Over on the Serotta Forum the subject of shimmy was being discussed; this subject is probably discussed on bike forums more that any other. One member posted the following:
“Am I nuts, or do all shimmy prone bikes have one thing in common? Large size frames. I ride a 52cm - 53cm frame. I've never experienced shimmy in any of the many bikes I've owned. It seems like every shimmy story has a tall person in the starring role.”
No, you are not nuts, large frames are more prone to shimmy. First of all, shimmy is a natural occurrence on two wheeled vehicles, bicycles and motorcycles have the same problem.
At a certain speed a spinning wheel will start to nutate, That is, not only is the wheel spinning about its axis, (The wheel spindle.) the axis itself is constantly moving. To demonstrate this to yourself, hold a wheel by the spindle in your outstretched hands, and move your hands in the motion of pedaling a miniature bicycle.
Even a child’s spinning top will hold steady with its axis vertical if it is spinning at speed. One would think it would spin slower and slower until it gently falls over. However, as it slows to a certain critical speed it will start to wobble then fall. In other words, it starts to nutate at a certain speed.
“Rotation” means an object spinning around a fixed axis; “nutation” means the axis is also moving as the object spins. The front wheel is not only fluttering back and forth in the vertical plane, but in the horizontal plane also. Therefore, the head tube of the bicycle or motorcycle is shaking violently from side to side.
The rear wheel does not shimmy because it is fixed withing the frame. Just as on three or four wheeled vehicles the wheels are not prone to shimmy because the axels are held in one plane. Although on older cars, for example, when wheel bearings and steering joints start to wear allowing the wheel’s axis to move, they too will shimmy or wobble at a certain speed.
On a bicycle, most of the rider’s weight is towards the rear. The rider’s weight on the saddle and the rear wheel in contact with the road provide two anchor points holding the rear of the bike steady, while the front end can start to shake violently.
Because the seat tube slopes rearwards, as the frame gets taller the rider’s weight is more directly over the rear wheel. On a large frame this makes for a near vertical pivot line between the rider’s weight on the saddle, and the rear wheel’s point of contact. (See picture below.)
It is about this pivot line that the bike will start to shake, and if the rider then grips the handlebars tighter, his body will also start to shake along with the bike and a crash will probably ensue.
When nutation and the resulting shaking starts, it will only get worse unless speed or weight distribution changes; especially if the rider becomes part of the shaking mass.
On a motorcycle shimmy, (Or tank slapper, as they are called.) they are often so violent the rider is thrown from the machine. In this motorcycle tank slapper video, you will notice the front wheel is not just fluttering side to side about the steering axis, but the wheel is also moving side to side about a horizontal axis, throwing the whole bike and rider side to side.
On a smaller bicycle frame, the rider’s weight is more forward and the pivot line is less than vertical. (See picture below.) This means that even if the rider is riding “no hands” there is still a certain amount of weight on the front wheel.
This is a clue to avoiding shimmy if you are tall and ride a large frame. When descending at speed, move your weight forward and keep your back low so that air pressure on your chest is not forcing more weight to the rear.
Transfer weight from the saddle to the pedals, thus breaking one of the solid anchor points. Often a knee pressed against the top tube will dampen a shimmy. A loose headset may not cause a shimmy, but tightening a headset very slightly may have a dampening effect. Don’t over tighten a headset, or this in itself will make the steering erratic.
This is the third time I have written on this subject, and I don’t want to keep repeating myself. However, it is a subject that will always be around and so will continue to be discussed, and continue to surprise those who experience it for the first time.
In my first article “High Speed Shimmy” I called it a design flaw. This may have been a little strong, but frames I built did not shimmy as a rule, even the larger sizes; so, design and construction do play a role. The only time I was told a Fuso shimmied was when rear pannier bags were fitted, and the frame was not designed for this purpose.
I built my frames with slightly more trail than most other bikes; maybe this factor was enough to prevent shimmy. It doesn’t take much to alter a bike’s handling characteristics. Sometimes different wheels or a slightly heavier tire is all that is needed to stop a bike from shimmying.
I went into the subject in depth in my second piece called “Shimmy Re-visited.” I am now of the opinion that this is not so much a flaw, but a natural phenomenon inherent in any two wheel vehicle. Simply because the front wheel’s axis is free to move in any direction.
All the years I built bicycles, I never gave this subject much thought; I didn’t have to because I never had this problem. I do not have an engineering or science degree, and those who do will no doubt correct me if I am wrong.
I have not written about harmonic vibrations and the reasons why wheels start to wobble, what is needed is not more theories as to why this happens, but ideas to minimize the problem.
