Speed Wobble - thoughts \ advice appreciated

Derbyrich

Before I purchased my new bike, I had experienced speed wobble once.

With my new bike, it has happened three times in the relatively short space of time that I have had it. I have researched the topic before and understand the causes and the steps to take to stop it once it starts. However, what I find interesting with the times it has happened on the new bike is that all three have been when I have been seated and pedalling, not free-wheeling. It is therefore hard to put in to practice the advice on prevention by putting my knee against the top tube. My experience with this bike also seems to go against the norm for when speed wobble occurs.

Any thoughts \ advice?

sean19690

I have also experienced this problem, and like yourself has researched. I was amazed to find out how many sports with high speed experience this problem. I was having this problem in the same place heading towards speeds of 39mph. I checked the stem, ,etc. it did reduce when i relaxed more but ultimatley i had to slow down.

My conclusion was that, me, bike, speed and environment creates a particular frequancy, that leads to wobble.what i find strange is others i ride with do not experience the same wobble.

I don't no how significant the seating and peddling issue you raise are. I think it still comes down to technique, relax and push through

Derbyrich

Interesting. I have focussed on being as relaxed with my grip on the bars and this seems to have a positive effect, but not a total removal of the problem.

The point about some people suffering and others not is interesting. Bike type I believe is a factor there. I am riding the same roads,in the same way, on my new bike as I have on my Winter bike, but having far more issues.

I also wonder whether my pedalling technique is a factor. I am not aware that my pedalling technique is bad, but maybe it is a contributing factor when I ride a significantly lighter bike than I am used to.

One of my friends has also done some reasearch in to this and he believes there is quite a lot of evidence of people having issues when moving to a lighter bike that resolves itself over time as they become more in tune with the bike. Is that similar to your situation Sean?

walleyes

Wierd this speed wobble thing. In 29 years of racing and riding I have never experienced it [don't want to either]. Any opinions out there as to why it seems more common now or is it just you hear a lot more now we have the internet?

fossyant

A lot of it is down to geometry as well - if it's happening often, then it will be that.

My best bike has never done it, at speeds of up to 60 mph, my training bike has done it once slightly, and was brought under control by braking on the rear - due to strong cross wind.

I had a bike that would speed wobble quite badly - but only when mudguards were fitted.... you'll have to try and find the cause.

Derbyrich

Thanks Fossyant.

I did some more digging on the internet last night after posting and found a few references to trying shorter stems to get a little weight off the handlebars. I will consider that as an option.

Obviously I can't change the geometry of the frame itself.

cougie

I read it was more frequent with compact frames ? That does kinda fit with my experience anyway.

Al_38

Can't say i have experienced this, but could it be something to do with the combination of wheels and forks.
I'm an engineering student and one of the things we have covered in fluid dynamics is vortex shedding. basically if you have a body moving fast relative to another body (i.e. spokes and inside of fork legs) then the vortex shedding will stop being nice and predictable and instead become non-linear, leading to instability. This is likely to only be caused at a certain frequency - so depending on how fast you go and how many spokes you have on the front wheel.

So, could you try a different front wheel? And are the forks roughly of the same profile as your old ones?

Al

bigal.

Just curious. What make of bike is it.????

El Gordo

In about twenty years of riding I'd never experienced a wobble either until this happened a few weeks ago...

http://www.bikeradar.com/forums/viewtop ... highlight=

I've previously ridden three other bikes up to 50mph+ sort of speeds (two road bikes and a tandem) and never had a problem. The new bike is ligther and stiffer than anything I've had before so I could well believe that the problem is more frequent these days.

My understanding is that is to do with the lateral flex in the frame reacting at frequency in tune with the centrifugal forces in the wheels. Not that that helps mind you. My problem now is knowing what to change then figuring out a way to test it without giving my bike another chance to throw me into the bushes.

Derbyrich

Thanks all.

Al: I think trying the bike with a different set of wheels is the next step. I have SRAM on the new bike and my other road bike wheels are Shimano, so gotta check whether there are any compatability issues there. I believe not as my Shimano cassette removal tool works on SRAM cassettes. The forks are bladed carbon, same as on my Ribble Winter bike, but lighter and more profiled

Bigal: Litespeed. It's a Pavia, their foray in to carbon monoques, with SRAM Force and FSA carbon wheels, stem, bars and seatpost. Gorgeus!

Gordo: my new bike is also lighter and stiffer than my previous bikes. Interestingly, this does seem to go against the opinion of some people that speed wobble is caused \ exacerbated by frame flex.

I think my first step will be to swap the wheels out and I may (based on some comments I have read about weight distribution) try a shorter stem

Steelride

Derbyrich,

I have a Litespeed Pavia. I've never had a problem but then again I dont exceed 35mph very often. I weigh 15st, what about you? Personally I think speed wobbles are more likely with light frames and wheels coupled with a rider who isn't familiar with riding such. Aggressive frame geometry and steep fork rakes won't help either.

