Shimmy Shake Rattle and Roll

There has been a lot of talk lately about front wheel shimmy. Again. Online discussions, Calfee's owners' forum and his own theories regarding fork alignment, a recent accident among my clientele, shop discussions, personal experiences and hearsay. A woman died recently after losing control at high speed-witnesses said that her front wheel was shaking violently. Everybody's weighing in, regarding forks, headsets, wheels, tires, air pressure, frames, hand position, wind, etc. It's the same discussion we had last year, and the year before that. One summer it seems we've settled on HEADSETS as the culprit. Next year, TIRES. This year, it seems we're going toward FRAMES or FORKS.

But it's serious business, as any one who has experienced it will attest. What causes it? What enables it?

I submit that front wheel shimmy can be best explained (and perhaps solved) by acoustics. At a particular speed, your front wheel is rotating at a certain RPM. That number is a Frequency, which corresponds to a particular pitch, or musical note. When that frequency matches the resonant frequency of a component (fork, frame, handlebars), that component will resonate sympathetically.  If the component is not damped (by your arms, for example), the resonance will propagate.

A fork on a bicycle is like a tuning fork. It has a fundamental frequency and a series of overtones that are related mathematically to the length of its legs. If you have a fork separated from its frame, hold it by the steerer and give the fork ends a strum with your hand, then hold the end up to your ear. Hear that low pitch? Feel it in your hand? That's the fundamental. Now, (carefully) whack the fork on the edge of your workbench. Hear the higher pitches, the klang? Those are the overtones, which might be out of tune with each other (which is why it's a klang and not a beautiful note-it's a bicycle fork, not a musical instrument). The fundamental pitch is easiest to initiate, and WHEN, not IF, the frequency of your front wheel revolutions matches the frequency of that fundamental, your bike is going to start shaking.  The pitch will resonate, and will grow (propagate) if not damped somehow.  It might be slight or unnoticeable, it might be dramatic, but it will happen. If you have a stiff fork, the frequency will be higher and your shimmy will occur at a higher speed. If you have a flexible fork, or a longer fork (ie: cyclocross), the fundamental frequency will be lower and your shimmy will occur at a lower speed. If you go slower or faster, the shimmy will disappear, or the wheel RPM will induce an overtone frequency and will be felt as vibration, or perhaps a rattle of some sort.

Your wheels are not perfectly balanced. Lift up the front of your bike by the handlebars, and you will notice that the front wheel will turn and settle to a particular spot. The heaviest point of the rim/tire/tube combination settles to the bottom, and will be located at the rim joint (most commonly), or possibly the valve, or where the heaviest part of your tube is, or where your tire liner overlaps itself, or where your sealant has pooled. Remove the wheel from the bike, hold it in front of you by the skewer, and give it a spin with your fingers. Even if you have an ultra-light, high-zoot wheel, it will want to move up and down in space.  It might wobble or cavitate if the heavy spot is on the side (say, a tire boot or computer magnet), or if the wheel is out of dish.  That's the heavy spot you're feeling, and it's also the frequency of rotation. In mechanics, it is known as RPM, but in music it is known as pitch. It's actually making a sound, something like 1 or 2 Hertz, but that's way lower than the threshold of human hearing. Which is why we call it 110 RPM rather than C-sharp.

Automotive mechanics has parallels. If your front wheels are out of balance, at higher speeds your steering wheel will shake. If you have a fouled or broken sparkplug or wire, one cylinder will misfire and the motor will jiggle on its mounts. Bad CV-joint? Big noise, big trouble. It will shake itself to pieces and put you into the ditch. The next time you're under your car, look at the driveshaft-you will probably see little squares of steel welded on here and there, which balance it. When I replaced the u-joints on my old Z, the manual stated that you must mark the position of the knuckles in relation to the shaft, and replace them in exactly the same way. They were balanced.

When you turn your cel phone to "silent," or "buzz," you engage a little out-of-balance motor rather than your ring tone. When you get a call, the motor spins and it shakes so badly that you can feel it in your pocket, and you know that a call is coming in.

