the speed that feeds the shimmy – and a smooth road (Clive’s hill was recently, beautifully resurfaced). For although a surface defect may trigger the shimmy – or a stone, a gust of wind, an involuntary twitch from the rider … a rough surface inhibits its growth by randomly disturbing the front wheel.

Never attempt to fight a high-speed shimmy. It’ll be too rapid for any human response and you may instead make it worse. You need to apply passive damping. This is easily done by gripping the frame between your thighs. Simply resting one leg against the top-tube will damp out most cases of shimmy whilst you gently apply the brakes.

A stiffer frame, more trail (an aspect of steering geometry) and less weight on a bike all seem to increase shimmy frequency and speed. That’s usually a good thing to do: because higher frequencies are easily damped – even the skinniest tyre a narrow tyre may do it – and the higher speed may well be faster than the bike ever goes. A heavier rider however, or heavy luggage on the bike, may bring shimmy frequency/speed down into the troublesome range. But there are many different ways to distribute luggage on a bike with radically different effects. The addition of front low-load front panniers often reduces shimmy to a walking-pace weave that’s slow and easy to steer out of.

Bicycles should be designed so they won’t shimmy under any reasonable circumstances; but that’s simpler to say than to do, especially since we also want our bikes to be lightweight, comfortable and easy to steer – all of which tend to increase this behaviour. Cycle designers have little to go on, for although there is some published research on motorcycle shimmy (“weave” and the alarmingly named “tank slapper”), that does not provide exact predictions even for motorcycles.

So if you’re stuck with a bike that shimmies at an annoying (up to 20mph) or dangerous (about 30mph) rate, the first thing to try is different luggage arrangements. You can’t do anything about frame stiffness or angles, but a bit less fork offset (rake) will increase the trail that keeps the front wheel pointed where it’s going, or maybe one with wider blades (stiffer sideways). If that’s to no avail: it’s always possible the bike won’t shimmy under the sucker you sold it to!

And remember the leg on top-tube life-saver. Any of us might need it one day.
Chris Juden


----------



## Bryn (Jul 9, 2005)

foz said:


> I found the geometry tables on the giant australia page. Strange that they aren´t on the UK page... does anyone know why the composite bikes/frame are only available in all black in the UK but are available in several colour schemes in australia and other countries? Is there any chance of getting a non-uk colour in the uk?
> 
> foz


I dont know if you can get other colours in the UK, but im in Australia and recently bought a Giant TCR. Since then ive discovered that this bike is a complete different setup to the same frame bike sold through the US and UK Giant dealers, still a great bike though.


----------



## SSWE5 (Aug 4, 2004)

5'8", 207lbs, 2004 TCR Composite 2, Aluminum Steerer, Medium Size, Velomax Circuit Wheels, Easton EA70 Stem - 120mm, Bontrager Race Handlebar, Giant Carbon SeatPost, Terry Zero Saddle

Have almost 300 miles on the bike in 3 weeks of ownership.

To date the maximum descent speed attained was 45+mph - bike was solid as a rock, road had decent pavement.

On same ride on another downhill, somewhere between 35 - 40 mph, I had some front end shimmy which was caused by the road type and condition - road was of the tar and stone variety, but so compacted that it was like pavement. However, at least in my area (central NJ) the stones are what appears to be spread over the tar broadcast style, thus when the stones wear down with use, subtle waves reamin on the road surface. It was on this surafce that I experienced the shimmy. Clamping the top tube with my knees helped, but it was once that I was off the road surface onto a concrete bridge and smooth pavement beyond that the shimmy was gone.


----------

