are you a skilled rider or a nervous rider?

wobble can be cause by a lot of factor including the bike or rider itself
-stress, gripping handlbebar too hard
-frame bend/out of alignement
-wheels
-headset issue

etc

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Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
Instargram

This has happened to me too (funny - also with Bianchi from that era). At the time I had 35 mm setback seatpost and realitevely short 90 mm stem, i.e.my position wath quite backwards. After I moved my position forward, using 25 mm setback seatpost and longer 110 mm stem I’ve never experienced speed wobbles on this bike anymore.

Possible causes are combination of bike construction mistakes, rider position and who knows what else.

Can be a range of factors. Maybe with your set up it's exacerbated by stiff deep wheels and an older frame that has developed more flex. Weight off the saddle slightly, lightly grip top tube with knees, loosen grip. Consider changing handlebar set up to get more weight on the front, especially with the deeper front wheel.

There are lots of potential causes as mentioned by the previous posters.

-Check for a loose headset.

-Check for out of balance wheels (place the bike on a workstand and spin the wheels up to speed to see if the bike stares to shake). I had high speed wobbles caused by an out of balance H3 back in the day. You can fix the balance with molding clay or 2-part epoxy.

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ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

No idea the cause, but a common remedy is to pinch the top tube with your knees or thighs.

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Dimond Bikes Superfan

I've had it twice before, doing about 50mph down the same hill, the back wheel was going crazy, felt like it was buckled. I couldn't see any issue with the bike, wheels, tyres. And gripping the frame with my legs/knees did nothing. This was a Boardman road bike, which I think was a Chinese built open mould. My next bike was a BMC SLR01, significantly better and it went down the same hill at a higher speed with no issues.

I personally think it's the frame, perhaps a cheap or poorly constructed frame is going to vibrate more?

30mph seems a fairly low speed to be getting speed wobbles though.

Thanks all, for the feedback. To answer a few questions, I'm a reasonably skilled rider, having road raced motorcycles on closed circuits and mountain bikes for several years. I've never pinched my knees together (but might give it a shot) and tend to stay loose and balanced when descending. I'll go through the bike and attempt to sort as many of the possibilities as I can based on your recommendations (i.e. wheels, bolt tightness, etc) Worse case scenario I can petition my finance department (read: wife) for an upgrade. :) Thanks again!

Were any trucks or other vehicles passing you as you were going downhill?

I had an old Boardman air something which was very light, rigid, and with a very short stem (because the frame was a bit too long for me), that would often give me speed wobbles at around 70km/h or so.
I since moved on to a cube litening and never had this happen again.

I think equipment had a big impact. No matter how I gripped, relaxed, moved my knees or what not.
I somewhat suspect the short stem was the issue, because I moved it once to my cx bike, and could sort of start triggering wobbles by riding slowly without grip from the hands, hitting on the side of the handlebars and seeing how it relaxes to straight with or without oscillations. The original longer stem there was much more stable. Maybe a light bike with rigid wheels emphasizes this tendency? I don't know, since I changed the road bike for other reasons around that time so never figured it out fully.

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https://besse.info/
https://www.strava.com/athletes/2012033

Until recently, I never experienced this issue. It has happened several times. It is always triggered by a truck passing at high speed. A very unnerving experience.

check your bike:
- wheels
- headset
- handlebar

check that the frame is ok

check the freehub

You don't have to be a bad rider to get speed wobbles, but it's good to cross that off the list.

A speed wobble fundamentally comes from a resonance in the bike/rider unit, a vibration that 'echos' through the frame/rider back onto itself at the very peak of the next vibration, building itself like a kid on a swing into larger amplitutdes. This is why the knees on the top tube are so effective, you're dampening the vibration before it has a chance to return to the source and grow.

It's common for wobbles to happen when at a very steady high speed for an extended run. Happening indiscriminately above 30mph points to a pretty major vibration or alignment issue in the bike.