There are other resonant frequencies on a bicycle. The distance from the fork end to the handlebar ends, for example. Or the entire distance from the front axle through the frame to the rear axle.  On my old noodle Tommaso, I don't think I get a fork shimmy but I do get a wobble from the frame.  It happens around 15-17mph, so its frequency would have a longer acoustic length, perhaps the distance from my seatpost to the front end somewhere, or it might be the length of the entire fork.  When I sit up I can feel it immediately, and it will damp out if I put my hands on the ends of the handlebars, but it will not damp as quickly if I grab the handlebars near the stem.  Could it be the length of the fork plus handlebars?  The front wheel seems quiet, at higher speeds as well, but the frame is whipping back and forth.  It's quite dramatic and a little wild, actually. I showed a riding buddy once, and he thought I was going down. (I didn't-it looks worse than it actually is). If I go a bit faster, or slower, it doesn't happen.  If I input an interfering frequency by pedaling, it becomes intermittent.  It will wobble, then still, then wobble, then still (this might be a parallel to the beats you can hear when a perfect interval is not tuned well).  If I damp it between my legs, it stops. I recently took pains to balance the front wheel on that bike: we'll see if it helps.

Stealth Bike...NOT!

Vote for one:

Theftproof bike
What are you looking at?
Please-don't-remind-me-of-1989 bike
Gawd-I-can't-believe-I-had-one-of-those bike
I can't feel my legs
I love that bike
Ugliest bike
Awesome bike!
What's in the pink pack?

ps: note the perfectly matched pedals.

His New Fetish

Driving my son to school one morning I saw in my rearview mirror a car approaching fast. A rice-burner, with ground effects, carbon-fiber hood with nostrils, stupid stuff dangling from the rear-view mirror, etc. Like I said, approaching fast. Wanted to get up behind me before the light turned green, I suppose.
When he arrived, I saw the driver was talking on his cel phone. I looked again, and saw he wasn't talking, but rather, smooching, on his cel phone. Looking yet again, out of the corner of my eye, it seemed that he was actually smooching THE cel phone. Not talking, smooching. Rubbing it on his cheek. Fondling his cel phone. Touching it. Kissing it, licking it. Yes, licking it. Making some kind of love TO his CEL PHONE. Nobody on the other end, I swear, I was watching him in my rearview mirror, and there was no talking going on.
I was shocked.
What the hell kind of...?
A member of L. Ron Hoover's First Church of Appliantology? (See Frank Zappa, "Joe's Garage")
My mouth gaped. I unconsciously turned my face full-on toward my mirror and stared, and he evidently noticed the gesture. Down went the phone, up went the act like nothing happened. Cool, suave, studly dude. Race car driver.
Disconnected freak.
The light turned green, I took my time getting through the intersection, just to see what he'd do. Which was: turn left fast and get his embarrassed butt out of there.

Neat Stuff

"I was just riding along and..."
This is a plasti....er, Carbon Fiber handlebar that broke for no apparent reason. No known trauma, no twenty thousand miles, no rough-and-tumble cyclocrossing, and luckily nobody got hurt. Don't think that we are against carbon fiber-plenty of steel and aluminum and titanium parts have broken too, as you can see throughout this blog-just be reminded that you have to watch out for yourself. Inspect your tires often. Don't tolerate worn or ill-adjusted brakes. Investigate creaks and clicks. Be sensitive to sudden changes in your bike's handling qualities or "feel." Get a yearly, professional tuneup.


1986 ZINN
I had a dream about using brass, or bronze, for lugs, and a week later this guy shows up. I've never seen such a thing-this seatstay cap is polished brass. Cool.