Bicycle designers and manufacturers should be concerned, and be looking for a cure. In the mean time, all an individual can do is get to know the limitations of their bike, and ride within those limitations.
Over on the Serotta Forum the subject of shimmy was being discussed; this subject is probably discussed on bike forums more that any other. One member posted the following:
In 1982, soon after I started building my own custom frames, I built a 58cm. frame that was somewhat of a showpiece. It was dark blue with lots of chrome.
I am pretty sure this was the frame I posed with in the Masi shop, and was used in one of my early ads. (Left.)
The frame was eventually sold to Bud’s Bike Store, in Claremont, California, and built up as a display model. This bike brought in many other orders, including this one built in 1983.
Then around 1984 this display model was sold, and bought by Lorin Youde. In his own words he told me, “I rode the heck out of it, then for some unknown reason, sold it in 1994.” He added, “Even my wife told me not to sell it, and it was not long after I realized I had made a big mistake.”
Lorin tried to fill the void with other bikes I had also built; he bought this John Howard two years ago.
Then he bought this Recherché in near new condition; it was the one I featured in this post.
Last year Lorin decided to track down the bike he sold. The person he sold it to had resold it, and the bike was in now Spokane, Washington. The new owner had just had knee surgery and so was willing to sell.
A price was negotiated, and the bike returned to it’s original owner at the end of last year. Lorin just sent me pictures. In an email he told me, “I replaced the 8 speed Dura Ace components with period correct Super Record and while not quite in pristine a condition as Chuck Schmidts' it still looks pretty good and is a pleasure to ride.”
Actually, I think the original paint looks pretty darn good for a bike that has “Had the heck ridden out of it.” There are more pictures here.
There is a new hazard for cyclists that has been brought to my attention.
The chances of anyone experiencing this is remote, but never the less it would be remiss of me if I didn’t pass on this information.
It is a strange phenomenon known as Spontaneous Cyclo Combustion. (SCC.) It is similar to Spontaneous Human Combustion (SHC.) but is relatively new.
The first recorded case took place in Southern Italy in 1985, whereas SHC has been around for hundreds of years.
Since the late 1990s there has been a rapid increase in the reported cases, last year (2007.) there were four incidents in the US alone. Two in Arizona, one in Nevada, and one Southern California. SCC seems to be more prevalent in hot, dry climates.
Unlike SHC caused by the melting of body fat known as the "Wicking effect," the cause of SCC is unknown. The end result is the same, the body burns completely, but cyclists have very little body fat, which has scientists somewhat baffled.
Prior to last year, in all known cases, the victims of SCC for some unknown reason, had all been riding alone. In each case the cyclist’s charred remains were found, usually a short distance from their bicycle, as if they had dropped their bike and tried to run from the source of heat before being totally consumed by fire.
However, in one of the Arizona incidents last year there was a witness. Two cyclists, let’s call them Tom and Brad. Tom is deceased; Brad wishes to have his name withheld for reasons that will become apparent. The two were riding in the desert somewhere north of Scottsdale, when Tom the stronger rider dropped Brad on a long climb.
By the top of the hill, Tom was some 300 yards ahead. Brad looked up and saw a bright glow ahead. At first he thought it was a trick of the sun on the hot asphalt, but then he heard cries for help from his friend. By the time Brad reached his friend, his bike lay by the roadside and Tom was fully engulfed in flames some thirty feet away.
Brad grabbed his water bottle and ran to help his friend. However, the heat was so intense he could only get within ten feet of the fire, and in less than a minute all that remained of Tom was a heap of smoldering black ash.
Brad called 911 and while he waited for the police and EMS he took pictures with his cell phone. When the police arrived Brad was promptly arrested on suspicion of murdering his friend. He was held for several days then interviewed by the FBI. After the interview, he was allowed to go home but never told that he was cleared of any wrongdoing. Which is why Brad wishes to remain anonymous.
On arriving home he discovered the pictures he took had been erased from his cell phone. It appears in such cases where some strange phenomenon occurs; our government becomes secretive, and suppresses information.
In the California incident, also last year, it is believed a cyclist who spontaneously combusted accidentally started one of the more serious wild fires that plagued that state. California fire investigators denied it, in what appears to be an official cover up. However, they did say if anyone should catch fire, to resist the urge to run into the surrounding chaparral.
So why the increase in cases of SCC in recent years? Scientists believe it is directly related to carbon fiber frames. It is believed that it is triggered by a build up of static electricity caused by the friction between the plastic saddle, and the polyester fibers in the shorts.
