Speed Wobble

[Foxpox]

Need some advice please. I've had a carbon racing bike for a year now and had absolutely no problems on it. If anything I've been a lot quicker and confident down hills. Recently I was heading towards the cradle and had a hectic speed wobble for about 100m going down Cedar Road (65-70 kph) I struggled to bring the bike to a halt and I thought I was going to be thrown over the top. Same thing started happening at about 40kph this weekend, my mates behind me said they could see the front wheel starting to wobble! Bloody terrifying. I read the stuff on the net to relax shoulder,arms and loosen grip on handlebars and also keep weight on saddle but it didn't help. I've checked bike and wheels and everything seems okay. Am I just being a naf, or am I doing something I shouldnt be doing or could there be an issue with bike or wheels. I'm 6ft3, bike was fitted by shop I got it from and a mate who owns his own shop so size should be the problem.

Any advice will be appreaciated

[Spirog]

Check that your tire pressures are correct. Too low and the tire is trying to get off the rim. Too high and some of the ruts on that section will get your wheel bouncing all over the place

[Paulst12]

Have you recently changed anything on the bike? I put a set of wheels on my bike and the alignment was marginally out which is what created the speed wobble. Also may be caused by carbon fatigue ie, if one of the stress arms is stightly weaker.... hard to see with a naked eye but if you apply weight to the bike, it shifts.

[Vetseun]

Maybe tyres. I changed the rubber on my bike and it suddenly developed a speed wobble.

 

Anyway ask Wyatt Earp. I have absolute faith in his wheel building skills and knowledge.

[Foxpox]

Cheers, will try a new set of tyres and make sure pressure is 100%, see if that helps.

Feel like this a bit like playing Russian roulette to see if your gun works

[Shebeen]

this has come up before, can be many things - 

 

https://www.bikehub.co.za/index.php?app=core&module=search&do=search&fromMainBar=1

[Madlight]

Possibly nothing more than your speed, the road surface and your position on the bike hitting that sweet spot. Shifting position and/or changing speed normally helps. Tensing up makes it worse. But for the technical guys out there:

 

it’s a nonlinear bifurcation phenomenon called “Hopf Bifurcation.”
Read more at http://velonews.competitor.com/2013/11/bikes-and-tech/technical-faq/technical-faq-bifurcation-and-high-speed-shimmy_309601#F30qfp61wLSFUvKf.99

[Cois]

Hit a wobble down Kanskop once.  Left a brown stain in my cycling shorts.

 

And that was on 60km/h.  Since then the bike has seen speeds of 70 km/h + (think 94.7 I hit 84.6 km/h, but I do not have that polar data anymore) and did not hit a wobble again.

 

Few things that I did change.  My weight, my wheelset and the tyres. But few things can cause this.  Tensing up and stressing about a mountain pass with a road bike and a few trucks and baboons waiting on the way down...