mustang1

bike: Specialized Allez, alex DA16 rims, first on Specialized Mondo tires (120psi) then on Michelin Krylion (116psi).

This is the 2nd time I've had what I can only describe as severe shaking. I'm doing about 30mph, slight downhill, the road surface turns a little rough (nothing too bad though, just not smooth). My bike started a gentle wobble which I thought was just the road surface (makes sesnse) which then turned into a big wobble where I thought the wheels had come loose from the frame. So I applied the rear brake bringing my self to a stop but before I could, the bike pretty much went into a violent shake, like a pendulum, there's no way I could have controlled that at 30 mph and I would have gone down. So applied front brake, hard, stopped, got the bike off the (busy) road.

Didn't find anything wrong with the wheels, tires, spokes, nuts attaching the wheel to frame were fine. This shaking also happened during a right hand turn, at about 15mph: again, severe shaking to the point where I had to abandon the turn (mid way) and slow down, going straight for the sidewalk but I stopped in time.

In both cases, the weather was dry, road surface a little rough (but nothing out of the ordinary), slight downhill. My bike has an aluminum frame with carbon forks and seatpost. Both times I was not pedalling (just coasting).

What caused this?

Deanster04

You have the dreaded speed wobble. Could be a loose headset or an alignment problem. Have it checked out.
The only safe way to stop a speed wobble is to place your knee against the top tube to dampen the shaking. I had this happen going over 55mph and luckily knew what to do from many years ago. It turned out to be a loose headsed on a threadless stem. Good luck

Bob Dopolina 

Such a severe speed wobble at relatively low speeds could indicate that something pretty serious. Have you been in any crashes? Is there a buzzing noise or a creaking noise coming from your fork? This sounds like frame alignment of a damaged steerer tube. Are there any hairline crack visible on your fork or frame?

mustang1

Actually now that you mention it, that's exactly what I done (one the 2nd wobble), putting knee against top tube - it just felt natural.

mustang1

Never been in a crash, never even dropped the bike. Bought it new, 1 year old now. I get creaking from the bike time to time but I *think* that's the seat post. The carbon forks look ok.

Wrt headset, I wont discount it could be this, but every time the bike is just fine, handling is great (it's my first road bike so nothing to compare to), climbing is fine, on flat roads it's great. This is the same route I travel all the time. If it was the headset, wouldn't I notice the problem all the time?

Dave Moulton

I wrote an article about shimmy here.

filtersweep

thank god for an article that does NOT cite harmonic frequency and frame oscillation---

AndrewP

I does in the fifth paragraph

Mr. Underbridge

It does. It just uses different words.

I'm not sure what you are thinking causes such wobble other than some sort of harmonic constructive interference. Wobble fairies, perhaps?

Dave Moulton

Wobble Fairies, I love it. There is a group that doesn’t believe in gravity, but rather that some divine force is pushing us down. Maybe this same divine force just grabs your head tube and shakes the sh*t out of it.

DMF 

Dave! Good article, and I'm really looking forward to exploring the blog. Thanks for the link!



I have a wobble fairy. It wants to be petted, like my cat. Take my hands off the bar and it starts pouting and flopping around until I put my hands back on. (Damn cat!)

Bob Dopolina 

Wobble fairies! Wobble fairies! I've seen them. They're everywhere!

gr8rcake

This looks like a real problem. Some people over here have seen speed wobble issues too.

TalkingHead

would a steel frame bike, like a Jamis be less suspect on this death wobble? it seems some of the Alum frames like the cannondale R5 with the flexy seat stays, and flex forks might be a cause? from the other forum link above. Steel is heavier, but seems better to me, but im a noobb

Bill Kapaun

15 MPH is pretty slow to experience this.
I'd also inspect the spoke tension. Maybe some there flexes enough to get the wobble started.

freako

Very good article in deed. But you state the taller you are the more likely you are to have this problem-how tall is taller? I'm 6' 5'', been riding bikes for more then 50 years, have a small stable of 7 road bikes plus 1 MTB I bought over those years; done a lot of road riding from racing to heavy touring, and rarely had this problem that couldn't be taking care of by simply moving the front tire (sometimes the rear) usually quarter of a turn on the rim. I know my situation can't possibly be due to the trail since I have different trails depending on whether it's a road bike or touring bike. I also have nothing but lugged steel bikes, but I wouldn't think aluminum would have an issue since the big tube AL road bikes are very stiff and thus shouldn't have any frame flex with either long or short trails.