All of the advice of where to look here is good, I'd also add that tubular tyres glued not perfectly straight can also throw some big wobbles.

I am a very experienced rider, I worked in the bike industry for 10 years, and I have owned probably 15 different road bikes in the past. I had one bike that had a horrible speed wobble that kicked in at around 42mph. Its a total rabbit hole to try to chase down, you will hear lots of suggestions as to what to do. After literally trying about 5 different things, (stem length, different wheels, seat fore aft, relaxing more, etc.) and testing those things by going up to a nearby mountain that has a 50+ mph downhill, I sold the bike.

Its not worth it when you have had over a dozen other bikes that were totally confident descenders, were set up the same way, and never exhibited the crazy wobble.

Do you have a different set of wheels to try? If so, I'd give that a shot first to see if you can rule out your wheels as the problem.

I had a bike with speed wobbles before, and it was due to a notch in the headset. Replacing the headset bearings fixed it.

A friend of mine bought some bontrager wheels and started getting wobbles. Switched to zipp and he was fine. I'm not saying all bontrager wheels are bad, or all zipp wheels are good. Just saying it could be wheels. It could be headset. It could be tires. It could be lots of things. If the bike wobbles with different wheels and tires, then you could conclude that your wheels and tires probably aren't the issue

i would definitly look into finance departement options..... once a bike had a wobble...the bike is curse and need to be replace with something better, newer, shinier. it s a matter of safety..... GET A NEW BIKE

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Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
Instargram

'death rattles' can happen in lots of different sports, when going fast. Ice speedskates, inline speedskates, ice hockey skates, downhill skiing even some sailboats (but that's different).

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Kevin

I tend to agree, although I didn't know you could get wobbles skating. I do recall getting "tank slappers" racing motorcycles. Steering dampers were a wonderful invention. Much better than cleaning the backside of your leathers. :) That being said, I also realized that after I tighten and check stuff I need to ride downhill at high speed again to see if it solved the problem.

The downside to this short-term solution is that being in that position increases the chances of shitting your pants, which is quite likely when you get the death wobble on a descent.

It's hard to squeeze the top tube and your sphincter at the same time.

My wife's bike had the same problem, and it kicked in at anything over 26 mph! Tried changing all the usual suspects--stem, headset, wheels; none of them solved the problem. Bike shop finally found that the rear dropouts were just a teeny bit out of alignment, and this would cause the wobble once the critical speed was hit. They did something to get the rear dropouts in perfect alignment, and the wobble disappeared.

On a different note, I had the same problem on one bike at exactly 42 mph when descending on some Zipp wheels. I changed the wheels and the fork and one (or both) of those changes fixed the problem.

Good luck finding a solution.

Mine was a loose headset. When I relocated the spacers and apparently I loosely installed the fork + headset + stem.

A youtuber was comparing cheap open mould Chinese frames with more expensive frames from big companies and was saying whilst the weight, strength, geometry might be OK (often they're not) there are many other aspects to building a quality frame and went on to demonstrate the difference in stiffness, The rear stays on his BMC frame were very stiff, on the Chinese frame (Winspace I think) were really flexible. You could imagine there would be little difference between them < 30mph, but over 35/40mph the differences could be significant.

So perhaps all those youtubers promoting Chinese frames, perhaps they need to ride them fast and hard and then see what's what.

What makes me worried about your situation is that the system (you, your position, frame, wheels, etc) was apparently unchanged yet the speed wobble surfaced.

I think something changed that you haven´t noticed yet. I agree with checking wheels, headset, etc, very closely.

I have had systems (me, bike, wheels, etc) that could descend insanely fast and steady. And a 2-3 systems (new wheels, new position) over the past 35 years that produced absolutely unbelievable terrifying speed wobbles at relatively pedestrian speeds.

There are been prior smart posts on this subject. The physics, if I remember correctly, are fascinating. And deep.

Good luck.

As stated before, it's resonance. Pedaling or touching the top tube with your leg(s) will solve it everytime or prevent it from happening.