Speed wobble

Muckers · 08-04-2012 07:58PM #1

While on a descent on the Etape Ras Mumhan yesterday travelling at approx 50kph my front wheel began to wobble uncontrollably. It frightened the crap out of me when it happened. On a previous thread on the same subject a couple of years ago I read that if this happens then the rider should grip the top tube between both knees, and keep a firm grip on the bars. I tried this but it got worse, so instead I stopped pedalling and kept control of the bike until it slowed enough for the wobble to stop. I got of the bike and checked the headset and wheels etc but all was fine, but after this happened I lost my nerve on any further descents for the remainder of the event. There was a very strong crosswind at the time coming from the left and I think maybe this was the cause of it. Another rider suggested that it could have been caused by my Ksyrium SL wheels, as they have a slightly deeper section than the average wheel.

Any ideas or advice?

ROK ON · 08-04-2012 08:04PM

Hi.
I had my first ever speed wobble yday on Etape Ras Mumhan. I am also on Kyriums.

Where did it happen. Mine happened on the very first descent, right after the short climb out of Ballyferriter. I think the descent was into Ventry where you took a sharp left at the bottom.

Mycroft H · 08-04-2012 08:08PM

I've had it on a Trek 7.4 fully loaded with panniers in Kerry. Bit scary alright. Lift yourself out of the saddle, just a fraction of an inch. It should help a lot

Its more down to the inherent elasticity of the frame. Its the harmonic vibration of the bicycle and the rider. Get your rigid weight out of the saddle will help fix things. Clenching and gripping only will make it worse.

Jobst Brandt has a better explanation of it.
http://www.sheldonbrown.com/brandt/shimmy.html

Muckers · 08-04-2012 08:17PM

@ROK ON. Same place alright. Coincidence or what.

ROK ON · 08-04-2012 08:20PM

There wa a farmgate with a few people standing there on that descent. I bet the gate let thru a gust of wind, as we were otherwise sheltered by hedge rows.
I feathered the brakes and saw that I was hitting 68kmph. Just gripped toptube with knees and sat up to air brake.
Very scary.

AstraMonti · 08-04-2012 08:23PM

Here is a good read about it as well: http://www.cyclingtips.com.au/2011/03/speed-wobble-when-the-bike-shakes-its-head/

Muckers · 08-04-2012 08:27PM

@BX 19. That's an interesting read. My frame is a Kuota Kharma, and only last week I lifted my saddle by about 10mls, which according to the article, increases the onset of shimmy

ROK ON · 08-04-2012 08:41PM

Now that is a conincidence, as mine is a Kuota also (Kebel).
I am aware that several folks riding Felts have experienced speed wobbles. I have not experienced wobbles previously on fast descents. I am hoping it was a cross wind as opposed to a frame wobble.

alexanderomahon · 09-04-2012 10:53AM

Had this three times now on my planet x and it was always on descents in cross winds.

Don't like descending at the best of times, but now I am really cautious, especially if windy.

Getting a bike fit next week and told this may help.

Konkers · 10-04-2012 02:24PM

Glad to see I'm not the only one. I've had this on two occasions on my lapierre on the same spot (decending on the upper part of the pine forest road coming from glencree and heading to rathfarnham). Scared the living bejaysus out of me both times. First time it was wet and not windy. Second time it was dry and windy. I managed to stop both times but was lucky that the road ahead was straight. When I got off the bike to get my nerve again I checked everything on the bike both times, brake and wheel alignment and could not figure it out and when I looked on boards there was no tread on it. I have a nasty suspicion on this spot it has to do with the road surface i.e. If you assend that way and look at the other side o fthe road a couple of hundred meters before the new tarmacced section you'll fell its wavy (contours on the road surface that cause the refraction to ripple up through the moving parts of the bike, i.e. me and the wheels) probably making me shift weight and grip the bars harder. Two good articles. I'll be changing bikes soon, this just gives me another better reason:D.

Lumen · 10-04-2012 02:28PM

I've only had it once that I can remember, on my titanium Enigma when I was hands-off on a shallow descent.

It calmed down when I held the bars and did the knees-to-toptube thing, and didn't reoccur after I'd tightened the headset.

I don't think wind or wheel cross-section should be a factor. I've never experienced this with 50mm rims in high winds.

seamus · 10-04-2012 02:29PM

I still have no confidence descending from Sally Gap to Manor Kilbride because of the time I got a speed wobble there. Always seems to be a raging crosswind on that section. Which is a pity because otherwise it's a savage descent.

ThisRegard · 10-04-2012 02:31PM

As long as you remember that bloody right/left at the bridge.

kenmc · 10-04-2012 05:13PM

I don't think I've ever experienced a speed wobble, and I *love* to descend as fast as I can (was disappointed on saturday it was windy and was only able to get 70.4km/h coming down from Seskin despite pedalling as hard as I could!)

moggs1972 · 10-04-2012 05:57PM

I've experienced speed wobble 3 times on my canyon, oddly enough only with the ksyrium SL's but each time wind seemed to be a factor, twice on the N7 when large truck passed by at speed causing gust of wind and once with a strong crosswind when the front wheel hit a stone. scary stuff, each time i eased the grip on the bars, lifted my ass off the saddle a bit and the wobble stopped.

dermur · 10-04-2012 07:15PM

Speed wobbles frighten the gick out of me. Perversely, the tighter you grip the handle bars the worse they'll feel. So, against all your better judgement ease off on your grip to get some instant relief.