Maybe I'm just lucky...of course so is my best friend who is also over 70 (as I'm am) and we still race today (usually in triathlons where he runs and I ride and another friend swims), but even he's been biking for over 50 years and he's never experienced this either. I do admit I've been talking with some of my other riding buddies due to this post and a few have experienced shimmy but these were two carbon fiber frames, one on a small diameter AL frame (Vitus), and one on a light steel brazed frame and all were racing bikes with short trails. The only person I know that tours besides myself has an AL touring frame and he's had no issues with the longer trail. Any connection with the type of frames?

Your blog is very informative, thank you for sharing it with us.

gr8rcake

Does anyone know of getting rid of a speed wobble by reducing the rake on the fork to increase overall stability? Would that be a good counter measure?

BreakingWind

Check out Calfee article here:

https://www.calfeedesign.com/forksymmetry.htm

Captain Slow

Before you get too deep into frame geometry and all that, examine both wheel hubs. See if there's any side-to-side play in the bearings. If there is, adjust it out. (Just not too tight...)

I had a tankslapper like that on my commuter bike... European Specialized Crossroads, Velocity Glider wheels, Forte ST-K tires. Scared me so bad I screamed like a little girl until I got the thing stopped. It did it again as I descended into my subdivision, contemplated walking it home...

I examined the whole bike... All I could find was some... I wouldn't call it excessive... play in the rear wheel bearings. Once the wheels were off, I saw where one of the rear bearing lock nuts was loose enough to spin off with my fingers. Hmmmm.... Good thing I don't inspect passenger airliners...

I adjusted both wheels, and a year later, no wobbles.


One other thing to have a look at, while the bike is upside down with the wheels off: Check out the carbon fork on that Allez. Really look it over for cracks... You might find some in the paint... They're just cosmetic. Grab both fork legs and 1) pull them apart, 2) push them toward each other. If the fork is okay, you won't be able to break it with just arm power. If it's failing, though, you'll find it.

I'm betting on a loose wheel bearing. Good luck.

DannoXYZ 

yeah something that severe at that low of speed would seem to indicate a bearing-adjustment is too loose. I find that sympathetic-vibration related wobbles don't occur until 45mph+. After 60mph or so they die out because the frequencies are higher.

Randallissimo

I am currently experiencing the very same problem with an 08 Bianchi Brava, steel frame, carbon fork and seat post. It happened the first time at 18 mph on only my second ride on an almost flat incline. I clipped a pebble and the front fork oscillated so bad it scared the crap out of me. I could not make it stop, and braking to a halt was difficult. I brought it in the next day and they lowered the stem (it's adjustable), trued the front wheel a bit and took off the little spoke reflectors. They also instructed me to ride on the down bars when going downhill.

150 miles later, all is well until going downhill at about 20 mph as I transition from the hoods to the downs it happens again. This time in traffic. It started as I had one hand on a hood and one on a down bar. It started in the fork, but then I could feel the frame shake, too. It shook so bad I believed I was going down, I could not control the bike. I did manage to get it stopped without dumping, but now I am scared of that bike. I brought it back to the shop and they took it from me, worried it was going to kill me. They called Bianchi and now are trying to figure out what is going on. In the meantime I have to ride a DBR road loner!

I suspect a defect in the carbon fork, but I really just guessing. Pretty scary stuff, though.

cachehiker

My Felt has always had a touch of wobble, always around 42 mph. It's not terrible but I find myself watching my speed a bit and preparing to either keep the speed down or ride through it to 45 mph.

On one occasion I had the dreaded death wobble. I had crashed hard on a recent charity ride after somebody else lost control and landed on my rear wheel. It was the first big ride after getting the bike "fixed" to the tune of about $250. It was a steep descent on an uneven road surface in Arches NP. Scared the hell out of me. I later found a crack had propagated through the carbon reinforced fork over the last 200 miles or so, most likely from damage sustained in the crash. Other things like a stripped crank bolt and a pedal that snapped in half eventually manifested themselves in the months that followed the crash as well.

OK, anyway, I replaced the 45mm rake fork with a 43mm rake fork and there was much less wobble than there ever was before. However, the fork is supposedly stiffer and lighter and full carbon so there were a lot of factors beyond rake involved.

I guess my conclusion from first hand experience is that a fork with one leg slightly stiffer than the other from poor process control or whatever can cause a wobble too along with dropouts being misaligned. I suppose the same applies to the stays and there are the wheels and their bearings to consider too.

Winnershcyclist

I have had it happen to me yesterday straight hill down smooth road at 22mph scared the hell out of me.

I was on drops too

Couldnt get control and really did think I was going to get dumped.
have cycled this route many times and had done other hills just before no problems

I had it happen last year on a shorter straight

no known issues with the bike

davidad

Shimmy or Speed Wobble by Jobst Brandt

gsa103

Since you've done the route before without issue, that sounds like something mechanical. Were you carrying any extra load (bags or backpack) that might have contributed? 22mph is on the low end to see wobble.