Mostly True Tales from the Trenches

Nice customer story number one:

Bubba Dirtbag came in with his bruised drunken woman and said, "I need a tire."
I ask what size.
"26 by one and three-quarters."
What sort of bicycle is it on?
"An old Schwinn."
Do you happen to have any other numbers off the old tire? There is more than one size called that. Does it say one-point-seven-five or one-3-slash-4?
"It's a 26 by one and three-quarters."
The woman is looking vacantly down and off to one side. A little fidgety, too. Is she used to this?
Well, I'll need to see the old tire, or the bicycle, or the wheel so that I can sell you the right size.
"I said, it's a 26 by one and three-quarters."
Yes, and there are at least four different sizes that are called that, and they are not interchangeable. The rims are different, the tires are different, they are NOT INTERCHANGEABLE. (thinking: I'm not going to sell you a tire and then: a. you use two screwdrivers to crank it on, ruining the tire and your rim, or b. it goes on too loose but you're too ignorant to realize it and it blows up in your face. In either case it'll clearly be my fault for not recognizing that you're the world's most gifted bicycle mechanic)
"It's a 26 by ONE and THREE QUARTERS."
Yes, you said that, and you also said that it's from an old Schwinn, which further increases the chances that it's an odd size. Is it a 559? S7? S6? English? One-speed or multi-speed? (thinking: do you even know the difference between three-quarters and point-seven-five, or might it actually say three-eighths, but the sidewall is too crusty to read) I'll have to see the old tire, or the wheel, or the bike to get you the correct size. I'm not going to waste both of our time by selling you the wrong tire.
"It's a 26 by one and three-quarters. Don't you think that I know what I'm talking about? Do you think I'm some kind of moron? (getting a little hot now, starting to talk a little louder) I've been a mechanic for ALL MY LIFE, I can fix cars and motorcycles and lawn mowers and I've been working on bikes since I was a kid, and etc. etc. etc...."
I'm afraid I can't help you, you'll have to go somewhere else. There's another bike shop up on Littleton Boulevard, you can drive there in about ten minutes. Good luck.
I turn and walk away, and as he's leaving he can't slam the door because of the hydraulic closer. The woman keeps her respectful distance.


Nice customer story number two:

I show up an hour early many days in May and June so that I can be prepared to open on time. Today a half-hour before my clearly-posted opening time an SUV (of course) pulls up, and a woman gets out. She walks up to the door, pulls on it a couple times, looks at my hours, looks in the window, probably sees me working in the back room, goes back to her car, gets her cel phone, makes a call, and then stands by her driver's side door, talking, looking at her watch, leaning on one leg and tapping her other foot. Looking in my front window. Perturbed.
At quarter-to, I unlock the door, prop it open, and start to roll out bicycles which I display in the parking lot. I say, "I'll be with you in a few minutes." She's still standing there, tapping her foot, looking at her watch. By ten-to I've got my bikes out, lined up and cabled-up, and I go back inside, locking the front door behind me. I am not open yet.
Tapping foot.
Looking at watch.
Holding cel phone.
Not open yet.
Perturbed.
I don't make her wait all ten minutes-I let her stew until about five-to, then I go put up the "open" sign and go out.
"I need to work early so that I can open on time," I say.
"Well, fine, then," or something like that.
"What can I help you with today?" I ask.
"What can you do about this?" she asks, opening her back door.
There's a beat-up department store bike lying there, two flat tires, dust and cobwebs, etc. "I can tune it up for you, put some thorn-resistant tubes in the tires, clean it up and then you can ride it," I say.
"Can I come back later today for it?" she asks.
I try not to laugh. "Tune-ups are turning around in two weeks right now, this is the busiest time of the year. I'll do a good job for you, but it will take about two weeks."
"Well, what can you do for me now?"
(me, now)
"I can pump up the tires."
"That's it?"
"Ma'am, this bicycle is a wreck, it needs a complete tuneup and no doubt two tubes, maybe a chain and some cables, and I'm not even going to begin it unless I can finish it. I'll fill the tires, so you can know in a day or two whether they need to be replaced, or you may leave it here and pick it up when it's done in two weeks, or make an appointment with a deposit."
"But my son needs it to ride to work."
"I'll fill up the tires if you like."
"Well, can't you do anything more for me now?"
(ME, NOW)
"If you don't want me to inflate the tires, I'll have to be moving on."
"Well, can't you just check the brakes, and the shifters? Or do a Safety Check? When you pump up the tires?"
"No. I'm hestitant to even pump up the tires, and I'm definitely not willing to accept any liability for this bicycle by doing some half-way Safety Check. There is no such thing as a Safety Check. There's no bike that can be made safe with a check. This bike is UNSAFE. It needs a TUNEUP, which will make it safe to ride. I don't want to waste another moment on this, but I'll pump up the tires if you like. What do you want to do?"
"OK," she says, "you can pump up the tires for me now."
(me now)
I take the bike in, fill the tires, load the bike, and it will probably be in the dumpster by the weekend.

