Resonance danger
 

Hey guys, have you ever had your bike start to vibrate rhythmically? Normally I’ve seen this when riding without hands, and the handlebars start to shake and can quickly escalate into something dangerous. I think of this as resonance, and was very happy that my carbon road bike doesn’t seem to exhibit it, but after a few trips to the shop it now has developed a resonance.

Can someone who knows what I’m talking about expand on the phenomenon and suggest recourse, other than holding onto the handlebars?

thanks.

Only on a four pannier touring bike that had too much weight in the rear and not enough in the front.

It’s likely a speed wobble

Barry

The times it has happened to me, I was going over 40 MPH. Certainly gets your attention.

On motorcycles its called “death wobble.” I’ve experienced it on both motorcycles and bicycles, and it can be a little hair-raising. There are some things you can do to minimize risk, make sure your headset isn’t loose, the axle bearings aren’t too worn, and balance your front wheel. Wheel balancing is easy. Put your bike in a stand and rotate your front wheel, let it turn freely, and see if the same side always comes to the bottom. Take a bicycle computer magnet, the kind which attaches to a spoke, and put it on a spoke on the opposite end. You can move the magnet up or down the spoke to change its effect on balance. The wheel is in balance when you can spin it, and it stops in any position randomly.

Putting your fingers in your ears should stop the resonance.

Is this the same bike with the tire where the bead has separated from the sidewall?

Why not go to the "shop" but in reverse?

Does it happen when you see the chemtrails?...

In the UK it is also called a “Tank-Slapper” on motorcycles (handlebars slapping the tank). It is not a pleasant thing….

Was this on the bike you said on 4/8/24 "My back tube popped (tire is worn out so not going to try and replace tube) right as I was leaving work, I have to ride 6.5 miles home and then another 6.5 miles back to work before I can realistically fix it. I don’t think I have a narrow enough tire at home. It feels like a bucking bronco but it’s nothing unmanageable if I keep the speed down, luckily it’s just the back tire."?

Every time I read one of your posts, my hope for humanity dwindles.

Yes, it will still happen.
But I’ve heard covering your helmet with aluminum foil can reduce the severity.

Barry

The "<bike> shop" didn't make it happen.

Did you know there are ways of searching for stuff on the intertubes?

https://velo.outsideonline.com/road/...-to-stop-them/

I got that once years ago my my Ritchey, coming down a short but fast non-technical descent. I hit 40 and the bike started wobbling and scared the hell out of me. I think it was the first time I'd gotten over 40 on it. I had only had the "5 Minute Fit". I took it in for a professional fit, where he dropped the bars, raised the saddle and moved it forward, which balanced my weight better, and it never recurred. I always credited the fit for solving the problem, but years later I read that wobble can be more of a random thing.

I think there are any number of factors that can initiate a speed wobble - road surface ruts, loose headset, unbalanced front wheel, etc - however, whether or not this relatively small input propagates/amplifies into a full-scale wobble is due to different factors, like F/R balance, "death-grip" on the bars, frame flex etc - factors that promote system resonance.. Some frames and rider positions are just more prone to wobble, some just aren't, even if they're traveling on the same roads and descending the same hills. Rider setup can be modified, but some frames will always be wobble-prone, IMO.

Too much weight forward of the steering center.

Speed wobbles. 13ollocks describes them well. It is an oscillation caused by a driving force (that can be as simple as road vibration) and a system (Bike, wheels and rider) with a resonance of the same frequency (or harmonic of it). And it can vary from a minor scare to terrifying and high speed crash causing.

The cause is usually a combination of a particular bike and a particular rider. Sometimes simple changes are a permanent fix. Two things a rider should be aware of, one as a frequent cause of the wobbles and the other, usually a quick fix - the death grip on the handlebars; back off! Firm but NOT rigid! And the preventative/quick fix; place your knee on the top tube. That usually has a very large damping effect on the wobble.

I have one bike with the issue. Sadly my best custom that fits and rides like a dream. Recently I did a fast descent that while not absurdly fast, I have had to back off for the wobbles on the past. Tried lifting my butt a little off the seat with my legs a little more tensed, hands firmly in the drops with real weight on them and the bike stayed quiet. Haven't yet gone to the really fast hills trying that but I see that experience as encouraging.

I doubt balancing a bicycle wheel will do anything to prevent speed wobble.

Add shivering to the list. The only time I've experienced speed wobble, descending Montebello Road when it was snowing.

I'll believe that in a heartbeat.

Muscle tremors from other causes (nerve-related or due to exhaustion) are suspect too.

Climbers sometimes suffer from what they call "sewing-machine leg", which is no fun, either.

Yup. And aging. Or, one of the best preventions is confidence. My bike that wobbles - only showed up once early on. On a cold ride with rain. Now, out of my early 50s and into my 70s, it is far worse. I carry warm clothes and stop and put them on for big descents even though I'll be on nice warm level ground in 10 minutes. On my other, non-wobble bikes I dress the compromise between comfort and convenience.

One of my road bikes is particularly susceptible to speed wobbles. I attribute it mostly to the 50mm wheels, as it will only start to pick up a shimmy at speeds above 40mph, with battling winds present. In dead calm conditions, I've confidently had that bike nearly to 60 w/o issue. I've tried changing my contact points when it starts to happen and keep a light touch on the bars, but nothing seems to fix it other than dropping below 40. Oddly enough, my other road bike with different 50mm rims, doesn't have the same issues. I can feel the wind pushing the bike, yet it doesn't develop the shimmy.

A Resonance Cascade occurs when a Negative Mass Crystal is scanned by an Anti-Mass Spectrometer.

Although I will admit that the possibility of a resonance cascade scenario is extremely unlikely, I remain uncomfortable with the...

So... Speed Wobble...
Front Brake or Back Brake?

As I remember on a Motorcycle it was feather the back brake...