The padding in the shorts is usually highly flammable which adds to the problem, and may even be the primary key in this whole SCC issue. It's like the cyclist is sitting on a fuse to a potential incendiary bomb.
With the old steel frames this static electricity was constantly dispersed throughout the frame. A spokesman for Brooks Saddles in England said, " We have known about this for years, but were afraid to make it public because.......well......we might have appeared a little cuckoo."
He added, "It's the reason we increased the size of the copper rivets in our saddles. (Picture right.) Copper, as you know, is an excellent conductor of electricity and it directs the static electricity away from the danger zone."
So what can a cyclist do to avoid this slight but definite hazard, besides riding a steel frame with a Brooks saddle. Well help is on the way; manufacturers of plastic saddles and shorts are getting together to find which materials do not cause static build up.
It will be necessary to buy the correct shorts to go with a certain saddle. Each will have a warning label, and a code letter. (A, B, or C.) A type “A” saddle must be used with type “A” shorts, and it is not recommended that you mix code letters, or you may be actually be placing yourself at an increased risk.
These new saddles and shorts will not be available probably until early 2009. So what can a concerned cyclist do in the mean time? The incidents are so rare that I am not suggesting cyclists should become paranoid to the extent of carrying a fire extinguisher.
However, there are any number of proprietary flame retardant materials available, that you can use to treat the padding, and make your shorts fire proof. Or, you can simply keep the padding damp throughout your ride with water from your bottle.
There is a website with more information at BlazingSaddles.org
The following comment was made on my last post:
"I agree that we all share the roads, etc. What I do not understand is cyclists who will steadfastly ride in the middle of a thoroughfare lane while cars back up for blocks behind them not being able to pass.
Sure, bikes have as much right as anyone else to be on the street, but what they do not have the right to do is block a lane or impede traffic.
Politeness and common sense dictate that they get out of the way and allow others to pass if they cannot keep up with the flow of traffic."
To many non-cyclists “Share the road” means, “Okay I accept that you have a right to be on the road, but just stay out of my way.” This comes through in the last sentence of the above comment.
Politeness and common sense need to prevail on both sides, otherwise it is not a true “Sharing” of the road. I would be happy to stay out of the way and ride to the extreme right, if in return other road users would have a little concern for my safety and not pass me at 50 or 60 mph, missing me by inches.
Most people drive in the middle of the lane leaving equal space to the edge of the lane on either side. Many will simply hold that line when passing a cyclist, when “Politeness and common sense” would suggest steering to the outside edge of the lane thereby leaving more space on the inside.
If it is a two-lane, divided highway, and there is no one along side or about to overtake, signal and move to the other lane, or at least put the car’s wheels over the line. The same on narrow rural roads, cross that center line if it can be done safely, if not, stay behind for a brief moment, and then pass. A cyclist is less than 7 feet long and 3 feet wide, it is not like passing an eighteen-wheeler.
Many states are bringing in new laws to give cyclists a minimum of 3 feet when passing. If politeness and common sense prevailed, these laws would be unnecessary. So in the mean time, I exercise my right to “take the lane,” in other words move to the center of the lane when it is unsafe to pass.
A good example of this would be where there are cars parked at the side of the road. I will not ride within 5 feet of a parked car because people will fling open car doors without warning. Five feet will usually put me in the middle of the lane, if I ride any closer cars will still continue to pass at their normal speed.
If someone opens a car door I have nowhere to go. I am not only injured by running into the edge of the door, I will most likely fall in the path of a passing car. It is unfortunate that city planners allow parking for long stretches of city roads, without understanding the real danger this imposes on cyclists.
Another situation where I would take the lane is if I want to make a left turn ahead. (Right turn in the UK.) On a multi-lane highway I may need to start the maneuver several blocks before I actually turn.
From the right lane I will wait for a gap in traffic, signal and move to the center of the lane, stopping any further traffic from passing. I cannot safely get into the second lane from the extreme right edge of the first lane.
Then when there is a gap in traffic in the second lane, I signal move over again. Sometimes an impatient driver will also see this gap and try to go around me. If this stops me from changing lanes then all the traffic behind me continues to be delayed because one selfish driver didn’t allow me to get over and move out of the way.
When I reach the left turn lane, I stay in the middle of that lane. If I move to the left of the lane, cars will pass me on the outside and after I complete the turn, I am now stuck in the middle, needing to get back over to the right.
If I move to the right side of the turn lane, now I have traffic passing at speed on both sides. If one should hit me, I would be knocked into the path of another vehicle.