Observations of Frenchness

Riding home some time ago I saw a stunning Citroen SM in a car dealer/restorer lot. Had to stop, and just stare for a while, you don't see these all the time. One of those low-slung, long, wide but small, beautiful, spacepod things, gobs of power and speed in a car that was built to driven by princes and artists and diplomats. A car, along with Jaguar E-series, Mercedes 240, '66 Mustang, that I've always wanted, actually fantasized that I could someday own and drive. Not drive a lot, of course, I'd keep my Volvo for actual use, but how can I explain, you either understand or you can't, what it would be like to just pull up a chair in my garage and sit there and stare. That's mine. I got one. It's awesome. It's French, it's different.

Intentionally. The French are different intentionally, I think. Before they make something, they look around, and they ask: What should work the best in this situation? What makes sense? Can we make it simple and effective? How do the English do it? The Italians? Those insolent Americans? Are there international standards? What does ISO have to say about it? JIS? What is accepted practice? What is normal? And when research is concluded, they sit down to figure out how to do something...else.

Something ELSE. While the rest of the world is using 100mm dropouts, they use...99mm. Where everyone else uses a 5mm cap screw, they use a...8mm...hex head. When everyone else uses paint, they use...chrome. Where everyone else uses chrome, they use...aluminum. Bushing? No, ball bearing. External sleeve? No, internal. Aluminum derailleur? No, plastic derailleur. Plastic shift levers. Even plastic brake levers. Isn't that cool? Plastic break levers. They won't break, they'll work fine. And even though Campy, Shimano, Suntour, Sugino, British, Italian, Swiss, BMX, Octalink, ISIS, it seems EVERYONE ELSE uses a 22mm crank extractor thread, they use...23mm. Except Stronglight, who used 23.35, because of course TA was already using 23.

23.35mm. How many Stronglight cranks have been ruined for lack of a 23.35mm extractor?

So many old French bikes have fallen victim to mechanics. Everybody screws up their first French bike, whether it's a Peugeot UO8 or a Singer. It doesn't matter, you have to be hyper-vigilant, as at some point you won't know whether that fastener is a right-hand or left-hand thread, or whether the nut on the other side is floating or welded on, or is there a bushing in there or bearings which will spill out all over the floor? Move slowly, don't adjust yourself into a corner and then have to re-engineer something.

Ever try to mount an old Ideale saddle? Sometimes your clamp tightens, sometimes it won't because the RAILS ARE A SMALLER DIAMETER than everyone else's! You have to use a French seatpost to do it reliably, but of course French seatposts are a special size, which means that you have to use a French frame, and then only French derailleurs, BB, headset, and hub O.L.D. fit into a French frame properly, so you might as well just capitulate and get a French bicycle if you want to use an Ideale saddle.

My (wonderful, sublime, French) randonneur bike has a 26.4mm seatpost, which the seat tube had to be shrunk to accept. And they didn't even do it well, I think perhaps in spite. Just to say, "see, here we thumbed this up just to annoy you, (vous poor uninlitenende anglais tripe), but we still think it will work fine." WHY DO THAT? Is it so important to use 26.4 that you have to alter a carefully-drawn tube to do it? Why not just use the 27.0mm that the tube is designed to take? Is it more convenient to swage a steel tube than it is to turn a different diameter into aluminum? If you have to use that seatpost, then why not use your own frenchy tubes duh that are already made to fit the post already duh, is that too obvious duh? Craziness!