Pressing knees against the top tube is also good at combating speed wobble and generally unloading weight off the saddle (sit back).

But these tactics are all aimed at relieving the symptoms and aren't a cure. Changing wheels usually offers an instant cure although that's not to say that the frame itself isn't the root cause in any particular case.

Here's a good explanation too...
http://www.bike123.com/tech%20info/shimmy.htm

Muckers · 10-04-2012 10:58PM

Thanks for all your replies lads. If it happens again, then i'll know how to stop it.

Murph100 · 11-04-2012 07:09AM

Had it about three years ago with a Viner I had back then, almost on any really steep descent I would get a speed wobble, changed wheels to see if that would cure it but no joy, tried everything thing else that was suggested, still no joy. I finally solved it by replacing the stock fork with a Look fork ( big upgrade ! ), instant cure and much better handling as well.

Bottom line, its a combination of You and your current frame, another guy might not get speed wobble with your frame at all, so the only real solution is to ultimately change the frame or the fork.

I've had 3 other frames since I sold that Viner, 2 with the exact same components, and have had absolutely zero speed wobble on any of them.

Iwernia · 11-06-2013 08:24PM

New Ksyrium SL's fitted and had my first wobble coming down Glengesh recently in the high 70's but was comfortable enough and did not panic but had my 2nd & 3rd wobble coming off the Wicklow Gap on Sunday in the 60's that scared the bjaysus out of me. I thought the crosswind was a factor and got the bike slowed but when the speed climbed again the front of the bike was out of control, I had a motorbike behind blowing at me but little did he know I was only a passenger. I had a loose grip on the bars and just let the bike go until it settled, I didn't get over 45 or the rest of the day. I am blaming the wheels as i never experienced this with Dt swiss wheels that the Mavics replaced.

brasshead · 11-06-2013 08:53PM

Iwernia wrote: »

New Ksyrium SL's fitted and had my first wobble coming down Glengesh recently in the high 70's but was comfortable enough and did not panic but had my 2nd & 3rd wobble coming off the Wicklow Gap on Sunday in the 60's that scared the bjaysus out of me. I thought the crosswind was a factor and got the bike slowed but when the speed climbed again the front of the bike was out of control, I had a motorbike behind blowing at me but little did he know I was only a passenger. I had a loose grip on the bars and just let the bike go until it settled, I didn't get over 45 or the rest of the day. I am blaming the wheels as i never experienced this with Dt swiss wheels that the Mavics replaced.

I too experienced my first speed wobble on Sunday in the final 40km coming down a sharp hill. Think it was caused by me leaning forward and sitting temporarily on the top tube as when I shifted my weight back it stopped. Thanfully all the other descents passed off without incident.

ednwireland · 11-06-2013 08:53PM

sl's front wheel definitely catches the wind (flat spokes i assume) but you get used it

iwernia i'll take yours off your hands if you want

Konkers · 12-06-2013 10:47AM

Konkers wrote: »

Glad to see I'm not the only one. I've had this on two occasions on my lapierre on the same spot (decending on the upper part of the pine forest road coming from glencree and heading to rathfarnham). Scared the living bejaysus out of me both times. First time it was wet and not windy. Second time it was dry and windy. I managed to stop both times but was lucky that the road ahead was straight. When I got off the bike to get my nerve again I checked everything on the bike both times, brake and wheel alignment and could not figure it out and when I looked on boards there was no tread on it. I have a nasty suspicion on this spot it has to do with the road surface i.e. If you assend that way and look at the other side o fthe road a couple of hundred meters before the new tarmacced section you'll fell its wavy (contours on the road surface that cause the refraction to ripple up through the moving parts of the bike, i.e. me and the wheels) probably making me shift weight and grip the bars harder. Two good articles. I'll be changing bikes soon, this just gives me another better reason:D.

Jaysus, what was I on :rolleyes:, "wavy road" ?????????.

I did change wheels on the old bike and tightened the headset. It may have helped to alleviate some of the problem. However, I never really had confidence in that frame again. I suspect I just slowed down a lot. My decending speed was never more than 50kmph after those wobbles.

I agree with one of the posters here who say its the frame. My new frame is carbon and very slightly bigger. I have lots on confidence decending and use the brakes a lot less. Recently I hit 68kmph and did not notice. I would not have done this on the old bike.

funkyjebus · 12-06-2013 11:21AM

seamus wrote: »

I still have no confidence descending from Sally Gap to Manor Kilbride because of the time I got a speed wobble there. Always seems to be a raging crosswind on that section. Which is a pity because otherwise it's a savage descent.