This is often a left turn at a traffic light. Everyone is rushing to make the green light, no one is concerned for my safety except me, so forgive me if I appear a little “selfish” at this point.
More people would commute to work by bicycle but they see it as dangerous. As time goes by, economic reasons will force some to overcome this fear. Every bicycle on the road means one less car; people will become more aware of bicycles and drive slower and with caution. People will actually get to their destination quicker and safer because there will be less congestion.
The picture at the top is Savannah Hwy. (Rt. 17.) the main road south out of Charleston, South Carolina where I live. Traffic is heavy during the week, but moderate at weekends. Not the best place to ride, but necessary to get from where I live to some of the more rural areas on John’s Island, and Wadmalaw Island.
The road has a narrow shoulder and “Share the road” signs are posted. It is a divided highway with two wide traffic lanes in either direction. I ride on the shoulder and in spite of this drivers will pass me within inches at 50 to 60 mph as I described earlier, even though there is no traffic in the outside lane.
I use my “take the lane” right sparingly and only when absolutely necessary. If I delay other road users briefly, I am doing it in the interest of my own safety, not just to piss people off.
After my last article when I expressed my faith in human decency, that faith was put to the test when I read of the aftermath of the Bay Area tragedy when two cyclists were killed by a sheriff’s deputy’s car.
The media reflecting public opinion take on a “Blame the Victim” attitude. Although not in this specific case, but in talking about cycling related accidents in general. Public opinion after a cyclist is killed or injured is often, “He or she asked for it by being on the road.”
This same attitude existed back in the 1940s and 1950s if a woman was sexually assaulted. Public attitude often was, “She asked for it by dressing provocatively.” Police would do little to pursue such a case; in other words blame the victim.
The press and public opinion go hand in hand. The media can influence public opinion, but at the same time, they pander to popular opinion. Newspaper columnists know if they write an anti-cyclist piece it will get the support of the anti-cyclist public, and sell newspapers.
When Matthew Parris wrote in the London Times, advocating decapitation of cyclists with piano wire, there was an outcry from the cycling community, but little support from the general public.
Mr. Parris is not the only one to have written such inflammatory anti-cyclist articles. If these journalists used the words, Black, Jew, or Moslem in the place of “Cyclist” they would have been hauled off to jail.
In the same way that the media panders to public opinion, so too does it influence police attitude. Sheriffs are elected and police chiefs are beholding to elected officials. If police took the same “Blame the victim” attitude towards rape victims as they did 50 or 60 years ago, there would be an outcry from the media and the public.
There would also be public outcry if there was a racially motivated attack on a black man and the police failed to pursue the matter. Yet in Tucson, Arizona police refuse to pursue a case after a cyclist was struck with a baseball bat. Even though the victim provided a license plate number, and the cyclist’s lawyer knows who the assailant is, and where he lives.
In America a person can no longer attack a black or Jewish person, or a gay guy without serious consequences, these are hate crimes. Why is it then a driver consumed with road rage can take a baseball bat to a cyclist and the police look the other way?
Just read any online rant by someone on a blog or forum concerning cyclists, and they inevitably start talking about the skin tight shorts, those ridiculous shoes, and of Lance Armstrong wanna-bes. Totally irrelevant to the original complaint, but showing that all too human trait, to hate those perceived a little different.
Viewed in this light, isn’t the whole issue of people riding bikes on public roads a human rights issue? Cyclists are human, and they have a definite right to be on the road. Yet I have never heard of a cycling advocate pursuing it in this light, or a lawyer arguing that a cyclist’s civil rights were violated.
In the US, it is against the law to discriminate against anyone on the grounds of race, religion, sexual orientation or gender, etc. etc. Maybe mode of transport should be added to that list. Discriminating against, or hating someone because they are riding a bicycle, is just as ludicrous as any other form of discrimination, and has no basis.
I still stand by the sentiments of my last post. Cyclists behaving badly serves no useful purpose, and only provides fuel for the hate mongers. It can increase the danger; if not to you then to other cyclists. People on the roads are already insane; you would hardly give the finger to someone coming at you with a baseball bat, so don’t do to the guy in a three ton SUV.
That doesn’t mean we keep taking this crap and do nothing. We keep making our presence known, and people will realize we are not going away; in fact our ranks will swell.
To draw a parallel with the human or civil rights movement of the 1960s, people achieved what they did by protesting in a peaceful manner, even though violence was used against them.
I will keep writing about the issue whenever it arises, and I am hoping others will pick it up and run with it. As I have said before, in time the message will reach the mainstream media.
Now, if I could only make the case that cycling is my religion……hmm.