A nice sunny day in the mountains so I thought that I'd take a ride on my new bike down Victoria Pass.

All went well until I hit about 60 km/h and the bike suddenly began to violently shudder. A rhythmic shaking possibly in time with wheel rotation and as if I had a really badly unbalanced wheel. It really felt like I was about to be dumped off onto the road, but managed to pull over and stop with the wobbling continuing down to quite a slow speed. There was nothing I could find wrong with the bike and it rode nicely, afterwards, but not as fast :-)

I've done Vic Pass before on my other bike with narrow light wheels instead of big heavy mountain bike tyres going faster with no problems.

So, any suggestions as to how I can stop this happening or what's causing it? Is it just an unfortunate characteristic of the frame itself? Gotta say I'm a bit reluctant to test it again although at least this time the only vehicle behind me was ironically, an ambulance.

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Thanks for the ideas.

Yep, that was 'me' in the video. It felt like some sort of resonance. The sensation was if the wheels had suddenly gone egg-shaped & also yes, I may have just lightly tapped the brakes to get it started. I suppose that's one solution: never touch your brakes while descending steep hills.

Tyres well seated, no reflectors but first time down there on this bike.The scary thing is that there was no build up. I think next time I'll be descending with both knees firmly pushing against the top tube.

If it's never happened to you before, you need to think about what's changed on the bike. Is it the speed? Weight distribution? Looser (or tighter) headset?
I've never had it as violently atin that video. That would be spooky!

Many years ago I once owned a Kawasaki Z1000. At one period during my ownership I could not push the bike past a certain speed (embarrassed to admit what that was) without the bike getting the death wobbles. I survived to finally identify that the rear tire was ever so slightly screwed on the rim. Check that your tires are running true.

Death wobbles at high speed on a motorcycle would be scary!   

All people are correct. You need to change the dynamic mechanics of the bike. Basically move the weight, or change it's stiffness. Sometimes I loosen the grip and sit back, other times I brace, lean forward, and power even harder.

My cargo bike had it really badly at about 20km/hr. It is too big for me to make much difference to, but I solved it by over tightening the headset.

So you'd recommend a Software Engineering approach? Try descending that hill again and try to reproduce the problem?

https://stackoverflow.com/a/234152/2905720

Hang on, are you sure you are in IT Timothy?

Because if so, you should know the solution is always "upgrade"

PS: hint: it works for bikes too

I thought the solution was turn it off, wait 2 minutes and then turn it back on.  

The really unnerving thing about speed wobbles is that gripping the bars (more) firmly seems to just make it worse. It is counter intuitive. Both knees on the top tube , braking but pushing on the pedals still, as light a bar grip as possible, and a straight line (regardless) are all what I do. Take some poo paper with you as that can be needed.

Interesting read,

key words seem to be - a bit frightening and poo paper.

I am yet to experience this shake, but I have had lesser trouble with rough surfaces on a fast decent. Rear  wheel wanted to lift or was it my imagination. We you suggest shifting my weight back?

I got the death wobbles two days ago descending fast on gravel.  I probably hit a washboard bump at a frequency that set it off.  Heavy on the pedals, light on the bars and knees on the top tube steadied it up - what Noel said.  Usually you can feel a wobble building up and early intervention can settle things before the wobble gets out of control.  

Agree. Normally it can be shut down. But it can get so hectic that you feel for sure you are going to be tossed off. I had one where I ended up having to go straight in order to stay on and that meant, in that case, the bush as there was a corner in front and bush straight ahead. On the Bridle Track near Sheffield Tas. It could have been a road cutting or barrier so I was lucky. It may be more likely to develop when coasting. I've noticed that braking whilst pushing on the pedals does trim it back. More forces being applied in more spots I guess.

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