Got it there a few weeks ago myself when there was a crosswind and I had just put on my new 30mm wheels. Scared the crap out of me, now I'm afraid to go back down again.

Agreed otherwise a great descent, especially if you get a tail wind.

Slo_Rida · 12-06-2013 11:27AM

Surely it's the wind causing the rider to wobble/shake as opposed to the wind actually wobbling or shaking the bike?

The Noble Nudge · 12-06-2013 12:19PM

Ive had two wobbles on the same frame different wheels.
Ballinascorney hill (70kmish not sure of the brand) and Montpelier hill (50kmish on mavic askiums less then a year old) put it down to wind but got some fright....hasnt stopped me on downhills though.

sconhome · 12-06-2013 12:29PM

dermur wrote: »

Pressing knees against the top tube is also good at combating speed wobble and generally unloading weight off the saddle (sit back).

and helps keep your bum closed when the descent gets really hairy. :eek:

Iwernia · 12-06-2013 05:19PM

Slo_Rida wrote: »

Surely it's the wind causing the rider to wobble/shake as opposed to the wind actually wobbling or shaking the bike?

Christ no, I can assure ya the rider was not wobbling, the front of the bike was out of control, bouncing. I have read up on a few tips online and will put them in to practice the next time or not.

Buzwaldo · 15-04-2014 11:08PM

Thought it better to resurrect this thread than start anew, as many aspects covered here already.
Anyway I have had a few speed wobbles in the last year, turning me into a nervous descender, but the Tour of Wicklow last weekend convinced me that I need to address this issue.
I had 2 wobbles there and almost got into a third. Due to this issue I seldom break 40kph while descending now, and this take the enjoyment out of such an event. Very hard work to keep with a group, and almost prefer going up than down.
If/when it happens again I will try some of the fixes mentioned on various fora such as shifting weight forward, and onto pedals rather than saddle, but I don't believe I would be able to grip the top tube with my knees (as a late and recent convert to road biking my handling skills are very moderate).
Appears from reading up that wobbles are caused by harmonic oscillation of the bike/rider unit which hits a particular resonant frequency??
My question for the knowledgeable folk of 410 is, which of the following might be of some help in reducing the chances of going into a speed wobble?

change of wheelset
change of tyre width or inflation pressure
change of stem length

I know the obvious answer is new bike, and believe me this is being considered, but I'm quite fond of my current rig and would hate to change if I could solve this more easily and regain some of my (modest) descending mojo.

Raam · 15-04-2014 11:11PM

Buzwaldo wrote: »

Thought it better to resurrect this thread than start anew, as many aspects covered here already.
Anyway I have had a few speed wobbles in the last year, turning me into a nervous descender, but the Tour of Wicklow last weekend convinced me that I need to address this issue.
I had 2 wobbles there and almost got into a third. Due to this issue I seldom break 40kph while descending now, and this take the enjoyment out of such an event. Very hard work to keep with a group, and almost prefer going up than down.
If/when it happens again I will try some of the fixes mentioned on various fora such as shifting weight forward, and onto pedals rather than saddle, but I don't believe I would be able to grip the top tube with my knees (as a late and recent convert to road biking my handling skills are very moderate).
Appears from reading up that wobbles are caused by harmonic oscillation of the bike/rider unit which hits a particular resonant frequency??
My question for the knowledgeable folk of 410 is, which of the following might be of some help in reducing the chances of going into a speed wobble?
change of wheelset

change of tyre width or inflation pressure

change of stem length

I know the obvious answer is new bike, and believe me this is being considered, but I'm quite fond of my current rig and would hate to change if I could solve this more easily and regain some of my (modest) descending mojo.

Knees on the top tube are probably the simplest way of sorting this out and it is such an easy thing to do. When you achieve it, and you will achieve it, you will realise just how easy it is to do.

Practice this for me, pedal along an ever so slight decline, fast, then when you have a good head of steam built up, start to freewheel. Pinch the top tube with your knees, or even just lean one knee against it. That will achieve the same effect: breaking the oscillation. You won't get the speed wobble in that practice session, but keep practising it and it will become a reactive thing which you automatically do rather than something which you have to think about.

Konkers · 16-04-2014 07:36AM

Before u change any parts check your wheels are fully pushed into the lugs of the front fork and rear stay.
I'd also get a professional mechanic to look that your headset is tight and fit for use.

Since I posted above I've been using the bike that used to wobble all winter and have had no wobble incidents. The only changes I've made are new wheels. The old wheels were fulcrum racing 7's. New ones are much heavier ( hope hubs on open pro rims and 36 sapim spokes). I used to think it was the bike so could not bring myself to sell it. Now I have a great winter bike........

couerdelion · 16-04-2014 09:40AM

Had a speed wobble last week at nearly 80kmh. I'd done a lot of descending that week but that was the fastest I'd hit and had to ease back. It was either the wind on the deep rims or the wheel might not quite have been seated right. Either way it was disconcerting - didn't slow me down afterwards though

Speed wobble

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