Before WWII, when French gunnery experts were trying to decide on a bore size for the primary guns on battleship Richelieu, they certainly knew that other great maritime powers were using 14-inch, 15-, 16-, 17, and even 18-inch guns (bigger is better, normally, on a battleship). And of course having this information, they had a great and doubtless heated discussion over whether to employ....13.4-inch or 13.8-inch.

Have you ever had a pair of French shoes? I haven't. Italian, sure, I have four or five pairs, great shoes-they fit better the longer you have them. Chinese shoes, of course, a couple of pairs, cheap and effective, disposable, fit well new and wear out fast. English shoes, yes. American boots too, even got some Dutch clogs. But no French shoes. Why is that? Do they have special feet there? Not like Everybody Else's?

Vive la difference.

But that gorgeous car, I don't care if it's different. Maybe that's part of its charm. Think of automatic shift levers in cars...where do you imagine them? Of all the cars you've driven, how does the shifter work? Up and down, right? Whether it's on the column or on the hump, it's UP and DOWN. Or maybe TO and FROM. This one works...from left...to right. Or perhaps right to left, does it matter? Perhaps buttons on the ceiling were not possible? And I don't doubt that it's not the normal P-R-N-D-2-1, either. Probably R-N-1-2-D-P. It only makes sense if you're already used to it.

Open the hood, and what do you expect? Wires, hoses? Sure, lots of 'em. Maybe a nice polished cover? Black plastic cowls and a huge radiator? Ha. Green Hydropneumatic Spheres. That's right, green balls, at least four of them the size of large grapefruit. They operate as parts of the suspension, to raise and lower the car, among other things. What an interesting, great, completely arcane idea...raise and lower the car hydropneumatically. Self-levels with a load. Tiptoe through puddles, hunker down at higher speeds. Float more on cobbles. Bounce up and down at intersections. We can use it for steering too, and the headlights. Use it to adjust the windshield wipers. Maybe it can be hooked up to the radio. It won't leak. Air never leaks, neither does oil...it'll work fine. And how many headlights would you like while we're at it? One on each side? Maybe two on each side? How about six? Six headlights, three on each side, two pivoting with the steering wheel, which automatically re-centers when the car is not in motion.

Also, an oval steering wheel and gauges, aluminum bonnet, stainless trim. Front wheel drive. Carbon-fiber wheels were an option, as was a set of fitted luggage. Maserati engine, Lotus transmission. The brakes are operated with a button on the floor, not a pedal as with lesser cars.


Different.

Evidently the cars imported to the U.S. had four headlights, we just had to put our foot down. Picture used without permission and may be removed for any reason at any time.

Like beef? Pork? Chicken? Rattlesnake? Mule?
Try snails.

Potatoes? Onions? Turnips? Mushrooms?
Truffles.

Eiffel.
Debussy, Ravel.
Impressionism.
de Balzac.
Napoleon.
Cathars.

Well, I'm no expert. Don't even speak French. Never been there. But I sure liked that car.

More of the same

This happened while parking the bike. Really.










This is not the same bike, this is a Rivendell. Very nice USA-produced frameset with hand-carved lugs. Extremely clean workmanship-filing, brazing, prep and paint are all wonderful. Hit this picture with your pointer and get right up close-try to find a flaw. I don't know any other maker that uses points so slim, or three waves on the top-this lug is unique to Rivendell, and won't ever be mistaken for another brand. A little opulent maybe, even baroque, but hell I'd ride it. Get it good and dirty!

5-9-08
I have been informed that this lug was actually supplied by Richard Sachs. It appears also to be used by Ted Wojcik, and perhaps others.