Steelride.

balthazar

Thorough explanation of shimmy here:


http://www.sheldonbrown.com/brandt/shimmy.html

Derbyrich

Thanks Balthazar - I read that some time back. It explains well.

Steelride - good to hear that you haven't had the issue on your Pavia. I never assumed it was just the frame that was problematic, but still nice to hear from another owner. Your comments certainly apply to me. I have moved from a 21lbs Ribble Winter bike to a 15lbs Pavia. I am also riding carbon wheels and tubs for the first time. So a lot of change. One of my friends believes I just nee time to get used to the bike. I weigh 12 stone.

A little bit off topic, but how is your frame built up out of interest?

Steelride

Derbyrich,

Mines quite light too, Campag Chorus, Campag Shamal Ultra clinchers and Ritchey carbon bits. I find the frame very stiff and responsive. Only down side is the tall head tube, together with a Cane Creek tall headset I cannot get my bars low enough. The easy answer is to change the headset which I plan to do this winter.

Have you noticed the same with your head tube? My frame is Size L and I'm 6'1".

Steelride.

Ivor Sorarse

I have just posted regarding speed wobble in the Beginners Forum. In my example I have just purchased a lightweight carbon Specialized Roubaix Elite. In many years of leisure cycling with a Trek Hybrid I never experienced this phenomenon yet on my 4th ride out on the compact I experienced this very scary problem.

I noted that the tarmac was not particularly smooth, I was a bit tense as this was early experience on narrow tyres. I was travelling about 30mph downhill and the more I applied brakes the worse the oscillation became. I am about 15 and a half stone and 6ft 4"

Very Scary

dag_on_a_bike

Happened to me last Sunday - Specialized Roubaix Expert, 14.5st, 6'

http://www.bikeradar.com/road/forums/viewtopic.php?t=12591241

ride_whenever

It is very odd how some people experience it and others dont...

I regularly go 35 mph (roughly half of my morning commutes) down a very shoddy road surface and i've never experienced it, kinda curious now...

heavymental

ride_whenever wrote:

It is very odd how some people experience it and others dont...

I regularly go 35 mph (roughly half of my morning commutes) down a very shoddy road surface and i've never experienced it, kinda curious now...

Shoddy road surface is your friend in this case as it means the resonance is disturbed and a wobble doesn't develop. Its ultra smooth tarmac where the problem is most likely to occur. After it happened to me i now dread long smooth straight descents where there's not much chance to break up any oscillations developing. Pedalling, shifting weight, breaking, cornering and rough road surface all mean no resonant forces develop. Hence I now prefer descents that tend to have plenty of chances for hard pedalling and breaking for tight corners. Alpe Du Huez for example is a nicer descent for me than the Glandon which has long straight sections.

Also, I find wind a problem. I think this is because you tend to tense up when a gust blows you sideways. This tension in the body means a wobble is more likely to develop as the body acts like a damping system usually. If you're tense, that system is less effective.

Its worth knowing what you should do in the event of a wobble just incase you ever do experience one. Relax, grip the top tube with your legs and lessen your grip on the bars seems to work.

The above might all be mumbo jumbo but its what I gathered from reading the many threads on the subject. I also changed my fork to a carbon number which seemed to help.

fenski

I've experienced speed wobble a couple of times on my Roubaix Elite.

From my experience the common factors were: a cross wind, it/I was cold, I had perhaps inflated my tyres to a higher pressure than I normally would.

I'm not saying it's definitely a solution - but for those looking to experiment - I'd suggest running your tyres at a slightly lower pressure for a while and seeing if that improves things.

Bart Puss

I have a Pinarello Paris and have experianced speed wobble once...this was on last years Etape Du Dales as I started to hurtle down Fleet Moss to Hawes.

The ambulance parked half way down for a few short scary seconds looked like it might be in for some business, but I clamped my knees to the top tube which stopped the wobble, slowed down and got down ok.

Not sure what caused it as I had been down the same descent on the same bike with no problems a while previously... from memory I went down that time resting on the tops...the speed wobble occasion I was down on the drops.... so maybe the weight distribution was a little differant.

That spooked me a bit for some of the other descents until I got my confidence back on the descent to Nateby which I did on the tops and flew down. :?

Fleet Moss descent is straight whilst the one to Nateby was suitably twisty...thinking back the Paris with some stiff carbon bars does get a bit twitchy at times and I think there was a bit of a cross wind but whilst down on the drops it seemed to magnify the wobble for some reason...not exactly sure why... the road surface seemed a bit corrugated as well and it just started to wobble faster and faster till I took corrective steps. Has n't happened since but it does lurk in the psyche at times.